This PDF file contains the front matter associated with SPIE Proceedings Volume 13102, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The Next-generation Extended Wavelength-MUltiband Sub/millimeter Inductance Camera (NEW-MUSIC) on the Leighton Chajnantor Telescope (LCT) will be a first-of-its-kind, six-band, transmillimeter-wave (“trans-mm”) polarimeter covering 2.4 octaves of spectral bandwidth to open a new window on the trans-mm time-domain frontier, in particular new frontiers in energy, density, time, and magnetic field. NEW-MUSIC’s broad spectral coverage will also enable the use of the Sunyaev-Zeldovich effects to study accretion, feedback, and dust content in the hot gaseous haloes of galaxies and galaxy clusters. Six-band spectral energy distributions, with polarization information, will yield new insights into stellar and planetary nurseries. NEW-MUSIC will employ hierarchical, phased arrays of polarization-sensitive superconducting slot-dipole antennas, coupled to photolithographic bandpass filters, to nearly optimally populate LCT’s 14′ field-of-view with six spectral bands over 80–420 GHz (1:5.25 spectral dynamic range; 2.4 octaves). Light will be routed to Al or AlMn microstripline-coupled, parallel-plate capacitor, lumped-element kinetic inductance detectors (MS-PPC-LEKIDs), an entirely new KID architecture that substantially enhances design flexibility while providing background-limited performance. Innovative, wide-bandwidth, etched silicon structures will be used to antireflection-treat the back-illuminated focal plane. NEW-MUSIC will cost-effectively reuse much of the MUSIC instrument, initially deploying a quarter-scale focal plane capable of the bulk of NEW-MUSIC science followed later by a full-FoV focal plane needed for NEW-MUSIC wide-area survey science.

Prime-Cam is a first-generation instrument designed for the Fred Young Submillimeter Telescope (FYST) in the Cerro Chajnantor Atacama Telescope (CCAT) Facility. Among the instrument modules being developed for the Prime-Cam receiver, the highest frequency 850 GHz module presents unique challenges in optical design, coupling, detection, and readout. The 850 GHz module will incorporate approximately 45,000 polarization-sensitive, lumped-element microwave kinetic inductance detectors (KIDs), which will represent the most KIDs on sky in a single instrument to date. We present the critical aspects of the detector design and discuss solutions to the challenges of efficient optical coupling and a multioctave readout band. Specifically, the designs will include a feature which reduces the inductance across a portion of the detectors by shorting pairs of inductor lines to allow the KIDs to be tuned across four distinct bands across the readout range, all with minimal impact to the responsivity of the detector. Thus, the resonators will be coarsely tuned via the inductance shorts, and finely tuned by etching away small portions of the interdigital capacitors. We further present a comparison between simulations and preliminary results of thermal responsivity. The results of this work will directly inform the design of microwave KIDs for the multi-octave readout architecture as part of the development of densely packed arrays for the Prime-Cam instrument.

SPIDER is a balloon-borne instrument designed to map the cosmic microwave background at degree-angular scales in the presence of Galactic foregrounds. Spider has mapped a large sky area in the Southern Hemisphere using more than 2000 transition-edge sensors (TESs) during two NASA Long Duration Balloon flights above the Antarctic continent. During its first flight in January 2015, Spider observed in the 95 GHz and 150 GHz frequency bands, setting constraints on the B-mode signature of primordial gravitational waves. Its second flight in the 2022-23 season added new receivers at 280 GHz, each using an array of TESs coupled to the sky through feedhorns formed from stacks of silicon wafers. These receivers are optimized to produce deep maps of polarized Galactic dust emission over a large sky area, providing a unique data set with lasting value to the field. In this work, we describe the instrument’s performance during SPIDER’s second flight.

GroundBIRD is a ground-based cosmic microwave background (CMB) experiment for observing the polarization pattern imprinted on large angular scales (ℓ > 6 ) from the Teide Observatory in Tenerife, Spain. Our primary scientific objective is a precise measurement of the optical depth τ (σ(τ ) ∼ 0.01) to the reionization epoch of the Universe to cross-check systematic effects in the measurements made by previous experiments. GroundBIRD observes a wide sky area in the Northern Hemisphere (∼ 40% of the full sky) while continuously rotating the telescope at a high speed of up to 20 rotations per minute (rpm) to overcome the fluctuations of atmospheric radiation. We have adopted the NbTiN/Al hybrid microwave kinetic inductance detectors (MKIDs) as focal plane detectors. We observe two frequency bands centered at 145 GHz and 220 GHz. The 145 GHz band picks up the peak frequency of the CMB spectrum. The 220 GHz band helps accurate removal of the contamination of thermal emission from the Galactic interstellar dust. The MKID arrays (138 MKIDs for 145GHz and 23 MKIDs for 220GHz) were designed and optimized so as to minimize the contamination of the two-level-system noise and maximize the sensitivity. The MKID arrays were successfully installed in May 2023 after the performance verification tests were performed at a laboratory. GroundBIRD has been upgraded to use the full MKID arrays, and scientific observations are now underway. The telescope is automated, so that all observations are performed remotely. Initial validations, including polarization response tests and observations of Jupiter and the moon, have been completed successfully. We are now running scientific observations.

Sub-mm and mm wavelengths provide a unique view of the Universe, from the gas and dust that fills and surrounds galaxies to the chromosphere of our own Sun. Current single-dish facilities have presented a tantalising view of the brightest (sub-)mm sources, and interferometers have provided the exquisite resolution necessary to analyse the details in small fields, but there are still many open questions that cannot be answered with current facilities: Where are all the baryons? How do structures interact with their environments? What does the time-varying (sub-)mm sky look like? In order to make major advances on these questions and others, what is needed now is a facility capable of rapidly mapping the sky spatially, spectrally, and temporally, which can only be done by a high throughput, single-dish observatory. An extensive design study for this new facility is currently being undertaken. In this paper, we focus on the key science drivers and the requirements they place on the observatory. As a 50m single dish telescope with a 1–2° field of view, the strength of the Atacama Large Aperture Submillimeter Telescope (AtLAST) is in science where a large field of view, highly multiplexed instrumentation and sensitivity to faint large-scale structure is important. AtLAST aims to be a sustainable, upgradeable, multipurpose facility that will deliver orders of magnitude increases in sensitivity and mapping speeds over current and planned telescopes.

Past millimeter-wave galaxy surveys have probed the brightest starburst galaxies only and suffered heavily from confusion. The interpretation of existing surveys has also been hindered by the lack of reliable redshift indicators for measuring distances for the entire sample. Thanks to recent advances in mm-wave detector technologies we can now overcome these limitations, and conduct the first truly volumetric surveys of star-forming galaxies at mm-wavelengths down to the L_∗ luminosities of typical galaxies, with ∼1000 redshift slices spanning most of the Cosmic star-forming volume (z∼1–12) with nearly uniform mass and luminosity selection. We describe an instrument concept capable of delivering such surveys with the technologies available today, which can be built and operated on a ground-based mm-wave facility in the near future. Such spectrometer cameras can resolve and redshift identify up to to 25,000 star-forming galaxies per year even when operated on a 10-m class telescope. On a larger aperture it can do the same faster or probe even deeper. We propose a loose, open-source collaboration to design, build, and operate one or several such cameras through the shared contributions of leading experts and telescopes from around the globe.

Traditional methods of converting electronic readout counts to optical power incident on Transition Edge Sensors (TES) for Cosmic Microwave Background (CMB) observations involve a linear approximation. For the upcoming LiteBIRD CMB satellite, strict nonlinearity requirements must be met to prevent contamination of the science band at 4ƒ_HWP by the 2ƒ_HWP signal, which arises from differential transmission or emissivity related to the half-wave plate’s rotation rate ƒ_HWP. These constraints cannot be met using hardware solutions alone and therefore require a form of nonlinearity correction. We present MNTES, a novel physics-based, nonlinear calibration technique. This method leverages our physical understanding of the TES power balance equation, accounts for imperfect voltage bias by casting the bias network as its Thévenin equivalent, and can incorporate external information such as time-varying magnetic fields and focal plane temperature variations. The detector-specific parameters of MNTES will be measured during the ground calibration campaign prior to the LiteBIRD launch, yielding conversion functions that can take raw time-ordered data and output the reconstructed incident optical power. MNTES will allow us to achieve LiteBIRD’s goal of measuring the primordial tensor fluctuation spectrum to δr < 0.001.

The Millimeter Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs (MISTRAL) is a new high resolution, wide field-of-view camera that was successfully installed in May 2023 at the Sardinia Radio Telescope (SRT). SRT is a 64m fully steerable gregorian radio telescope, and it underwent an upgrade funded by a National Operational Program (PON) with the aim to expand the fleet of receivers of the radio telescope in order to cover frequency up to the W–band. The W-band sky has been extensively studied by Cosmic Microwave Background experiments, both ground-based (ACT, SPT) and satellite-based (WMAP, Planck). However, their resolution is limited to ≈1′ from ground telescopes and ≈10′ from satellite at best. With this new instrument, we aim to map the microwave sky at a resolution of ≈12′′, a capability only shared by few instruments in the world, unlocking the exploration of a plethora of science cases from the recently upgraded SRT. The heart of MISTRAL is a ≈90mm silicon focal plane populated with 415 cryogenic Lumped Elements Kinetic Inductance Detectors (LEKIDs). These detectors are copuled with the telescope using a cold (4K) re-imaging optical system, producing a diffraction limited field-of-view of 4 ′. The system is enclosed in a custom, four stage cryostat, built with strict requirements on its size, in order to fit on the rotating turret that allows to switch the receivers to be quickly moved in and out of the gregorian focus position. The sub-K stage cools the detectors down to 200-240 mK. MISTRAL is now installed on the gregorian focus of SRT and is undergoing the technical commissioning, and will soon enter the scientific commissioning phase. In this contribution we will survey the subsystems of MISTRAL and their performance at the focus of the radio telescope, and report the current status of the technical commissioning.

We present the development of a breadboard model achromatic half-wave plate (AHWP) for the LiteBIRD Low-Frequency Telescope (LFT). LiteBIRD is a JAXA-led strategic L-class satellite mission to probe the cosmic microwave background polarization. The breadboard model (BBM) polarization modulator unit (PMU) of the LFT uses an AHWP, which achieves an observational frequency coverage 34-161 GHz using a five-layer sapphire stack with a diameter of 330 mm based on the Pancharatnam recipe. The sub-wavelength structures on both end surfaces mitigate the reflection over broadband frequencies. The designed single sapphire plate thickness is 4.95 mm, with a corresponding half-wave shift center frequency of 97.5 GHz. We use hydro-catalysis bonding to glue the sapphire surfaces and assemble the five-layer AHWP. The AHWP is successfully assembled and measured. The transmittance and polarization properties are consistent with the theoretical prediction that neglects the effect of the bonding interfaces. In this work, we present the AHWP design, the assembly process, and the polarimetric characterization. We also discuss the path-forward for this BBM AHWP including the cryogenic and vibrational tests, and the development plan for the flight-size engineering model.

We have obtained NASA funding to build and demonstrate Transition Edge Sensor (TES) based kilopixel arrays with the properties that match the requirements for cryogenic far-infrared space missions: the arrays are very closely tileable in one direction and have only a moderate gap in the other direction. This array architecture can meet the sampling- and pixel number requirement of ~ 104 pixels. Many details of the architecture have already been demonstrated individually, and the detector board will be optimized for the use of the latest cryogenic bump bonded NIST 2-D time domain SQUID readout multiplexers with a high density fanout scheme. Additionally, we use flex-lines that are very similar to those developed at Princeton University for the ACT project. We already have a pixel design that exceeds the continuum sensitivity requirements for a cryogenic space mission.

The MISTRAL instrument is a cryogenic, W-band camera consisting of 415 lumped element kinetic inductance detectors. In a significant milestone achieved in May 2023, MISTRAL was successfully installed at the Gregorian focus of the Sardinia Radio Telescope, a 64m aperture telescope in Italy. MISTRAL has a focal plane of ~ 94mm in diameter, resulting in an instantaneous field of view ~ 4 arcmin. To preserve the high angular resolution of the telescope, which is ~ 12 arcsec, the focal plane sampling has been tuned to 4.2 mm, corresponding to a pixel separation of ~ 10.6 arcsec. The remarkable combination of high angular resolution and wide instantaneous field of view makes MISTRAL an exceptionally versatile tool for continuum surveys of wide areas of the sky. Its unique capabilities significantly enhance the observational capacity of the Sardinia Radio Telescope. The lumped element kinetic inductance detectors of MISTRAL are obtained from a titanium-aluminum bilayer 10 + 30nm thick on a single 100 mm–diameter Silicon wafer with thickness 235 μm. They exhibit a critical temperature of 945mK and are optimized to operate within the temperature range of 200 to 240 mK. The feedline is made of an aluminum 21nm thick and has a critical temperature of 1.35 K. We discuss the design, electrical, and optical characterization of the detector array, placing specific emphasis on the yield, the pixel identification on the array, the optical performance, and the calibration procedures.

The PRobe far-Infrared Mission for Astrophysics (PRIMA) is a future cryogenic space observatory that will revolutionize study of evolving galaxies and forming planetary systems with highly-sensitive far-infrared (far-IR) imaging and spectroscopy. PRIMA’s spectrometer, the Far-InfraRed Enhanced Survey Spectrometer (FIRESS), will deploy kilo-pixel aluminum kinetic inductance detector (KID) arrays covering wavelengths from 24-235 μm. Here we present optical characterization of a prototype FIRESS array operating at 25 μm. We employ a blackbody modulation technique to measure the detector responsivity, and discuss methods for reducing 1/f noise from the multi-tone readout electronics. We measure an NEP below 3.5 × 10⁻²⁰ W/ √ Hz at 10 Hz accross the array, which exceeds the requirement to be limited by the astrophysical background limit for PRIMA’s FIRESS spectrometer. We discuss limitations of the multi-tone readout and compare results to measurements with a single-tone readout system.

We used laser ablation to fabricate sub-wavelength structure anti-reflection coating (SWS-ARC) on a 5 cm diameter alumina lens. With an aspect ratio of 2.5, the SWS-ARC are designed to give a broad-band low reflectance response between 110 and 290 GHz. SWS shape measurements give 303 μm pitch and total height between 750 and 790 μm height, matching or exceeding the aspect ratio design values. Millimeter-wave transmittance measurements in a band between 140 and 260 GHz show the increase in transmittance expected with the ARC when compared to finite element analysis electromagnetic simulations. To our knowledge, this is the first demonstration of SWS-ARC on an alumina lens, opening the path for implementing the technique for larger diameter lenses.

We have created and demonstrated a Virtually Imaged Phased Array (VIPA) device for velocity resolved spectroscopy in the far-IR and will present the first cryogenic (LHe) measurements of the spectral profile of a prototype VIPA at 115.7 µm. A VIPA is a compact spectral filter without moving parts that consists of a resonating cavity that generates angular dispersion due to constructive interference, and that can deliver an instantaneous spectrum with a resolving power of 100,000 or more. Coupled with superconducting direct detection detectors, the VIPA promises unsurpassed sensitivity at velocity resolutions > 3 km/s, making it a prime choice for spectroscopic instruments to observe e.g. protoplanetary disks to trace the gaseous building blocks out of which planets form. Due to their compactness and absence of moving parts, VIPAs are optimal for balloon and space-borne astronomical instruments like the NASA Pioneer Mission POEMM and the proposed NASA Probe Mission FIRSST. The prototype we have measured was made of a 3 × 5 × 1 cm block of high-purity float-zone silicon. The entrance and exit sides of the VIPA are highly parallel, and the entrance side was fully metallized (gold-coated) except for a narrow entrance slit resulting in a reflectivity of 100%, while the exit side was metallized with an inductive mesh resulting in a reflectivity of about 88%. The measurement was done using a custom testbed that included separate cryostats for a cryogenically cooled THz Quantum Cascade Laser (QCL) and the VIPA, as well as a warm pyroelectric detector. The QCL was tuned to a number of different frequencies near 2.59 THz and the detector was scanned along the dispersion direction. Our VIPA prototype achieved the designed resolving power of 15,000 and the spectral profile matched extremely well with the expectations from our simulations. We are now building a full testbed to straightforwardly measure and characterize VIPAs and other GHz/THz filters with resolving powers of order 100,000 using tuneable THz lasers.

Unveiling the emergence and prevalence of massive/bright galaxies during the epoch of reionization and beyond, within the first 600 million years of the Universe, stands as a pivotal pursuit in astronomy. Remarkable progress has been made by JWST in identifying an immense population of bright galaxies, which hints at exceptionally efficient galaxy assembly processes. However, the underlying physical mechanisms propelling their rapid growth remain unclear. With this in mind, millimeter and submillimeter-wave spectroscopic observations of redshifted far-infrared spectral lines, particularly the [Oiii] 88 μm and [Cii] 158 μm lines, offers a crucial pathway to address this fundamental query.

To this end, we develop a dual-polarization sideband-separating superconductor-insulator-superconductor (SIS) mixer receiver, FINER, for the Large Millimeter Telescope (LMT) situated in Mexico. Harnessing advancements from ALMA’s wideband sensitivity upgrade (WSU) technology, FINER covers radio frequencies spanning 120–360 GHz, delivering an instantaneous intermediate frequency (IF) of 3–21 GHz per sideband per polarization, which is followed by a set of 10.24 GHz-wide digital spectrometers. At 40% of ALMA’s light-collecting area, the LMT’s similar atmospheric transmittance and FINER’s 5 times wider bandwidth compared to ALMA culminate in an unparalleled spectral scanning capability in the northern hemisphere, paving the way for finer spectral-resolution detection of distant galaxies.

For a high-frequency radio interferometry system such as ngVLA (next generation Very Large Array, receiving frequency is up to 116 GHz), the distribution of a high-frequency reference signal can be advantageous, in that the local oscillator (LO) phase drift associated with frequency multiplication at each remote antenna is minimized. The reference frequency signal is transmitted from a reference station to each antenna as a beat signal of dual-wavelength lightwave signal generated using a high-extinction-ratio Mach-Zehnder modulator. Radio interferometers require correlation processing and signal integration to observe extremely weak radio sources. Atmospheric scintillation correction is also performed, particularly in high-frequency observations. We propose phase compensation for the frequency transmission by offline processing as the same with atmospheric phase scintillation correction. Off-line compensation has advantages with respect to the cost-effectiveness of phase compensation and feedback bandwidth concerns that depend on the delay of the phase-locked loop, including transmission lines. In our fiber transmission scheme, the method measures the double difference phases between the phases before and after the roundtrip of the two lightwaves. Particularly characteristic is that the roundtrip phase of each lightwave of the dual-wavelength signal is measured independently, which provides accurate compensation for chromatic dispersion. Experiments were conducted of 100-GHz reference frequency transmission over optical fiber spools up to 400 km. Additionally, we made frequency transfer experiments using the installed fiber link and the fiber installed in the driving antenna. Based on the results, we will report on the application possibilities and limitations of the proposed dual-wavelength frequency transfer scheme.

We have demonstrated three 4×2 hot electron bolometer (HEB) mixer arrays for operation at local oscillator (LO) frequencies of 1.4, 1.9 and 4.7 THz, respectively. These arrays consist of spiral antenna coupled NbN HEB mixers combined with elliptical lenses. These are to date the highest pixel count arrays using a quasi-optical coupling scheme at supra-THz frequencies. At 1.4 THz, we obtained an average double sideband mixer noise temperature of 330 K, a mixer conversion loss of 5.2 dB, and an optimum LO power of 210 nW. The array at 1.9 THz has an average mixer noise temperature of 425K, a mixer conversion loss of 6.4 dB, and an optimum LO power of 190 nW. For the array at 4.7 THz we obtained an average mixer noise temperature of 715 K, a mixer conversion loss of 8.9 dB, and an optimum LO power of 240 nW. We found the arrays to be uniform regarding the mixer noise temperature with a standard deviation of 3-4%, the conversion loss with a standard deviation of 8-11%, and optimum LO power with a standard deviation of 5-6%. The noise bandwidth was also measured, being 3.5 GHz for the three arrays. These performances are comparable to previously reported values in the literature for single pixels and also other detector arrays at similar frequencies. Our arrays met the requirements and were employed in the Galactic/Extra-Galactic ULDB Spectroscopic Terahertz Observatory (GUSTO), a NASA balloon borne observatory. GUSTO launched from Antarctica on the 31st December 2023 having a successful flight of 57 days, the longest ever recorded by NASA for such mission profile.

Spectroscopic observations of the far-infrared [Oiii] 88 μm and [Cii] 158 μm lines present a pathway to explore the mechanisms of the emergence of massive galaxies in the epoch of reionization and beyond, which is one of the most fundamental questions in astronomy. To address this question, the Far-Infrared Nebular Emission Receiver (FINER) project is developing two wideband dual-polarization sideband-separating heterodyne receivers at 120–210 GHz and 210–360 GHz for the Large Millimeter Telescope (LMT) in Mexico. Compared with Atacama Large Millimeter/submillimeter Array (ALMA), LMT provides 40% of ALMA’s light-collecting area and a similar atmospheric transmittance, but FINER plans to have an instantaneous intermediate frequency (IF) of 3–21 GHz per sideband per polarization which is five times wider than current ALMA’s bandwidth. Therefore, FINER is going to offer cutting-edge spectral scanning capability in the next several years.

The project is currently in an active development phase. In this proceeding, the latest development status for FINER, including the optics, wideband waveguide components as well as low-noise superconductor-insulator-superconductor (SIS) mixers is reported.

The Atacama Large Millimeter/submillimeter Array (ALMA) Wideband Sensitivity Upgrade (WSU) will at least double the observation bandwidth and improve the sensitivity and scientific capabilities. The WSU requires upgrading the receiver front-end and the associated analog and digital electronics including the correlator, as well as the ALMA software. In line with the WSU mission, the National Astronomical Observatory of Japan (NAOJ) initiated the ALMA Band 8 (385-500 GHz) version2 receiver upgrade project, aiming to build an upgrade of the currently existing receiver cartridge with a substantially improved second-generation version. This project originated from significant advances in receiver technologies and a variety of our previous wideband studies in the last decade. This paper briefly summarizes an overview of this project, scientific needs in this frequency range, and the technical readiness and challenges for critical components and subsystems.

This paper introduces a potential low-power-consumption and low-noise microwave amplifier operated at cryogenic temperature, essential for large-scale multi-pixel heterodyne receivers and fault-tolerant quantum computers. The amplifier employs two millimeter-wave superconductor-insulator-superconductor (SIS) mixers as amplifying elements and a millimeter-wave Josephson array oscillator as the local oscillator source. A proof-of-concept experiment utilizing waveguide SIS mixer modules demonstrated an average gain of approximately 7.5 dB and a noise temperature of around 10 K at microwave frequencies. Additionally, a waveguide Josephson array oscillator module, developed to validate the design, exhibited an output power of roughly 52 nW, estimated from the response of a waveguide SIS detector connected to the oscillator module. These findings indicate the feasibility of realizing a monolithically integrated amplifier chip incorporating SIS mixers and a Josephson array oscillator.

The idea of ALMA Band-4+5 receivers are proposed for the upgrade after 2030. The new receiver will cover the RF frequency of the original Band-4 and Band-5 with continuous frequency tuning over 125 –211 GHz with dual polarizations, dual sidebands capability. The instantaneous intermediate frequency (IF) bandwidth is up to 16 GHz per sideband and per polarization. Both the SIS-based receiver and HEMT-based receiver schemes are considered. For the SIS receiver scheme, the niobium-based SIS junctions will be fabricated to form mixer chips, and integrated into the mixer blocks with broadband waveguide 3-dB quadrature hybrid couplers with LO couplers, cryogenic IF low-noise amplifiers, and 2-20 GHz coaxial 3-dB quadrature hybrid couplers to form sideband separating down-converters. The inputs of the sideband separating down-converters are fed by the ellipsoidal mirror pairs, corrugated feedhorn and the orthomode transducer. For the HEMT-based receiver scheme, using the same optics configuration as the SIS-based receiver, the cryogenic InP HEMT low-noise amplifiers (LNAs) chains cover 125 – 211 GHz operated in 15-K ambient temperature will be the key components of the cold cartridge assembly (CCA). For the warm cartridge assembly, a pair of sideband-separating diode or resistive transistor mixers will provide four-channel 16-GHz IF instantaneous bandwidth. To avoid the possible interference between LO and IF signals, considering the possible 16 GHz IF bandwidth over 4 – 20 GHz, the LO fundamental frequency will be chosen in 24 - 32 GHz, followed by an active frequency tripler to form the phase-lock loop with 72 – 96 GHz frequency tuning range. The key components with 51.2% relative bandwidth to be developed in-house are Nb SIS mixers, RF InP HEMT LNAs, 3-dB waveguide hybrid couplers, orthomode transducers, corrugated horn antenna, and optics mirror pairs.

The BISOU (Balloon Interferometer for Spectral Observations of the primordial Universe) project studies the viability and prospects of a balloon-borne spectrometer, pathfinder of a future space mission dedicated to the measurements of the CMB spectral distortions. A balloon concept based on a Fourier Transform Spectrometer, covering a spectral range from about 90 GHz to 2 THz, adapted from previous mission proposals such as PIXIE and FOSSIL, is being studied and modeled. Taking into account the requirements and conditions of balloon flights, we present here the instrument concept together with the results of a CNES Phase 0 study. We forecast a first detection of the CMB Compton y-distortion monopole with a signal-to-noise ratio of at least 5. We also present the future plan and work that will be the subject of a recently awarded two-year Phase A study.

Modern astrophysics relies on intricate instrument setups to meet the demands of sensitivity, sky coverage, and multi-channel observations. An example is the CONCERTO project, employing advanced technology like kinetic inductance detectors and a Martin-Puplett interferometer. This instrument, installed at the APEX telescope atop the Chajnantor plateau, began commissioning observations in April 2021. Following a successful commissioning phase that concluded in June 2021, CONCERTO was offered to the scientific community for observations, with a final observing run in December 2022. CONCERTO boasts an 18.5 arcmin field of view and a spectral resolution down to 1.45 GHz in the 130–310 GHz electromagnetic band. We developed a comprehensive instrument model of CONCERTO inspired by Fourier transform spectrometry principles to optimize performance and address systematic errors. This model integrates instrument noises, subsystem characteristics, and celestial signals, leveraging both physical data and simulations. Our methodology involves delineating simulation components, executing on-sky simulations, and comparing results with real observations. The resulting instrument model is pivotal, enabling a precise error correction and enhancing the reliability of astrophysical insights obtained from observational data. In this work, we focus on the description of three white-noise noise components included in the instrument model that characterize the white-noise level: the photon, the generation-recombination, and the amplifier noises.

In the effort to push the boundaries of radio astronomy observations, technological innovations are essential for future generations of observatories. This paper introduces an innovative design for future radio receivers in major observatories like ngVLA, ALMA, and SKA. The concept centers around an Octave Band Quad Ridge Feed Horn and Vacuum Window, designed to operate within the 25 to 50 GHz (2:1) frequency range. This cutting-edge feed model uses dielectric loading to enhance phase and polarization efficiency, thereby significantly increasing the overall aperture efficiency across the bandwidth. The dielectric rod, features a solid construction with comb-shaped ridges located in the throat of the feed horn. To complete the entire optic model an HDPE vacuum window with three custom designed antireflection layers to minimize the signal reflections, is designed and presented. To confirm the performance of the proposed model, we use two different 3D full-wave electromagnetic simulators, CST Studio Suite and HFSS. The results showcase a return loss exceeding 25dB with exceptional beam symmetry across the entire bandwidth.

RF-ICE is a signal processing platform for the readout of large arrays of superconducting resonators. Designed for flexibility, the system’s low digital latency and ability to independently and dynamically set the frequency and amplitude of probe tones in real time has enabled previously-inaccessible views of resonator behaviour, and opened the door to novel resonator control schemes. We introduce a multi-frequency imaging technique, developed with RF-ICE, which allows simultaneous observation of the entire resonance bandwidth. We demonstrate the use of this technique in the examination of the response of superconducting resonators to variations in applied readout current and thermal loading. We observe that, used in conjunction with a conventional frequency sweep at sufficiently large amplitude to induce resonance bifurcation, the multi-frequency imaging technique reveals a resonator response which is not captured by the frequency sweep measurement alone. We demonstrate that equivalent resonant frequency shifts can be achieved using either thermal, optical, or readout loading, and use this equivalence to counteract a change in thermal loading by digitally modulating the readout current through a resonator. We develop and implement a proof-of-concept closed-loop negative electro-quasiparticle feedback algorithm which first sets and then maintains the resonant frequency of a lumped element kinetic inductance detector while the loading on it is varied. Although this simple implementation is not yet suitable to deploy at scale, it demonstrates the utility of this feedback technique to improve linearity while addressing amplifier distortion, resonator response non-uniformity, and crosstalk. It can be applied to kinetic inductors in non-bolometric operation, and sets the stage for future developments.

The t0.technology Control and Readout System (CRS) is a modular microwave control and readout system for mm-wave and radio astronomy, THz imaging, noise radar, and superconducting qubit control. The configuration discussed in this work implements firmware for readout of microwave Kinetic Inductance Detector (KID) arrays. The CRS can operate 4,096 KIDs over 2.5 GHz of complex bandwidth between 0–10 GHz, typically allocated across four independent RF chains at 1,024x multiplexing and 625MHz of complex bandwidth each. Every CRS can operate as a standalone unit or collectively within one or more backplane-enabled subracks that distribute power, clocking, and synchronization, scaling to an arbitrary number of channels. Each fully populated subrack supports arrays of more than 65,000 KIDs. The signal processing and control software supports recent innovations in multi-probe measurements and dynamic feedback modes, which are described in Rouble et al. (2024, these proceedings). The CRS has recently been selected as the new baseline readout system for the proposed South Pole Telescope instrument, SPT-3G+.¹ We present the hardware design, firmware capabilities, open-source control and data acquisition software, and the first laboratory characterization measurements.

Future far-infrared (FIR) astronomy missions will need large detector arrays with high sensitivity. Low noise detectors with a noise equivalent power (NEP) of 3×10⁻¹⁹ to 1×10⁻²⁰ W/Hz1/2 for space-based continuum observations are needed, to be photon noise limited. Transition edge sensor (TES) as a type of sensitive low-temperature superconducting detector, has significant advantages in the measurement of broad band electromagnetic radiation, from millimeter waves to X-ray and gamma-rays. We propose a design of low noise TESs for FIR applications, with the NEP of lower than 3×10⁻¹⁹ W/Hz^1/2. The key component on TES bolometer island is aluminum-manganese (AlMn) superconducting film, which has been proved that its critical temperature can be adjusted over a wide range by baking after the film deposition. We optimize the NEP of AlMn TESs by reducing the critical temperature to around 60 mK and designing the thermally isolating legs to reduce the thermal conductance effectively. The pixel design will be used as foundation in our future TES array designs and will benefit high-sensitive detector development.

OLIMPO is a 2.6m balloon–borne telescope intended to observe, with high–angular resolution, the millimeter and sub–millimeter sky from the Antarctic stratosphere. It will allow us to study the dynamics of galaxy cluster formation and to characterize the intergalactic medium up to the cluster outskirt through the Sunyaev-Zel’dovich effect. OLIMPO utilizes four arrays of kinetic inductance detectors (KIDs), in the 145, 250, 350 and 460 GHz bands, operated at about 300 mK. OLIMPO has already flown, in a technological flight, in 2018 from Svalbard, Norway, proving for the first time that KIDs are capable to withstand the demanding conditions on high altitude balloons. KIDs are superconducting, low–temperature detectors suited for this kind of applications due to their intrinsic capability to be frequency–domain multiplexed, enabling very high–sensitivity sky surveys. In this work, we present the design, optimization and laboratory characterization of the 313–pixel array for the OLIMPO 350 GHz frequency band. We showcase results of the electrical characterization (electrical responsivity and the measurement of the quasiparticle lifetime) and the optical characterization (optical responsivity and optical efficiency) accomplished with a 4K cooled black body.

The Epoch of Reionization Spectrometer (EoR-Spec) is an upcoming Line Intensity Mapping (LIM) instrument designed to study the evolution of the early universe (z = 3.5 to 8) by probing the redshifted [CII] 158 μm fine-structure line from aggregates of galaxies. The [CII] emission is an excellent tracer of star formation since it is the dominant cooling line from neutral gas heated by OB star light and thus can be used to probe the reionization of the early Universe due to star formation. EoR-Spec will be deployed on Prime-Cam, a modular direct-detection receiver for the 6-meter Fred Young Submillimeter Telescope (FYST), currently under construction by CPI Vertex Antennentechnik GmbH and to be installed near the summit of Cerro Chajnantor in the Atacama Desert. This instrument features an image plane populated with more than 6500 Microwave Kinetic Inductance Detectors (MKIDs) that are illuminated by a 4-lens optical design with a cryogenic, scanning Fabry-Perot Interferometer (FPI) at the pupil of the optical system. The FPI is designed to provide a spectral resolving power of R ∼ 100 over the full spectral range of 210–420 GHz. EoR-Spec will tomographically survey the E-COSMOS and E-CDFS fields with a depth of about 4000 hours over a 5 year period. Here we give an update on EoR-Spec’s final mechanical/optical design and the current status of fabrication, characterization and testing towards first light in 2026.

For efficient spectroscopic redshift identification of early galaxies in the northern hemisphere, we aim to combine the Large Millimeter Telescope (LMT) with a wide-band heterodyne receiver, FINER, which will cover radio frequencies of 120–360 GHz and offer a 3–21 GHz intermediate frequency (IF) per sideband and polarization. To take full advantage of such wide IFs, we present a novel 10.24-GHz-wide digital spectrometer, DRS4 (Elecs Industry Co., Ltd.). It incorporates 20.48 Gsps samplers with an FPGA-based digital signal processing module. To mitigate the noise contamination from the image sideband, it is equipped with a digital sideband separation function to improve the sideband rejection up to 25 dB. Laboratory performance evaluations show that it exhibits an Allan time of at least ~ 100 s and a total power dynamic range of at least 7 dB. These results demonstrate its capability of instantaneously wide-band spectroscopy toward high-redshift galaxies with position-switching observations.

The goal of the PolarKID project is testing a new method for the measurement of polarized sources, in order to identify all the possible instrumental systematic effects that could impact the detection of CMB B-modes of polarization. It employs the KISS (KIDs Interferometer Spectrum Survey) instrument coupled to a sky simulator and to sources such as point-like black bodies (simulating planets), a dipole (extended source) and a polarizer. We use filled-arrays Lumped Element Kinetic Inductance Detectors (LEKIDs) since they have multiple advantages when observing both in a photometry and in a polarimetry configuration.

The Simons Observatory (SO) is a ground-based experiment aiming to enhance our understanding of the early universe, by making detailed measurements of the cosmic microwave background (CMB), across multiple spectral bands ranging from 30 to 280 GHz. The baseline project in the Atacama Desert in Chile, comprises four small-aperture telescopes (SATs) and one large-aperture telescope (LAT), housing a total of 60,000 detectors with angular resolutions ranging from 1-90 arc-minute. The low frequency detector arrays to be deployed in the LAT, feature anti-reflection (AR) coated lenslet-coupled sinuous antennas with a diplexing filter for the 30 and 40 GHz bands centers. Superconducting niobium (Nb) microstrip lines carry the signal for each polarization and band to titanium (Ti) load resistors which in turn heat up palladium (Pd) thermal ballasts and are sensed with transition edge sensors (TESs). The TESs are constructed from aluminum manganese (AlMn) and operate in their superconducting transitions (T_c) with a base temperature of 100mK. The sensors are read out by cryogenic microwave resonators using RF superconducting quantum interference devices (SQUIDs) in the microwave multiplexing (uMux) scheme. In these proceedings, we report on the current status of design, fabrication and characterization of the Simons Observatory low frequency detectors fabricated by UC Berekeley. The fabricated detector arrays have an average bolometer yield of 94% and desirable radio frequency (RF) characteristics.

LiteBIRD, a forthcoming JAXA mission, aims to accurately study the microwave sky within the 40-400 GHz frequency range divided into 15 distinct nominal bands. The primary objective is to constrain the CMB inflationary signal, specifically the primordial B-modes. LiteBIRD targets the CMB B-mode signal on large angular scales, where the primordial inflationary signal is expected to dominate, with the goal of reaching a tensor-to-scalar ratio sensitivity of σr ∼ 0.001. LiteBIRD frequency bands will be split among three telescopes, with some overlap between telescopes for better control of systematic effects. Here we report on the development status of the detector arrays for the Low Frequency Telescope (LFT), which spans the 34-161 GHz range, with 12 bands subdivided between four types of trichroic pixels consisting of lenslet-coupled sinuous antennas. The signal from the antenna is bandpass filtered and sensed by AlMn Transition-Edge Sensors (TES). We provide an update on the status of the design and development of LiteBIRD’s LFT LF1 (40-60-78 GHz), LF2 (50-68-89 GHz) pixels. We discuss design choices motivated by LiteBIRD scientific goals. In particular we focus on the details of the optimization of the design parameters of the sinuous antenna, on-chip bandpass filters, cross-under and impedance transformers and all the RF components that define the LF1 and LF2 pixel detection chain. We present this work in the context of the technical challenges and physical constraints imposed by the finite size of the instrument.

This work deals with the development of superconducting Kinetic Inductance Detectors (KIDs) for highly sensitive radio astronomy receivers within W-band (75 to 110 GHz). A bilayer based on superconducting titanium/aluminum (Ti/Al) thin films has been used for assessing its absorption performance in this frequency band at millikelvin temperature. A lumped-element inductor based on a 4th order Hilbert structure is designed to absorb the incoming radiation in two orthogonal linear polarizations. The development of a large-format camera prototype is presented. On one hand, ambient temperature quasi-optical characterization demonstrates a suitable absorption for both polarizations within the W-band. On the other hand, dark cryogenic characterization confirms the successful operation of the multiplexed KID devices providing high-quality factors and an operation yield of 97%. These results confirm these developments to be used in future polarimeter receivers.

Double-Fourier interferometry (DFI) from a space-based platform provides a path to achieve broadband imaging spectroscopy in the far-infrared with sub-arcsecond angular resolution. To provide further study of the technique and improve its technology readiness, we have constructed a laboratory-based DFI testbed. This instrument is coupled to a custom array of 25 feedback-controlled transition-edge sensor (TES) bolometers. We present the results of characterisation experiments to optimise the detector system as an integrated component of the DFI assembly. We demonstrate that tuning the proportional-integral-derivative (PID) feedback control loops of the detectors and the timing of the multiplexed measurement process can modify the detector array’s noise performance and speed of response to optical modulation for this purpose. From these, we have determined a set of optimised detector settings that reduce spectral noise in the spatial-spectral interferometer by 37–79%. In addition, we present further thermal characterisation of the detector array.

The SLAC Microresonator Radio Frequency (SMuRF) electronics is being deployed as the readout for the Cosmic Microwave Background (CMB) telescopes of the Simons Observatory (SO). A Radio Frequency System-on-Chip (RFSoC) based readout of microwave frequency resonator based cryogenic sensors is under development at SLAC as an upgrade path for SMuRF with simplified RF hardware, a more compact footprint, and lower total power consumption. The high-speed integrated data converters and digital data path in RFSoC enable direct RF sampling without analog up and down conversion for RF frequencies up to 6 GHz. A comprehensive optimization and characterization study has been performed for direct RF sampling for microwave SQUID multiplexers, which covers noise level, RF dynamic range, and linearity using a prototype implementation. The SMuRF firmware, including the implementation of closed-loop tone tracking, has been ported to the RFSoC platform and interfaced with the quadrature mixers for digital up and down conversion in the data converter data path to realize a full microwave SQUID multiplexer readout. In this paper, a selection of the performance characterization results of direct RF sampling for microwave SQUID multiplexer readout will be summarized and compared with science-driven requirements. Preliminary results demonstrating the read out of cryogenic sensors using the prototype system will also be presented here. We anticipate our new RFSoC-based SMuRF system will be an enabling readout for on-going and future experiments in astronomy and cosmology, which rely on large arrays of cryogenic sensors to achieve their science goals.

ASTHROS (Astrophysics Stratospheric Telescope for High Spectral Resolution Observations at Submillimeter-wavelengths) is a high-altitude balloon mission utilizing an array of sixteen spectrometers to create high spatial resolution 3D maps of ionized nitrogen gas in galactic and extragalactic star-forming regions. During data collection, we utilize on-the-fly mapping, where the instrument continuously collects spectra while scanning over a target area. After a sweep across the target, we take a calibration spectra to correct our science data. These calibration spectra provide a baseline for how the instrument is operating at a given moment. As we collect new calibration spectra, we can compare the current calibration with a series of past calibrations to determine if our system is producing anomalous spectra. Some examples of anomalous spectra are changes in RFI spike frequency, location, or amplitudes, changes in the overall readout level, and changes in the shape of the spectra. We compare statistical and data-driven methods for detecting these anomalies and evaluate their performance to determine the best fit for the ASTHROS readout system. For data-driven methods, we compare the latent space representation of our calibration spectra with past calibrations using models like Variational AutoEncoders (VAE) and Principal Component Analysis (PCA). By comparing with a rolling window of past calibrations, we allow our system to change gradually while identifying sudden irregularities. When spectra are labeled as anomalous, they are prioritized for review so that the ground operations team can analyze and address the issue. On-board analysis is enabled by the readout system architecture which utilizes the RabbitMQ (RMQ) messaging networking. RMQ allows us to modularly build our readout system and create additional functionality, such as on-board analysis, without making modifications to the operation pipeline.

The next-generation mm/sub-mm/far-IR astronomy will in part be enabled by advanced digital signal processing (DSP) techniques. The Prime-Cam instrument of the Fred Young Submillimeter Telescope (FYST), featuring the largest array of submillimeter detectors to date, utilizes a novel overlap-channel polyphase synthesis filter bank (OC-PSB) for the AC biasing of detectors, implemented on a cutting-edge Xilinx Radio Frequency System on Chip (RFSoC). This design departs from traditional waveform look-up-table(LUT) in memory, allowing real-time, dynamic signal generation, enhancing usable bandwidth and dynamic range, and enabling microwave kinetic inductance detector (MKID) tracking for future readout systems. Results show that the OC-PSB upholds critical performance metrics such as signal-to-noise ratio (SNR) while offering additional benefits such as scalability. This paper will discuss DSP design, RFSoC implementation, and laboratory performance, demonstrating OC-PSB’s potential in submillimeter-wave astronomy MKID readout systems.

LiteBIRD is a JAXA-led spacecraft mission that has the objective of making a full-sky measurement of the CMB polarization B-modes to constrain the tensor-to-scalar ratio r with a sensitivity of σ(r) of 0.001. Its three telescopes will host a total of 4508 Transition-Edge Sensor (TES) bolometers at a temperature of 100 mK. The signal from the thousands of bolometers will be multiplexed using digital frequency-domain multiplexing (DfMux). In DfMux, each TES in a group of up to 68 is assigned to a frequency channel between 1.5 and 5.6 MHz by an inductor-capacitor (LC) chip, and the multiplexed signal is amplified by a Superconducting Quantum Interference Device (SQUID) Array Amplifier (SAA). Both SAA and LC chips will operate at sub-Kelvin temperatures and be mounted to the detector sub-assembly on the side opposite to the sky, in what is here defined as the cold readout sub-assembly. Components of the cold readout sub-assembly will need to withstand large mechanical stress during launch and achieve excellent electronic performance to meet the mission’s requirements. In this work we present the status of the design, prototyping and testing of cold readout sub-assembly components. This includes a measurement of the inductance of custom-made edge-coupled superconducting cables, which were found to be in the order of 0.5 nH/cm. Further, we demonstrate that a rigid-flex PCB could be used to thermally isolate SAAs while maintaining close to 5 nW of heat dissipation between the SAA and the LC temperature stages. Finally, we report on simulations of different magnetic shields that could be used to prevent pickup of environmental magnetic flux by the SAAs and the shields’ comparative effectiveness. The results presented here will be used to guide and predict the performance of the next iterations of the cold readout sub-assembly design for LiteBIRD.

Arrays of transition-edge sensors (TES) with applications from X-ray to FIR-to-mm astronomy can be read out efficiently using frequency domain multiplexing (FDM) readout with baseband feedback. The calibration of the TES/FDM systems is critical in assessing/improving their performance but the calibration is less straightforward than for TES detectors operated under DC bias. We have designed and tested a calibration method based on Johnson noise measurements, assuming good knowledge of the LC filter inductance and temperature. With the calibrated Johnson noise source at the input of our readout, we are able to measure both the open-loop and closed-loop behavior of the system. We applied this method to an 88-pixel TES bolometer array under dark conditions. Our new calibration successfully yields useful instrumental properties including TES normal resistances, feedback impedances, IV curves, power plateaus, and dark NEP. Notably, the resulting saturation power does not appear to depend on the resonance frequency, a desirable feature absent in our previous calibrations, suggesting that our noise-based calibration is robust. This calibration method can be applied to future TES arrays.

The LiteBIRD mission is dedicated to the search for primordial B modes in the Cosmic Microwave Background (CMB) polarization. To achieve unprecedented sensitivity and accuracy in this measurement, the control of instrument systematics is paramount. In this context, we describe the development of microwave absorbers needed to mitigate the straylight within the telescope tubes of the LiteBIRD Mid- and High-Frequency Telescopes (MHFT). A baseline solution has been designed and validated using HFSS simulations, consistently demonstrating sub-percent level specular reflectance across the entire 90-448 GHz band of the MHFT under a broad variety of incidence conditions, representative of the actual optical environment predicted for the two telescopes. Leveraging consolidated technologies, a prototype has been manufactured and characterized in laboratory, demonstrating a promising reflectance mitigation despite the deviation from the nominal geometry. Ongoing parallel efforts involve a comprehensive investigation (both through simulations and laboratory measurements) of the requirements to be finalized in order to define the practical implementation of the baseline design. This activity will ultimately ensure the alignment with allocated thermo-mechanical requirements along with the compliance with the desired electromagnetic performance. The presented studies not only solidify the feasibility of the straylight mitigation approach, but also inform the finalization of the optical tube design, in view of the conclusion of the CNES Phase A study of LiteBIRD.

We present results from efforts to build a drone-based calibration system providing a high-accuracy polarized reference signal for mm-wave telescopes mapping the cosmic microwave background. The multi-rotor drone allows the source to reach the far-field of small aperture telescopes, such as CLASS or SO-SATs, at their nominal elevation angle, providing a reference signal under normal observing conditions. The goal is to achieve calibration accuracy of at least 0.1 degrees on the absolute polarization angle response. Results from three flight campaigns at the CLASS site, Cerro Toco, Chile, tested the on-board metrology system, using GPS and photogrammetry to determine the source’s position and orientation during flight. The results indicate the drone’s position is known within 10 cm and its polarization angle to better than 0.05 degrees, meeting the system’s technical requirements.

We present the design and validation of a variable temperature cryogenic blackbody source, hereinafter called a cold load, that will be used to characterize detectors to be deployed by CMB-S4, the next-generation ground-based cosmic microwave background (CMB) experiment. Although cold loads have been used for detector characterization by previous CMB experiments, this cold load has three novel design features: (1) the ability to operate from the 1 K stage of a dilution refrigerator (DR), (2) a ³He gas-gap heat switch to reduce cooling time, and (3) the ability to couple small external optical signals to measure detector optical time constants under low optical loading. The efficacy of this design was validated using a 150 GHz detector array previously deployed by the Spider experiment. Thermal tests showed that the cold load can be heated to temperatures required for characterizing CMB-S4’s detectors without significantly impacting the temperatures of other cryogenic stages when mounted to the DR’s 1 K stage. Additionally, optical tests demonstrated that external signals can be coupled to a detector array through the cold load without imparting a significant optical load on the detectors, which will enable measurements of the CMB-S4 detectors’ optical time constants.

The Simons Observatory (SO) group of instruments are together pursuing a major step forward in the ground-based study of the Cosmic Microwave Background (CMB). With one 6 m large-aperture telescope and three 0.4 m small-aperture telescopes (SATs), SO will strive to recover faint CMB polarization signals at a wide range of angular scales and across six frequency bands inside of atmospheric transmission windows spanning the range 27 GHz to 280 GHz. The first instrument to record celestial light is the first of two mid-frequency SATs, SAT MF-1, with over 3,000 dichroic pixels sensitive to two frequency bands centered at 90 and 150 GHz. This instrument began observing in October 2023, and features a cryogenically-cooled polarization modulator consisting of a spinning half-wave plate, a set of three silicon lenses with metamaterial anti-reflection coating, and a focal plane of seven modules referred to as universal focal-plane modules (UFMs), each containing 1,720 AlMn transition-edge sensor (TES) bolometers coupled to a 100 mK bath. In this proceedings, we report on initial efforts to calibrate the TES bolometer response to electrical and optical signals and preliminary characterization of possible confounding signals like scan-synchronous pickup. We comment on how these elements pertain to the analysis of systematic errors relating to the ultimate goal of the SO SAT program: the further constraint of the tensor-to-scalar ratio, r, and the possibility of primordial gravitational waves generated in the early universe by a period of inflation.

In this work, we present the design and manufacturing of the two multi-mode antenna arrays of the COSMO experiment and the preliminary beam pattern measurements of their fundamental mode compared with simulations.

COSMO is a cryogenic Martin-Puplett Fourier Transform Spectrometer that aims at measuring the isotropic y-type spectral distortion of the Cosmic Microwave Background from Antarctica, by performing differential measurements between the sky and an internal, cryogenic reference blackbody. To reduce the atmospheric contribution, a spinning wedge mirror performs fast sky-dips at varying elevations while fast, low-noise Kinetic Inductance detectors scan the interferogram.

Two arrays of antennas couple the radiation to the detectors. Each array consists of nine smooth-walled multi-mode feed-horns, operating in the 120−180 GHz and 210−300 GHz range, respectively. The multi-mode propagation helps increase the instrumental sensitivity without employing large focal planes with hundreds of detectors. The two arrays have a step-linear and a linear profile, respectively, and are obtained by superimposing aluminum plates made with CNC milling. The simulated multi-mode beam pattern has a ~ 20° − 26° FWHM for the low-frequency array and ~16° FWHM for the high-frequency one. The side lobes are below −15 dB.

To characterize the antenna response, we measured the beam pattern of the fundamental mode using a Vector Network Analyzer, in far-field conditions inside an anechoic chamber at room temperature. We completed the measurements of the low-frequency array and found a good agreement with the simulations. We also identified a few non-idealities that we attribute to the measuring setup and will further investigate. A comprehensive multi-mode measurement will be feasible at cryogenic temperature once the full receiver is integrated.

The Simons Observatory (SO) is a Cosmic Microwave Background experiment located in the Atacama Desert in Chile. SO consists of three small aperture telescopes (SATs) and one large aperture telescope (LAT) with a total of 60,000 detectors in six frequency bands.¹ As an observatory, SO encompasses hundreds of hardware components simultaneously running at different readout rates—all separate from its 60,000 detectors on-sky and their metadata. We provide an overview of commissioning SO’s data acquisition software system for SAT-MF1, the first SAT deployed to the Atacama site. Additionally, we share insights from deploying data access software for all four telescopes, detailing how performance limitations affected data loading and quality investigations, which led to site-compatible software improvements.

The magnetic field (B-field) plays a crucial role in the process of star formation. To observe molecular cloud B-fields, astronomers rely on submm dust emission observation. This is because dust grains in molecular clouds align with B-field. However, polarized signals are obscured by the intense non-polarized emission from the Earth’s atmosphere. To overcome this challenge, sophisticated instruments (polarimeters) and strategic observation methods are necessary. However, these tools have not undergone fundamental advancements for two decades because new technologies can only be tested on remote and rare submm telescopes. Thus, we are motivated to develop the Sky Noise Simulator (SNoS). Here we present how we use SNoS to produce a beam that consists of predominantly non-linearly polarized noise and a faint linearly polarized signal. This combined beam is then directed into the instrument under test (IUT). With SNoS, polarimeters can be conveniently tested in the laboratory without moving to telescopes.

Magnetic field (B-field) is the most controversial factor in molecular clouds for star formation, necessitating further observations. The Star Formation Group at the Chinese University of Hong Kong is currently engaged in the construction of ROGer, Asia's inaugural polarimetry. ROGer will be installed on the 12-meter Greenland Telescope (GLT) and will facilitate the observation of B-field morphology within molecular clouds by utilizing dust thermal emission at 345 GHz. ROGer's polarization module introduces the novel implementation of Martin-Puplett interferometer (MPI) optics, enabling real-time sky noise elimination on the same detector through destructive interference. Two 157-pixel silicon-based aluminum film Microwave Kinetic Inductance Detector (MKID) arrays will be employed to detect the orthogonal signal from the MPI optics. Here we will present the prototype of our novel MPI polarimetry and optics design.

This study focuses on the radiation performance of a system composed of a room-temperature C-band Phased Array Feed (PAF) illuminating the 64-m diameter Sardinia Radio Telescope (SRT) main reflector from its primary focus (f/D=0.328). The PAF, a square array with 8x8 dual-polarized antennas, is the first version of a prototype designed for radio astronomy applications in the framework of an R&D (Research and Development) project of the Italian National Institute for Astrophysics (INAF). To guarantee high sensitivity and low noise temperature, the PAF elements have been designed for an optimum coupling with the SRT main reflector by trading off between maximizing the illumination efficiency and minimizing the spillover. In this paper, first, we present the results of the electromagnetic simulation of the PAF element radiation patterns in the Far Field (FF) region, both by assuming no interaction with the reflector and by taking into account the reflection from the SRT main reflector primary focus; second, we present the performance of the beamformed patterns obtained by applying two different beamforming methods; finally, we assess the aperture blockage effect due to the SRT sub-reflector. Results are shown at three frequencies within the operative band of the C-band PAF, i.e. at 4.5, 5.5 and 6.0 GHz.

The Africa Millimetre Telescope (AMT) is a project to realize the first millimeter-wave telescope in Namibia desert to participate in the Event Horizon Telescope (EHT) network and make higher-resolution pictures of black holes possible. We made a preliminary design of the optics to combine the beams of the first light receivers that will enable simultaneous observations of the same area of the sky in four frequency bands. The system is based on the use of dichroics and it has been designed following a geometrical optics approximation to guarantee that all beams will follow the same optical path.

The Lunar Surface Electromagnetics Experiment at Night (LuSEE-Night) is a project designed to investigate the feasibility of observing the Cosmic Dark Ages using an instrument on the lunar far-side. LuSEE-Night will measure the redshifted 21 cm transition of neutral hydrogen over a frequency range of 0.1-50 MHz, covering the redshift range 27 < z < 1100. The LuSEE-Night instrument is a radio frequency spectrometer, consisting of four horizontal monopole antennas, arranged to give wide zenith-pointing beams with two orthogonal linear polarizations. This combination of polarization, spectral, and angular sensitivity will be necessary to separate the cosmological signal from significantly stronger foreground emissions. LuSEE-Night will observe in drift scan during lunar night while the moon shields it from radio frequency interference from both the Earth and sun, and will transmit science and telemetry data back to Earth via an orbital relay during the lunar day. LuSEENight will have to operate in a challenging environment: its electronics must operate under hard radiation, the instrument must be thermally isolated during the cold 100 K lunar night, and have a thermal rejection path to survive the 390 K daytime temperature, and its photovoltaic and battery systems must provide sufficient power to operate during two weeks of lunar night. Furthermore, the instrument spectrometer must be powered throughout the lunar night using only a 7 kWh battery, due to mass limitations. Here we describe the power generation, storage, and delivery subsystems of the LuSEE-Night instrument, and the simulations of expected power generation, draw, and reserves over time which were performed in order to design the power subsystems, and ensure instrument survival and operation throughout the long lunar night. We also describe the Concept of Operations (ConOps) developed for the LuSEE-Night mission, which derives from the power management simulations.

A novel wideband orthomode transducer (OMT) featuring a folded-arm turnstile junction covering a 2:1 frequency band is employed to achieve an effective structure while meeting the strict OMT requirements for radio astronomy applications. The turnstile junction is designed with two symmetry planes to ensure separation between perpendicular polarizations and the effective management of higher order modes. Within the throat of the turnstile junction, stepped cylinders serve as scattering elements and matching stubs to ensure efficient impedance matching between the quad-ridge circular waveguide at the input and the single-ridge rectangular waveguides at the output. The folded arms play a pivotal role in achieving excellent matching while significantly reducing the overall size. Considering the significance of developing wideband radio astronomy receivers with minimal noise, this design demonstrates a precisely engineered compact OMT, with tuned bends, junctions, and delivers simulated return loss better than 20 dB while maintaining cross-polarization performance well below 65 dB within the specified 20-40 GHz frequency range.

The axion is a long-postulated boson that can simultaneously solve two crucial problems of Modern Physics: the unexpected charge and parity symmetry observed in the strong nuclear force and the enigma of dark matter. The Dark-photons and Axion- Like particles Interferometer (DALI) is a proposal for a new generation axion detector designed to probe dark matter in a broad band that ranges from microwaves to mm-wave employing a tunable multilayer Fabry-Pérot interferometer. This frequency range remains poorly explored owing to the technological challenges associated with the development of the experimental approach required to scan it. The DALI instrument, which is currently in the prototyping phase, imports technology and techniques from radio astronomy. This apparatus may also be sensitive to other hypothetical particles, such as the dark photon.

A resonator is needed to enhance the weak signal originating from axion to photon conversion by the action of an external magnetic field. It is composed of ceramic plates and an electro-mechanical tuner. A fixed-plate prototype of a resonator has been manufactured and tested in an optical laboratory setup devised to excite it with a horn antenna and observe its resonant spectral feature from reflectivity measurements. A detailed description of the setup, the post-processing of the data and the observed resonant structure are treated in this work.

We present the instrument integration and on-sky commissioning results for Kuntur, the LLAMA 690GHz receiver, on loan to the James Clerk Maxwell Telescope (JCMT). The LLAMA 690GHz receiver is a state-of-the-art sideband-separating (2SB), dual polarization receiver, built by the Netherlands Research School for Astronomy (NOVA) laboratory at Groningen, for the Large Latin American Millimeter Array (LLAMA), Argentina. In collaboration with LLAMA, the Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan (ASIAA) and the Greenland Telescope (GLT), the receiver cartridge and WCA have come on loan to JCMT for on-sky commissioning and future VLBI observing tests. The results reveal the potential for single dish observing science at 690GHz with JCMT on Maunakea and provides a pointer to future 690GHz science for both the GLT and LLAMA.

The Probe far-Infrared Mission for Astrophysics (PRIMA) is a proposed space observatory which will use arrays of thousands of kinetic inductance detectors (KIDs) to perform low- and moderate-resolution spectroscopy throughout the far-infrared. The detectors must have noise equivalent powers (NEPs) at or below 1×10⁻¹⁹ W Hz^−1/2 to be subdominant to noise from sky backgrounds and thermal noise from PRIMA’s cryogenically cooled primary mirror. Using a Radio Frequency System on a Chip for multitone readout, we measure the NEPs of detectors on a flight-like array designed to observe at a wavelength of 210 μm. We find that 92% of the KIDs measured have an NEP below 1 × 10⁻¹⁹ W Hz^−1/2 at a noise frequency of 10 Hz.

The North-West University’s Nooitgedacht Observatory has installed four 3.7 m antennas for the purpose of radio interferometry observations in the L and C bands. This paper describes an improve low-noise block downconverter for spectral and continuum measurements, using a single coaxial port for IF transport, local reference distribution, DC biasing and noise injection control. The science cases for this receiver system are: (1) Bright 6.7 GHz methanol (CH3OH) maser monitoring observation (in spectral mode), (2) monitoring observations of bright radio galaxies like quasars, (3) and solar observations. We present details on the design of a signal multiplexing system, injection-locking mechanism, and noise-injection system. The design features an average system temperature of 490K, with an average passband gain of 48.8 dB, and 460 MHz input bandwidth and a calibration noise source with a noise temperature of 20000K.

Not long after the Planck space mission launch, it appeared that the data from the High Frequency Instrument (HFI), based on 100 mK bolometric detectors, was heavily contaminated by cosmic rays. The heat dissipation in the detectors due to these particle hits created spurious signals, appearing as glitches in the data. Further post-launch studies allowed for most of these glitches to be removed. To avoid similar problems in future space or balloon-borne missions, prototype detectors must be tested for particle hit susceptibility to adapt their design for better immunity.

A large cryogenic facility has been developed for this purpose, allowing the irradiation of cryogenic detectors and focal plane components with particles such as protons of various energies with either an internal radioactive source or by connecting it with a particle accelerator. Our facility DRACuLA (Detector irRAdiation Cryogenic faciLity for Astrophysics) has been operated at the ALTO particle accelerator facility during May 2024 to study such effects by irradiating particles with different energy levels on a TES (Transition Edge Sensor). We present the cryogenic performances of this facility during these measurements, with experimental results.

We present a characterization of the mapping from resonant frequency to spatial position for a kilopixel kinetic inductance detector (KID) array developed for the Probe far-Infrared Mission for Astrophysics (PRIMA). This work targets the longest wavelength band of PRIMA’s FIRESS spectrometer, which in total spans 24 to 235 μm. Light emitting diodes arrayed to match repeating unit cells of 16 KIDs first discriminate among unit cells. Within each unit cell, frequencies are widely spaced, so positions are discriminated by theoretical predictions of the relative frequency spacing between detectors based on KID geometries. With this mapping, we analyze board features to improve the accuracy of modeling PRIMA KIDs and inform future fabrication runs.

Prime-Cam, a first-generation science instrument for the Atacama-based Fred Young Submillimeter Telescope, is being built by the CCAT Collaboration to observe at millimeter and submillimeter wavelengths using kinetic inductance detectors (KIDs). Prime-Cam’s 280 GHz instrument module will deploy with two aluminum-based KID arrays and one titanium nitride-based KID array, totaling ∼10,000 detectors at the focal plane, all of which have been fabricated and are currently undergoing testing. One complication of fielding large arrays of KIDs under dynamic loading conditions is tuning the detector tone powers to maximize signal-to-noise while avoiding bifurcation due to the nonlinear kinetic inductance. For aluminum-based KIDs, this is further complicated by additional nonlinear effects which couple tone power to resonator quality factors and resonant frequencies. While both nonequilibrium quasiparticle dynamics and two-level system fluctuations have been shown to give rise to qualitatively similar distortions, modeling these effects alongside nonlinear kinetic inductance is inefficient when fitting thousands of resonators on-sky with existing models. For this reason, it is necessary to have a detailed understanding of the nonlinear effects across relevant detector loading conditions, including how they impact on on-sky noise and how to diagnose the detector’s relative performance. We present a study of the competing nonlinearities seen in Prime-Cam’s 280 GHz aluminum KIDs, with a particular emphasis on the resulting distortions to the resonator line shape and how these impact detector parameter estimation.

SCUBA-2 is a world leading wide field submillimeter camera on the JCMT, producing a wide range of science results, including a unique series of large survey programs. The SCUBA-2 instrument and TES detector arrays have been in constant operation for over a decade at JCMT. The arrays are Transition Edge Sensors fabricated on 3” silicon wafers and read out by a Superconducting Quantum Interference Device (SQUID) multiplexer. Each wafer has an array of 32x40 TES bolometers with the associated SQUID readout. The camera has in total eight TES arrays, four at each wavelength band. With each array having 1,280 bolometers there are in total 5,120 bolometers per wavelength. The instrument is cooled by three pulse tube coolers and a dilution refrigerator. The dilution fridge, with its own pulse tube cooler, has a base temperature of about 50mK. The cryostat itself is very large so that it can accommodate the three large mirrors, located in the 1K optics box, for the field of view of 43 sqarcmins. The other two pulse tube coolers keep the mirrors at temperatures below 10K to minimize the thermal background on the arrays. Mounted within the 1K box are the two focal plane units that contain the cold electronics and the 450μm and 850μm arrays, which are cooled to below 100mK. The still and mixing chamber of the liquid cryogen-free dilution refrigerator cool the 1K box and arrays respectively. The cold shutter is the only moving mechanism within the instrument and is critical for taking dark frames. The shutter is mounted on the outside of the 1K box and provides a uniform background (at roughly 1K) to the arrays. In this paper we review the performance of (a) the NIST fabricated TES wafters and 2D Time Domain SQUID MUX over the past ten years and numerous thermal cycles, (b) the cryogens, which consists of the original liquid cryogen-free dilution fridge and three Cryomech pulse tubes and (c) the cryostat, including the cold shutter.

The goal of the SPID/IQSENS project is the development of SNSPD for specific applications, requiring wavelength sensitivity longer than the communication window of 1550 nm. In this paper, the status of the research and development of SNSPD within the SPID/IQSENS is presented.

Wide-field-of-view millimeter-wave telescopes have been developed for astronomical observations, such as cosmic microwave background (CMB) polarimetry. These telescopes often employee phase-insensitive detectors that are fabricated with the on-chip feed antennas. A holographic field-retrieval method is useful for near-field antenna measurements of such telescopes. Among several variations of the methods, we present the one using the phase shifting of the reference waves, which do not require a fine frequency sweeping. This method aims at application to the ground testing of the LiteBIRD Low-Frequency Telescope (LFT) antenna, which observes the CMB and foreground radiations at 34–161 GHz. In our experiments conducted with a LFT 1/4-scaled antenna, the new method indicated an accuracy of −56 dB levels, which is required for the sidelobe levels of the LFT.

The development of millimeter-wave absorbers for astronomical instruments is an important area of research regarding stray light suppression. Millimeter-wave absorbers for space missions should be selected based not only on their broadband performance at oblique incidence but also on their polarization characteristics, weight, and radiation tolerance. LiteBIRD is a space telescope designed to test inflationary theories by observing the polarization of the cosmic microwave background (CMB). The Low-Frequency Telescope (LFT) on board LiteBIRD needs to know the far side lobes at the −56 dB level, so surrounding it with millimeter-wave absorbers suppresses stray light. Because even the smallest stray light reflection may cause non-negligible far side lobes in the millimeter-wave absorber inside the telescope, it is necessary to accurately measure the reflectance of the millimeter-wave absorber not only specular reflection but also diffuse reflection. We performed near-field reflection measurements of a new lightweight absorber for two polarizations with a 30 degree angle of incidence in the frequency range between 70 GHz and 110 GHz. Measurements showed a reflectance of -16 dB for TE and -19 dB for TM, lower than the industry standard Eccosorb AN-72. In addition, we evaluated radiation tolerance and confirmed that the difference in reflectance before and after exposure was within 3 dB.

Front-end polarization modulation enables improved polarization measurement stability by modulating the targeted signal above the low-frequency 1/f drifts associated with atmospheric and instrumental instabilities and diminishes the impact of instrumental polarization. In this work, we present the design and characterization of a new 60-cm diameter Reflective Half-Wave Plate (RHWP) polarization modulator for the 90 GHz band telescope of the Cosmology Large Angular Scale Surveyor (CLASS) project. The RHWP consists of an array of parallel wires (diameter 50 μm, 175 μm pitch) positioned 0.88 mm from an aluminum mirror. In lab tests, it was confirmed that the wire resonance frequency (fres) profile is consistent with the target, 139 Hz< f_res < 154 Hz in the optically active region (diameter smaller than 150 mm), preventing the wire vibration during operation and reducing the RHWP deformation under the wire tension. The mirror tilt relative to the rotating axis was controlled to be < 15′′, corresponding to an increase in beam width due to beam smearing of < 0.6′′, negligible compared to the beam’s full-width half-maximum of 36′. The median and 16/84th percentile of the wire–mirror separation residual was 0.048^{+0.013 −0.014 mm} in the optically active region, achieving a modulation efficiency ϵ = 96.2^{−0.4 +0.5%} with an estimated bandpass of 34 GHz. The angular velocity of the RHWP was maintained to an accuracy of within 0.005% at the nominal rotation frequency (2.5 Hz). The RHWP has been successfully integrated into the CLASS 90 GHz telescope and started taking data in June 2024, replacing the previous modulator that has been in operation since June 2018.

In this manuscript, a rapid design process flow for multi-layered Terahertz (THz) optical components for Cosmic Microwave Background (CMB) telescopes using artificial dielectric metamaterials made up of periodic 2D grid of metal squares embedded in a dielectric material with a fixed interlayer spacing, termed ”capacitive grids”, is discussed. The modeling of such metamaterials using ideal RF transmission line sections to achieve an arbitrary value of refractive index and their fabrication using aluminum embedded in a polyimide dielectric is presented. Finally, the design and HFSS simulations results of a stepped-impedance low-pass quasi-optic metamaterial filter is discussed as an application of such a rapid design methodology in designing complex quasi-optical components with variable refractive indices in the millimeter wave and THz astronomy applications.

Simultaneous dual polarization observations at multiple frequencies are crucial for understanding time-varying astronomical phenomena. To achieve this, it is necessary to separate the main radio telescope beam into different frequency components to feed various receivers. This paper presents our innovative optical diplexer design, based on the layering of dielectric materials. By stacking nine periodic layers of low-loss High Resistivity Silicon (HR-Si) and Low-Density Polyethylene (LDPE), we have developed a diplexer that separates frequency bands centered around 220 GHz and 350 GHz. This diplexer design has applications in the wideband Submillimeter Array (wSMA). Future optical diplexer designs utilizing dielectric stacks will enable dual polarization multi-band observations with the next generation Event Horizon Telescope (ngEHT) and the Black Hole Explorer (BHEX).

Due to high dynamic range and ease of use, continuous wave terahertz spectroscopy is an increasingly popular method for optical characterization of components used in cosmic microwave background (CMB) experiments. In this work, we describe an optical testbed that enables simultaneous measurements of transmission and reflection properties of various radiation absorbing dielectric materials, essential components in the reduction of undesired optical loading. To demonstrate the performance of the testbed, we have measured the reflection response of five absorbers commonly used for such applications: TKRAM, carbon- and iron-loaded Stycast, HR10, AN72, and an in-house 3D printed absorber across a frequency range of 100 to 500 GHz, for both S- and P-polarization, with incident angles varying from 15° to 45°. We present results on both the specular and scattered reflection response of these absorbers.

LiteBIRD is an JAXA-led strategic L-class satellite mission designed to measure the primordial B modes of the cosmic microwave background radiation (CMB) to test cosmic inflation. The LiteBIRD Low-Frequency telescope employs a polarization modulator unit (PMU). The PMU is placed at the telescope aperture to modulate the incoming CMB polarization signal by using a continuous rotating half-wave plate to reduce the impact of 1/f noise and differential systematic effects. The current PMU design employs three cryogenic holder mechanisms that hold the rotor until the superconducting magnet bearing cools below its critical temperature after launch. They also serve a conductive path to the rotor when they are held. Minimizing the heat dissipation of this holder is one of the key development goals of the PMU due to the limited cooling power on the satellite system. In this paper, We report on the detailed design of the holder and the developed cryogenic stepping motor that actuates the holder. Also, we conducted the preliminary thermal characterization at around 7 K. The preliminary estimated total heat dissipation of the holder is 2.39 ± 0.09 mW when we activated it for 532 s.

Many experimental efforts are striving to provide deep maps of the cosmic microwave background (CMB) to shed light on key questions in modern cosmology. The primary science goal for some of these experiments is to further constrain the energy scale of cosmic inflation. It has been shown that these experiments are particularly sensitive to optical systematics. Near-field vector beam mapping, or holography, is now employed in a variety of CMB-focused experimental efforts due to the technique’s ability to provide full details of electromagnetic field propagation through complex systems. In this proceeding, we describe the development of a measurement bench for millimeter-wave phase-sensitive beam mapping with the goal of characterizing optical components for CMB experiments. We discuss the testing of a beam scanner based on a 6-axis robot arm, the related custom control software, the readout architecture, and the overall validation of the system through various testing procedures. Dynamic range of 70 dB is demonstrated for the presented setup. With the current mechanical setup, we derive an upper limits of 45 μm on the absolute positioning error and 10 μm on positional repeatability.

We present designs and fabrications of sub-wavelength anti-reflection structures on alumina for infrared filters at three observational frequency bands near 30, 125, and 250 GHz, which are widely used for instruments measuring cosmic microwave background (CMB) radiation from the ground. The three observational windows contain the two observational bands in each receiver, and the corresponding fractional bandwidth is about 60%. We used laser ablation to directly machine on alumina substrate. This technology is robust against the use of an optical element at the cryogenic temperature with which all the CMB telescope receivers have to comply. Based on the fabricated 9 (3 × 3) pyramidal structures, we computed the expected averaged transmittance of above 0.97 for each of the three filter designs including anticipated absorptive loss, the loss tangent of 4 × 10₋₄, and the incident angle up to 20 degrees. The band averaged instrumental polarization, the fractional difference between the p and s-state incident polarization states, is computed and they are less than ±4 × 10₋₃ for the bands and incident angles.

The LiteBIRD mission is a next generation CMB space mission which aims at detecting CMB polarization produced by primordial gravitational waves, with a sensitivity for the tensor to scalar ratio δr < 0.001. A polarization modulator unit (PMU) represents a critical and powerful component to avoid 1/f noise contributions and mitigate differential systematic uncertainties in orthogonal polarization sensitive detectors on both Mid- and High- Frequency Telescopes.

Each PMU is based on a continuously transmissive rotating half-wave plate (HWP), held by a superconducting magnetic bearing operating in the 5K environment. The dynamical behaviour of the system during the rotation must be monitored, since it can introduce systematic effects during the measurements. In this contribution, we present the development of custom cryogenic capacitive sensors, used to monitor the spinning rotor. A set of these sensors allows to monitor the levitation height and wobbling of the rotor, with accuracy of ~ 5 μm and ~ 0.1′, respectively. A thermistor mounted on the rotor can be coupled with one of these capacitors, so that it can be properly biased and read.

COSMO (COSmic Monopole Observer) is an experiment aimed at the searching for spectral distortions in the CMB (Cosmic Microwave Background) between 120 and 300 GHz. COSMO will be operated from Concordia Station on the Antarctic plateau. The experiment is based on a cryogenic Martin-Puplett interferometer whose superconductive detectors are KIDs (Kinetic Inductance Detectors). The interferometer produces interferograms proportional to the difference between the sky and an internal reference black body. The sky signal has a fast modulation to compensate for the atmospheric fluctuations. A key requirement of the readout is an ultra-fast rate to track the signal modulation and also for detector diagnostic. The readout architecture is based on an IQ transceiver generating a comb of test tones tuned to each detector. We developed a modular readout based on commercial components for reliability and fast prototyping. We were able to reach and sustain a readout rate higher than 60 kHz for 18 detectors. In this contribution a general description of the architecture, together with the main performances in terms of amplitude and phase noise are given.

Prime-Cam is a first-generation science instrument for the CCAT Observatory’s six-meter aperture Fred Young Submillimeter Telescope (FYST). FYST’s crossed-Dragone design provides high optical throughput to take advantage of its unique site at 5600 m on Cerro Chajnantor in Chile’s Atacama Desert to reach mapping speeds over ten times greater than current and near-term submillimeter experiments. Housing up to seven independent instrument modules in its 1.8-meter diameter cryostat, Prime-Cam will combine broadband polarization-sensitive modules and spectrometer modules designed for observations in several frequency windows between 210 GHz and 850 GHz to study a wide range of astrophysical questions from Big Bang cosmology to the formation of stars and galaxies in the Epoch of Reionization and beyond. In order to cover this range of frequencies and observation modes, each of the modules contains a set of cold reimaging optics that is optimized for the science goals of that module. These optical setups include several filters, three or four anti-reflection-coated silicon lenses, and a Lyot stop to control the field of view and illumination of the primary mirror, satisfy a series of mechanical constraints, and maximize optical performance within each passband. We summarize the design considerations and trade-offs for the optics in these modules and provide a status update on the fabrication of the Prime-Cam receiver and the design of its 1 K and 100 mK thermal BUSs.

The Simons Observatory is a new ground-based cosmic microwave background experiment, which is currently being commissioned in Chile’s Atacama Desert. During its survey, the observatory’s small aperture telescopes will map 10% of the sky in bands centered at frequencies ranging from 27 to 280 GHz to constrain cosmic inflation models, and its large aperture telescope will map 40% of the sky in the same bands to constrain cosmological parameters and use weak lensing to study large-scale structure. To achieve these science goals, the Simons Observatory is deploying these telescopes’ receivers with 60,000 state-of-the-art superconducting transition-edge sensor bolometers for its first five year survey. Reading out this unprecedented number of cryogenic sensors, however, required the development of a novel readout system. The SMuRF electronics were developed to enable high-density readout of superconducting sensors using cryogenic microwave SQUID multiplexing technology. The commissioning of the SMuRF systems at the Simons Observatory is the largest deployment to date of microwave multiplexing technology for transition-edge sensors. In this paper, we show that a significant fraction of the systems deployed so far to the Simons Observatory’s large aperture telescope meet baseline specifications for detector yield and readout noise in this early phase of commissioning.

Cosmic Microwave Background experiments need to measure polarization properties of the incoming radiation very accurately to achieve their scientific goals. As a result of that, it is necessary to properly characterize these instruments. However, there are not natural sources that can be used for this purpose. For this reason, we developed the PROTOtype CALibrator for Cosmology, PROTOCALC, which is a calibrator source designed for the 90 GHz band of these telescopes. This source is purely polarized and the direction of the polarization vector is known with an accuracy better than 0.1°. This source flew for the first time in May 2022 showing promising result.

In this paper we present the European Low Frequency Survey (ELFS), a project that will enable foregrounds-free measurements of the primordial B-mode polarization and a detection of the tensor-to-scalar ratio, r, to a level σ(r) = 0:001 by measuring the Galactic and extra-galactic emissions in the 5–120 GHz frequency window. Indeed, the main difficulty in measuring the B-mode polarization comes from the fact that many other processes in the Universe also emit polarized microwaves, which obscure the faint Cosmic Microwave Background (CMB) signal. The first stage of this project is being carried out in synergy with the Simons Array (SA) collaboration, installing a 5.5–11GHz (X-band) coherent receiver at the focus of one of the three 3.5m SA telescopes in Atacama, Chile, followed by the installation of the QUIJOTE-MFI2 in the 10–20 GHz range. We designate this initial iteration of the ELFS program as ELFS-SA. The receivers are equipped with a fully digital back-end that will provide a frequency resolution of 1MHz across the band, allowing us to clean the scientific signal from unwanted radio frequency interference, particularly from low-Earth orbit satellite mega constellations. This paper reviews the scientific motivation for ELFS and its instrumental characteristics, and provides an update on the development of ELFS-SA.

Atmospheric interference, noise, and attenuation are a few limitations that arise when observing emissions of sub-millimeter wavelengths using ground-based telescopes. On-going research conducted on high-altitude balloons allow a new direction in observing these distributed emissions and eliminates all possible atmospheric interference. All sub-millimeter balloons and ground-based telescopes could benefit from a compact, re-configurable, high gain, programmable amplifier module to use in their receivers. We have designed, built, and tested an amplifier module for the Astrophysics Stratospheric Telescope for High Spectral Resolution Observations at Sub-millimeter wavelengths (ASTHROS), which is a high-altitude balloon mission that utilizes high-spectral resolution spectrometry to analyze stellar feedback by mapping ionized gas from the Milky Way galaxy and other neighboring galaxies. Using a five-stage Intermediate Frequency (IF) Low Noise Amplifier (LNA) added to a readout chain using commercial off-the-shelf components, the amplifier module yields 74 dB of gain up to 3.5 GHz with 31.75 dB of programmable attenuation with relatively linear gain flatness of ±1 dB, all while consuming 2.25 W per module (9 V at 250 mA).

While the amplification techniques and technology in this field are not new, achieving such high gain in systems usually require a significant amount of space to be allocated onboard. To alleviate this issue, this amplifier module has a unique form factor that combines the entire amplifier chain and bias system all in one module, saving space and weight on the system. The form factor design also allows the module to be stacked on top of one another to provide a higher range of gain in the system. Currently, the modules can be stacked up to eight times, and can be connected to allow for full control of the system with the use of a microcontroller. Sub-millimeter systems can have a set of 8 modules, all while saving space and reducing used weight.

We describe a two-stage cryogenic low noise amplifier (LNA) with a usable frequency range of 0.5 to 8 GHz (L to C-band) designed for operation at 4 Kelvin. The amplifier was designed to have high linearity and dynamic range with a low noise temperature and low power dissipation. The LNA uses two Diramics Indium Phosphide (InP) Pseudomorphic High Electron Mobility Transistors (pHEMTs) and other commercial surface mount (SMT) components. The use of SMT components minimizes the number of bond wires needed to assemble the amplifier increasing its manufacturability. The LNA has a gain of 25 dB with a gain flatness of ±1 - 2 dB and a power consumption at 4 Kelvin ranging from 3.4 to 8 mW. The measured noise temperature at an operating temperature of 10 Kelvin is less than 10 Kelvin from 1 GHz to 2 GHz, less than 8 Kelvin from 2 GHz to 4 GHz, less than 6 Kelvin from 4 GHz to 5 GHz and less than 4 Kelvin from 5 GHz to 9.5 GHz. The measured performance is in good agreement with the computer simulation with a output 1 dB compression point (OP1dB) ~-5 dBm and input third order intercept point (IIP3) ∼ -12 dBm when measured with a full readout chain. The amplifier is designed to be used as the first stage LNA in the readout of arrays of microwave multiplexed transition edge sensors (TES) for the Simons Observatory¹ (SO) in Chile. A common problem with highly sensitive frequency multiplexed detectors is optimizing the probe-tone drive power without saturating the LNA. The high dynamic range of these LNAs sets a saturation point well above the saturation point of the detectors.

In pursuit of advancing large array receiver capabilities and enhancing the 16-element Heterodyne Array Receiver Program (HARP) instrument on the James Clerk Maxwell Telescope (JCMT), we have successfully fabricated 230 GHz finline superconductor-insulator-superconductor (SIS) mixers. These mixers are critical for assessing the potential and prospective for the HARP instrument’s upgrade. Unlike the existing HARP’s mixer, we replace the probe antenna with an end-fire unilateral finline as the waveguide to planar circuit transition. This mixer design is expected to operate from about 160–260 GHz (approximately 47% bandwidth), and the mixer chips’ current-voltage (I-V) curves have been characterized, showing promising results with a quality factor (R_sg/R_n) exceeding 9.3. Evaluation of the double-sideband (DSB) receiver noise temperature (T_rx) is currently underway. Once successfully characterised, our immediate aim is to scale the mixer to operate at HARP’s frequency range near 345 GHz to achieve similar broad RF bandwidth performance. Ongoing simulations are currently being conducted for the design of the 345 GHz finline mixer. This work marks a crucial step toward enhancing HARP receiver performance with better sensitivity and wider Intermediate Frequency (IF) bandwidth, enabling higher-frequency observations, and expanding the scientific potential of the JCMT and its collaborative partners.

VLBI Exploration of Radio Astrometry (VERA) is a VLBI facility operated by the National Astronomical Observatory of Japan. It comprises four 20 m radio telescopes located across the country. VLBI observations at 86 GHz allow us to explore the jet base of nearby active galactic nuclei. In recent years, the development of the 86 GHz receiver systems at the East Asia VLBI Network (EAVN) has started. Currently, only three Korea VLBI Network (KVN) antennas provide 86 GHz VLBI capability in the member stations of EAVN. The participation of VERA in the 86 GHz VLBI observations will boost resolution, sensitivity, and dynamic range. Therefore, we are developing a new 86 GHz low noise receiver system to be installed at VERA Mizusawa and Ishigaki stations. We are considering a cooled circular polarization receiver covering a wide frequency range of 67−116 GHz with the capability of cooling HEMT amplifiers. We are developing a room temperature 2 side band (2SB) system for down-converting signals in the 67−116 GHz band. Recently developed room-temperature mixers with an IF frequency over 25 GHz could cover most of the 67−116 GHz RF signals in a single observation. In this poster, we will discuss the development progress of the 2SB receiver and the design status of the cooling Dewar.

The Millimetron Space Observatory will be equipped with the cryogenically cooled instrument for a Space-Earth Very Large Baseline Interferometry (S-E VLBI). It will be a multi-channel heterodyne receiver with 7mm, 3mm, 1.3mm and 0.8mm channels. The VLBI instrument will have a multi-frequency capability, provided by signal splitting in the input optics and by back-end functionalities. The optical design is shown in this report.

The well-established technology of the superconducting quantum parametric amplifier (SPA) can be reconfigured to perform functions beyond amplification, such as frequency multiplication, by utilising the low-noise, low-loss superconducting nonlinear transmission line. This versatile technology holds potential for various applications, including ‘pumping’ a millimetre (mm) or sub-mm wave heterodyne mixer or driving a high-frequency SPA. Its significance lies in the ability to incorporate a high-purity signal source into the cryogenic stage alongside the primary detector, thereby eliminating noise associated with room temperature sources. Additionally, there is potential for on-chip integration with the detector circuit, leading to a more compact architecture.

This manuscript details the design of a travelling-wave parametric multiplier (TWPaM) that exploits the nonlinear wave-mixing mechanism to enhance the third harmonic growth from a strong pump tone injected into the travelling wave parametric amplifier (TWPA)-like device. While this functionality has been demonstrated previously, it exhibited narrowband performance. In this manuscript, we present our approach to designing a dispersion engineering scheme that enables the generation of broadband tunable tripler tones with high conversion efficiency. We showcase our design methodology using a niobium titanium nitride (NbTiN) high-gap thin-film transmission line as an example. Our presentation includes the theoretical model governing the physics of higher harmonics generation, emphasising phase-matching conditions that allow for broadband operation while suppressing unwanted modes. Although the ultimate aim is to develop a mm/sub-mm TWPaM, we aim to demonstrate the feasibility of their operation with a scaled microwave design in this manuscript. We will show that we can theoretically achieve close to 35% conversion efficiency across approximately 60% operational bandwidth.

The Atacama Large Millimeter/submillimeter Array (ALMA) is the largest (sub)mm-wavelength ground-based telescope and has been producing ground-breaking science since it became operational in 2011. The ALMA Development Roadmap was released in 2018 to prioritize the developments necessary to significantly expand ALMA’s capabilities and enhance its scientific reach in the coming decades. The ALMA2030 Wideband Sensitivity Upgrade (WSU) is the top priority initiative for the Development Roadmap. The WSU will initially double, and eventually quadruple, ALMA’s system instantaneous bandwidth and deliver improved sensitivity by upgrading the receivers, digital electronics, and correlator. The WSU will afford significant improvements for every future ALMA observation, whether it is focused on continuum or spectral line science. The improved sensitivity and spectral tuning grasp will open exciting new avenues of science capability, increase sample sizes, and enable more efficient observations.

The WSU is now well underway with key subsystems under development, including new receivers, digitizers, data transmission system and correlator. In parallel, the observatory is advancing the detailed planning towards implementation through a careful project management and systems engineering approach, based on an integrated Conceptual System Design which outlines the hardware, computing and science operations aspects of the upgrade. The substantial gains in the observing efficiency enabled by the WSU will further enhance ALMA as the world leading facility for millimeter/submillimeter astronomy.

The IAC Electronics Department has developed a high-performance embedded Data Acquisition System (eDAS) to perform the readout of an array of microwave kinetic inductance detectors (MKIDs) and to carry out hardware-based digital signal processing in real time. The eDAS has been developed using the Zynq UltraScale+ RFSoC ZCU111 Evaluation Kit and PYNQ software framework. The ultimate goal is to be able to detect changes in the amplitude and phase of the MKID’s signal when a photon arrives at the detector, in order to observe a single photon signature. We have been able to identify the resonant frequency of individual pixels in total darkness.

The Fred Young Submillimeter Telescope (FYST), on Cerro Chajnantor in the Atacama desert of Chile, will conduct wide-field and small deep-field surveys of the sky with more than 100,000 detectors on the Prime-Cam instrument. Kinetic inductance detectors (KIDs) were chosen as the primary sensor technology for their high density focal plane packing. Additionally, they benefit from low cost, ease of fabrication, and simplified cryogenic readout, which are all beneficial for successful deployment at scale. The cryogenic multiplexing complexity is pulled out of the cryostat and is instead pushed into the digital signal processing of the room temperature electronics. Using the Xilinx Radio Frequency System on a Chip (RFSoC), a highly multiplexed KID readout was developed for the first light Prime-Cam and commissioning Mod-Cam instruments. We report on the performance of the RFSoC-based readout with multiple detector arrays in various cryogenic setups. Specifically we demonstrate detector noise limited performance of the RFSoC-based readout under the expected optical loading conditions.

CMB-S4 is the next generation, ground-based, cosmic microwave background (CMB) observatory. It is designed to explore the scientific potential contained in the CMB temperature and polarization anisotropies. The goal of CMB-S4 is to observe the mm sky with about 500,000 transition edge sensors (TES). These cryogenic detectors are read out using time division multiplexing (TDM). Two stages of superconducting quantum interference devices (SQUIDs) are used at cryogenic temperatures for multiplexing and amplifying the signals coming from the TESs. This imposes stringent noise requirements to the electronics for readout. In this paper, we discuss the developments and the first tests of an analog front-end differential electronics daughter board. The board is based on an SiGe application-specific integrated circuit (ASIC), the AwaXe v3, developed for the readout of ATHENA’s X-IFU instrument. It provides low-noise amplification (LNA) after the cryogenic multiplexer and supplies the low noise current biasing for the two SQUID stages and TESs. This front-end electronics is expected to improve the noise performances of the CMB-S4 readout chain and help moving towards a differential and compact design.

We summarize the technical specifications of TIME, the Tomographic Ionized-carbon Mapping Experiment, which is designed to probe the structure and evolution of the universe by using line intensity mapping to measure carbon monoxide (CO) and ionized carbon ([C ii]) with a mm-wavelength grating spectrometer. We present detector count, spectral coverage and resolution, and give an update on the current status of the project. TIME was installed at the Arizona Radio Observatory 12 m telescope in 2019 and returned for further engineering, commissioning, and observing in 2022. Data taken during the 2022 season demonstrate the ability of TIME to compensate for field rotation through the use of a K-mirror system, as well as spectro-imaging functionality broadly in line with expectations given the current state of the instrument. TIME will return to ARO for science observations for the Winter 2024 season. We discuss hardware and software updates and preliminary data analysis in preparation for science scans.

The Epoch of Reionization Spectrometer (EoR-Spec) is an instrument module with unique spectroscopic capabilities within the Prime-Cam receiver on the Fred Young Submillimeter Telescope (FYST), a forthcoming six-meter aperture telescope to be situated on Cerro Chajnantor in the Atacama Desert, Chile. Engineered to investigate the processes of reionization and galaxy formation in the early universe, EoR-Spec employs line intensity mapping techniques to measure the [CII] fine-structure lines for the redshift range spanning from z=3.5 to 8. The module integrates a cryogenic scanning Fabry-Perot interferometer (FPI) to meet the spectral resolution criterion of approximately R=100. At the core of the FPI lie two parallel, identical highly reflective silicon-based mirrors, with a 14 cm aperture that form a resonating cavity, referred to as an etalon. These mirrors feature double-layer metamaterial anti-reflection coatings (ARC) on one side, complemented by metal mesh reflectors on the other. The double-layer ARC ensures minimal reflectance on the substrate surface and facilitates tailoring of the reflectance profile across the FPI bandwidth. The characterization of silicon mirrors and prototype testing are crucial steps in ensuring the optimal performance and functionality of the EoR-Spec instrument. Here we present an updated account of the ongoing efforts involved in the characterization of silicon mirrors and the mounting test conducted for the EoR-Spec instrument.

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne telescope designed to survey star formation over cosmological time scales using intensity mapping in the 420 – 540 GHz frequency range. EXCLAIM uses a fully cryogenic telescope coupled to six on-chip spectrometers featuring kinetic inductance detectors (KIDs) to achieve high sensitivity, allowing for fast integration in dark atmospheric windows. The telescope receiver is cooled to ≈ 1.7 K by immersion in a superfluid helium bath and enclosed in a superfluid-tight shell with a meta-material anti-reflection coated silicon window. In addition to the optics and the spectrometer package, the receiver contains the magnetic shielding, the cryogenic segment of the spectrometer readout, and the sub-Kelvin cooling system. A three-stage continuous adiabatic demagnetization refrigerator (CADR) keeps the detectors at 100 mK while a 4He sorption cooler provides a 900 mK thermal intercept for mechanical suspensions and coaxial cables. We present the design of the EXCLAIM receiver and report on the flight-like testing of major receiver components, including the superfluid-tight receiver window and the sub-Kelvin coolers.

SKARAB is the acronym for Square Kilometer Array Reconfigurable Application Board, a digital platform that was initially designed for the MeerKAT digital correlator. Being equipped with a reprogrammable chip like a Virtex7 FPGA, SKARAB is a not application-specific computing node 19’’ 1U dimension, thus suitable to be employed for single-dish applications as well. Here we present a SKARAB pulsar machine that has been engineered and built for the Sardinia Radio Telescope (SRT, Italy). The high dynamic range provided by the high-performing ADC mezzanine card (which provides digital samples coded with up to 16 bits) coupled with the SKARAB guarantees a proper functionality also in presence of strong Radio Frequency Interference (RFI), and the 4x40G I/O mezzanine card allows handling data rates up to 160 Gbit/sec.

Both pulsar search and pulsar timing are provided in different bandwidths and number of channels; we also present on-field results that we have achieved at the Sardinia Radio Telescope by observing the pulsar B0355+54 at 5 GHz.

The Lunar Surface Electromagnetics Experiment - Night, LuSEE-Night, is a low-frequency radio astronomy experiment that will explore the cosmic Dark Ages signal on the radio-quiet far side of the Moon. The LuSEE-Night carries a radio frequency spectrometer consisting of a set of antennas, analog and digital processing electronics, and will be launched by NASA’s Commercial Lunar Payload Services in 2025. The spectrometer is designed to observe the spectrum of the radio sky in the 0.5−50MHz band. The flight model (FM) of the four-channel spectrometer has been developed. The FM has been characterized for linearity, gain, noise, and their temperature dependence, confirming that the FM meets all the requirements for LuSEE-Night.

We have been developing a wideband heterodyne receiver for simultaneous observations in isotopologue CO lines of J = 2–1 and J = 3–2 transitions with dual-polarization. To achieve these simultaneous observations, a wideband frequency separation system was required in the radio frequency circuit because the intermediate frequency range of the superconductor-insulator-superconductor mixer is narrower than the frequency range of the CO lines from J = 2–1 to J = 3–2. As the frequency separation system, a waveguide multiplexer that connects three types of diplexers was applied. The prototype multiplexer was already developed and installed in the 1.85-m radio telescope. Then, we succeeded in commissioning observations simultaneously in 230 and 345 GHz bands with single polarization. We are currently working on improving the multiplexer and developing a 90° differential phase shifter and a wideband orthomode transducer (OMT). The 90° differential phase shifter and OMT can be combined to operate as a circular polarizer. We are planning to realize observations of both linearly and circularly polarized waves by using the OMT and circular polarizer, respectively. A part of this development can contribute to the future development of Atacama Large millimeter/submillimeter Array and Very Long Baseline Interferometry telescopes. In this paper, we describe the development of the prototype wideband receiver and the development status of the OMT, circular polarizer, and a new multiplexer.

Future millimeter wavelength experiments aim to both increase aperture diameters and broaden bandwidths to increase the sensitivity of the receivers. These changes produce a challenging anti-reflection (AR) design problem for refracting and transmissive optics. The higher frequency plastic optics require consistently thin polymer coats across a wide area, while wider bandwidths require multilayer designs. We present multilayer AR coats for plastic optics of the high frequency BICEP Array receiver (200-300 GHz) utilizing an expanded polytetrafluoroethylene (ePTFE) membrane, layered and compressively heat-bonded to itself. This process allows for a range of densities (from 0.3g/cc to 1g/cc) and thicknesses (>0.05mm) over a wide radius (33cm), opening the parameter space of potential AR coats in interesting directions. The layered ePTFE membrane has been combined with other polymer layers to produce band average reflections between 0.2% and 0.6% on high density polyethylene and a thin high modulus polyethylene window, respectively.

We present transmission and loss measurements of 3D printed alumina and reflectance measurement of a sample with 3D printed sub-wavelength structures anti-reflection coatings (SWS-ARC). For a band between 160 and 700 GHz we find an index of refraction n = 3.11 ± 0.01 and loss tan δ = 0.002 ± 0.003. Transmission measurements between 160 and 250 GHz of a sample with SWS-ARC 3D printed on one side give a reduction of reflectance from a maximum of 64% to a maximum of 31% over the band, closely matching predictions. These first measurements of the index and loss over this frequency band suggest that the material could be useful for astrophysical applications.

Current and future experiments observing the cosmic microwave background require a detailed understanding of optical performance at cryogenic temperatures. Pre-deployment analysis of optics can be performed in custom-engineered cryogenic test beds, such as Mod-Cam, a first light camera for the CCAT project. This work presents studies of the mechanical and thermal performance of CryoSim, a model of a generic cylindrical 4-K cryostat cooled with a commercial pulse tube cryocooler that can be used to characterise optical components and full reimaging optical systems. CryoSim is extensively parametrised, allowing the joint analysis and optimisation of mechanical and thermal performance via finite element methods. Results from this model are validated against measured cooldown data of the Mod-Cam cryostat. Due to the extensive parametrisation of the model, significant modifications of the cryostat geometry may be implemented to be representative of any system the scientific community may desire, and validation of thermal and mechanical performance can be carried out rapidly.

The search for the polarized imprint of primordial gravitational waves in the cosmic microwave background (CMB) as direct evidence of cosmic inflation requires exquisite sensitivity and control over systematics. The next-generation CMB-S4 project intends to improve upon current-generation experiments by deploying a significantly greater number of highly-sensitive detectors, combined with refined instrument components based on designs from field-proven instruments. The Precursor Small Aperture Telescope (PreSAT) is envisioned as an early step to this next generation, which will test prototype CMB-S4 components and technologies within an existing Bicep Array receiver, with the aim of enabling full-stack laboratory testing and early risk retirement, along with direct correlation of laboratory component-level performance measurements with deployed system performance. The instrument will utilize new 95/155 GHz dichroic dual-linear-polarization prototype detectors developed for CMB-S4, cooled to 100mK via the installation of an adiabatic demagnetization refrigerator, along with a prototype readout chain and prototype optics manufactured with wide-band anti-reflection coatings. The experience gained by integrating, deploying, and calibrating PreSAT will also help inform planning for CMB-S4 small aperture telescope commissioning, calibration, and operations well in advance of the fabrication of CMB-S4 production hardware.

The Simons Observatory (SO) is a group of modern telescopes dedicated to observing the polarized cosmic microwave background (CMB), transients, and more. The Observatory consists of four telescopes and instruments, with over 60,000 superconducting detectors in total, located at ∼5,200m altitude in the Atacama Desert of Chile. During observations, it is important to ensure the detectors, telescope platforms, calibration and receiver hardware, and site hardware are within operational bounds. To facilitate rapid response when problems arise with any part of the system, it is essential that alerts are generated and distributed to appropriate personnel if components exceed these bounds. Similarly, alerts are generated if the quality of the data has become degraded. In this paper, we describe the SO alarm system we developed within the larger Observatory Control System (OCS) framework, including the data sources, alert architecture, and implementation. We also present results from deploying the alarm system during the commissioning of the SO telescopes and receivers.

LiteBIRD, a forthcoming satellite mission, aims to measure the polarization of the Cosmic Microwave Background (CMB) across the entire sky. The experiment will employ three telescopes, Transition-Edge Sensor (TES) bolometers and rotating Half-Wave Plates (HWPs) at cryogenic temperatures to ensure high sensitivity and systematic effects mitigation. This study is focused on the Mid- and High-Frequency Telescopes (MHFT), which will use rotating metal mesh HWPs. We investigate how power variations due to HWP differential emissivity and transmittance combine with TES nonlinear responsivity, resulting in an effective instrumental polarization. We present the results of simulations for the current HWP design, modeling the TES deviation from linearity as a second-order response. We quantify the level of acceptable residual nonlinearity assuming the mission requirement on the tensor-to-scalar ratio, δr < 0.001. Moreover, we provide an accuracy requirement on the measurement of TES responsivity nonlinearity level for MHFT channels. Lastly, we present possible mitigation methods that will be developed in future studies.

The Simons Observatory (SO) is a cosmic microwave background experiment composed of three 0.42 m Small Aperture Telescopes (SATs) and one 6 m Large Aperture Telescope (LAT) in the Atacama Desert of Chile. The Large Aperture Telescope Receiver (LATR) was integrated into the LAT in August 2023; however, because mirrors were not yet installed, the LATR optical chain was capped at the 4K stage. In this dark configuration we are able to characterize many elements of the instrument without contributions from atmospheric noise. Here we show this noise is below the required upper limit and its features are well described with a simple noise model. Maps produced using this noise model have properties that are in good agreement with the white noise levels of our dark data. Additionally, we show that our nominal scan strategy has a minimal effect on the noise when compared to the noise when the telescope is stationary.

A new facility instrument open to the scientific community is MISTRAL. The MIllimeter Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs (MISTRAL) is a millimetric multi–pixel camera, mounted at the Gregorian focus of the Sardinia Radio Telescope (SRT), working in the W-band that will be able to study many scientific cases, from the ‘missing baryons’ problem to extragalactic astrophysics, morphology of galaxy cluster and the search of the Cosmic Web through high angular resolution measurements of the Sunyaev-Zel’dovich effect. We present the current state of the map-making and data filtering software that we plan to use for future observations. This software aims to analyze the simulated observations of a target, filter the data from instrumental noise and produce a map, employing a customized common mode removal.

LiteBIRD is a JAXA strategic L-Class mission designed to search for the existence of primordial gravitational waves produced during the inflationary phase of the Universe. This is achieved through measurements of their imprint on the polarization of the cosmic microwave background (CMB). To fulfill the scientific objectives, observations have to be made over a wide range of frequencies (34 GHz - 448 GHz), which is accomplished by three telescopes: the Low-Frequency Telescope (LFT) led by JAXA and the Middle & High-Frequency Telescopes (MHFT) under European responsibility and led by CNES. To withstand the launch, comply with satellite requirements, and minimize the mass of the mechanical structure, we conducted finite element modeling of the entire MHFT, incorporating both modal and quasi-static load analyses. A nodal thermal study was carried out to evaluate, on the one hand, the static thermal loads of the instruments, and on the other hand the sensitivity of the instruments to sinusoidal disturbances simulating those caused by the ADR cooling system. This paper outlines the methodology employed in designing the mechanical structure of the MHFT, then summarizes the initial results and conclusions drawn from various mechanical and thermal analyses performed on the MHFT.

As for any CMB instrument, the accurate knowledge of the beam shape is crucial in order to limit the signal contamination and to have a precise CMB power spectrum reconstruction from the data. The MHFT on the future JAXA-led LiteBIRD space mission, based on a refractive design, will have a wide frequency coverage ranging from 89 to 448 GHz. In order to validate the modeling tools and the level of accuracy achievable on the experimental RF characterisation prior to any complete prototype, a simpler breadboard has been developed for W-Band (75-110 GHz). We present here both the modeling and the RF characterisation results of this breadboard which consists of a dielectric lens that is fed by a corrugated horn. The measurements were performed in the Near-Field, the Far-Field being then obtained through a transformation.

LiteBIRD is a future satellite mission designed to polarization-sensitive mapping of the Cosmic Microwave Background (CMB) anisotropies required to test the theory of cosmological inflation. The standard procedure of the on-ground characterization and calibration of the LiteBIRD Med- and High Frequency Telescopes (MHFT) requires the use a cryogenic reference unit, called also ‘SKYLOAD’, compatible with the vacuum environment.

In this paper, we present one possible baseline design of such SKYLOAD, proposed and currently under development by our research group. The SKYLOAD is composed from anechoic panels, which consist of a planar impedance substrate and a structured layer involving an anechoic cone array with a honeycomb arrangement. Both structured layer and planar impedance substrates should be made of a microwave absorbing polymer, compatible with vacuum cryogenic environment. The SKYLOAD is cooled down by liquid helium to 2 K. Accordingly, in our work, we address also key issues related to no-thermal cracking conditions, as well as the deterioration of the performance of the SKYLOAD assembled from anechoic panels due to their thermal shrinkage when cooling to cryogenic temperatures. Finally, an original manufacturing method of the proposed anechoic panels, involving polymer casting, is currently under consideration.

Antenna-coupled microwave kinetic inductance detectors are emerging as a compelling solution for the next generation of cosmic microwave background (CMB) experiments, which require focal plane arrays with a substantial increase in the number of detectors and multi-band observation capabilities. We present the design and fabrication of multichroic pixels using this architecture, optimized for B-mode polarization observation. The pixel incorporates an improved dual bowtie slot antenna placed at the second focus of an elliptical lens, covering an octave frequency range from 100 GHz to 300 GHz. We aim to achieve bandwidths exceeding 20% for two CMB-atmospheric transparent subbands at 150 GHz and 220 GHz while maintaining adequate linear polarization sensitivity with a cross-polarization level below −17 dB across the entire range. The captured signal is then passed through a superconducting microstrip low-pass filter to remove excessive colors before being fed into the diplexer, where the two bands are separated. These bands are then coupled to the inductive section of MKIDs, effectively modifying the resonant frequency and quality factor of the corresponding resonators. The demonstration sample is fabricated using five photomask layers, employing niobium and aluminum as the superconducting materials, and is currently undergoing testing.