The Large Scale Polarisation Explorer (LSPE) is a balloon-borne experiment aiming to measure the B-mode component
of the CMB polarisation at large angular scales. Onboard LSPE, the Short Wavelength Instrument for the Polarisation
Explorer (SWIPE) is a bolometric polarimeter observing in three bands centred at 140, 220 and 240 GHz. The telescope
is a single large-diameter plano-convex lens with a cold aperture stop. A small number of multi-mode feed horns feeding
bolometric detectors are used within the focal plane, achieving a sensitivity equivalent to that of 100’s of single-mode
horns. Simulations have been performed to predict the multi-mode optical response of the horn-lens configuration for
centre and off-axis pixels pertaining to each frequency band. The horn has been simulated to a high accuracy using the
Method of Moments. Using the horn simulation result as a source, the optical response of the lens has been examined
using the more approximate simulation technique; Ray-Launching Geometrical Optics (RL-GO). Solution accuracy and
simulation time depend heavily on the choice of RL-GO simulation parameters including: mesh size; the number of
launched rays; and how densely the horn source beam is sampled. Individual convergence studies have been performed
for each of these parameters and a final model has been obtained as a compromise between simulation time and
accuracy. The instrumental polarisation of the lens is predicted to be at the -50 dB level. Finally, the optimal location of
where to place the telescope focus in relation to the horn to maximise on-axis gain has been investigated. Several
techniques agreed that the ‘phase centre’ is around 20 mm behind the horn aperture at 140 GHz, increasing to 30 mm at
220 and 240 GHz. Taking into account beam truncation effects caused by the finite size of the telescope was found to
reduce the overall variation in on-axis gain.
We present the development and characterisation of a high frequency (500 – 750 GHz) corrugated horn based on stacked rings. A previous horn design, based on a Winston profile, has been adapted for the purpose of this manufacturing process without noticeable RF degradation. A subset of experimental results obtained using a vector network analyser are presented and compared to the predicted performance. These first results demonstrate that this technology is suitable for most commercial applications and also astronomical receivers in need of horn arrays at high frequencies.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.