KEYWORDS: Modulation, Orthogonal frequency division multiplexing, Radar, Signal processing, Signal generators, Electronic filtering, Phase shift keying, Data transmission
Within research presented in this article, several radar waveforms were designed. Waveforms based on common simple and complex radiolocational signals were combined using OFDM (Orthogonal Frequency Division Multiplexing). Combined with the ever-increasing technological possibilities, OFDM can be a valuable tool to overcome the challenges of modern radiolocation, such as limited spectrum resources and the improvement of electronic intelligence (ELINT) and electronic warfare (EW) methods. Despite it has become quite common in today's radiolocation, OFDM still appears to be a innovative solution with high development potential and a lot of still unused possibilities. Due to above, an attempt was made to explore the properties of waveforms significantly differing from typical telecommunications modulations. Designed signals were subjected to the analysis of properties in the time and frequency domains using cross-sections of the ambiguity function. The results were compared with the properties of classic radar signals in a given frequency band. The goal of the simulations was to illustrate the potential benefits and losses in the time-frequency waveforms of the synthesized signal compared to classic solutions. Potential degradation of signal parameters is a particularly important issue for combined radar-communication systems. The proprietary element of the study is the synthesis and analysis of signals containing different types of modulation on individual sub-bands simultaneously. The collected results will be used for further research on the methods of synthesis and processing of radiolocation signals using OFDM technology.
In the classical radar processing chain detection and tracking are separate, consecutive processes. In the case of the large amount of detection the number of false alarms and in consequence the number of false plot-to-track associations highly increase. In such case it can be used one of the Track-Before-Detect (TBD) algorithms that connects the detection and tracking into one process. An important part of such method is the plots preselection during the track forming process which is related to track constraints. One of the simplest method is gating that eliminates unlikely observation-to-track pairings. The basic gates in the two-dimensional space are the rectangular one and elliptical one. In the article the comparison of the use of both shapes is presented. The number of false associations and the gating computational complexity is considered.
One of the tasks performed by contemporary radars is the classification of a type of detected objects. Among many types of objects, helicopters, and especially hovering ones, are of special interest in radar’s self-defence. The echo signal of such object possesses specific properties of its spectrum that result from the construction of the object. A characteristic property of the echo signal is the presence of the spectral components from the hull of the helicopter as well as from the main rotor. The parameters of the latter components depend on the rotary speed of the rotor, the number of the blades and their length.
Research work related to the design and use of anti-radiation missiles (ARM), and any systems intended to protect radar and other radiation-emitting installations against ARMs, requires access to theoretical and physical models of direction finding devices, which are used in guidance systems installed in the aforementioned missiles. In this work, the authors present the concept of an electromagnetic source seeker working in the microwave band. In the solution presented herein, the direction finding is accomplished using the phase method. Phase analysis of signals emitted by the observed microwave source is relatively fast due to the quadrature configuration of the microwave phase discriminator used for this purpose. During an attack, an anti-radiation missile moves at great speed, which exceeds 1000 m/s. Due to this fact, the missile needs to be equipped with systems, which are capable of estimating the direction of the targeted source, and which can update the relevant information as quickly as possible. Such properties in the presented concept were achieved by using comparators with analogue inputs and logical digital (0/1) outputs. As a result, the information from the direction finding channel is obtained in a digital format, with the number of bits (the resolution) being dependent on the number of applied comparators. The authors therefore assume that a coarse direction finding will be used when the deviation between missile trajectory and the direction of target source is relatively large, whereas the more precise target location estimation algorithm will be used when the trajectory of the missile is matched (within established limits) to the direction of the emission source.
KEYWORDS: Radar signal processing, Radar, Signal to noise ratio, Frequency modulation, Fourier transforms, Electronic signals intelligence, Signal detection
The paper presents a novel method for NLFM radar signal instantaneous frequency estimation. Up to now there are only a few limited reports in this field. The method involves combined short-time Fourier transform and IF curve smoothing in time – frequency plane. The algorithm performs a fine estimation of instantaneous frequency of noise buried signals up to -3 dB. Due to FFT and simple filtering application, there is no high computational load needed. Simulation results indicate that the algorithm is robust and outperforms well-known phase differentiation method.
In military radars a special attention is paid to fast moving targets and the ballistic objects. Detection, identification and tracking of such objects is a critical task in air surveillance radars, artillery radars and C-RAM systems. The development of algorithms that realize this aim requires testing many potential radiolocation situations. Preliminary tests can be realized using a software simulator of air picture generated by a radar. This article presents a simulator that is capable of generating the plots accordingly to the simulated radar’s operating mode and its operational parameters. The objects modeled in the simulator are among the others the ones with the ballistic trajectory. Except the objects’ plots there are generated the plots that result from false alarms. Every simulated plot contains the information about position (range, azimuth and elevation) and the value of the echo signal amplitude at the output of the detector. The principles of operation of the particular parts of simulator and selected results are presented.
This article presents CUDA architecture as an effective tool for the digital beam forming in radar system. The article contains the results of a series of tests, which verify the fulfillment of stability and data processing time requirements. In the article, the authors presents the results of implementations that illustrate different approaches to this issue and some methods to increase the efficiency of implemented algorithms. In addition, the presented results represent implementations on devices adapted for military applications.
Classic methods of detection of objects assume a certain threshold, that separates the echo signal of the object from noise. In case of objects with high linear velocity their echoes may be spread in time and can be under the threshold. The reduction of the threshold should improve a probability of detection, but on the other hand it will increase the probability of false alarm. This side effect can be reduced using special methods usually referred to as Track-before-Detect. Their principle of operation base on the analysis of object’s state estimation in several subsequent scans of sensors’ observation space. Subsequently the estimates of the object position are combined in accordance to assumed strategy. If the parameter of association cost achieves the threshold, it means that an object is detected. There are many TBD strategies described in the literature, but two of the most popular are the Multiple Hypothesis Tracking and the Dynamic Programming. The paper presents their principles of operation and a comparison of their effectiveness.
KEYWORDS: Field programmable gate arrays, Radar, Convolution, Filtering (signal processing), Logic, Electronic filtering, Process control, Control systems, Signal processing, Digital signal processing
In this paper some capabilities of field programmable gate arrays (FPGA) as a suitable platform for radar applications based on an exemplary implementation of matched filter are discussed. Relations between the resource usage, precision of calculations and design performance are presented. Results of a multi-aspect analysis can help in elaboration of specific implementation conclusions both at the stage of formulating processing algorithms and their implementation. A wider view of the possibilities and limitations of programmable logic in combination with the features of other available platforms leads to the effective use of modern heterogeneous systems, including FPGA, GPU and CPU, which in turn allows to take advantage of the possibilities and compensation for the limitations of those technologies.
KEYWORDS: Detection and tracking algorithms, Missiles, Radar, Algorithm development, Systems modeling, Algorithms, Data modeling, Electronics, Defense and security, Combustion
There are known only few ballistic object tracking algorithms. To develop such algorithms and to its further testing, it is necessary to implement possibly simple and reliable objects’ dynamics model. The article presents the dynamics’ model of a tactical ballistic missile (TBM) including the three stages of flight: the boost stage and two passive stages – the ascending one and the descending one. Additionally, the procedure of transformation from the local coordinate system to the polar-radar oriented and the global is presented. The prepared theoretical data may be used to determine the tracking algorithm parameters and to its further verification.
In this paper we present the concept of multiple sensors data acquisition from onboard of an Unmanned Air
Vehicule (UAV). Because of flight instabilities caused by atmosferic movements (winds, thermals etc..) it is necessary to
apply active stabilization in order to obtain reliable readings from observation sensors. The most stabilization-demanding
sensor is Synthetic Aperture Radar (SAR) and in this paper two methods of stabilization are presented: hybrid (electromechanical)
and electronic.
KEYWORDS: Sensors, Target detection, Antennas, Radar, Signal to noise ratio, Monte Carlo methods, Signal processing, Filtering (signal processing), Doppler effect, Analytical research
Space-Time Adaptive Processing (STAP) is a well known technique used for dealing with clutter in order to detect
moving targets. This technique was derived under assumption, that clutter has Gaussian characteristics.
Unfortunately when dealing with sea clutter, Gaussian assumption is no longer valid [1]. This causes increased
number of false alarms. In this paper we present improved detector to deal with non-Gaussian clutter. Detector was
derived from Generalized Likelihood Ratio Test (GLRT), assuming Spherically Invariant Random Process (SIRP) as
a model for the clutter. Resulting detector was named Two Dirac-Deltas (TDD) detector and it has additional
parameter (Δ) in comparison to classical STAP. Based on simulations, it is shown that it is crucial to choose Δ
parameter appropriately.
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