The problem of ground target detection with passive radars is considered. The design of an antenna array based on commercial elements is presented, based on a non-uniform linear array optimized ...according to sidelobe level requirements. Array processing techniques are applied in the cross-ambiguity function domain to exploit integration gain, system resolution and the sparsity of targets in this domain. A modified two-stage detection scheme is described, which is based on a previously-published one by other authors. All of these contributions are validated in a real semiurban scenario, proving the capabilities of detection, the direction of arrival estimation and the tracking of ground targets in the presence of big buildings that generate strong clutter returns. Detection performance is validated through the probability of false alarm and the probability of detection estimation with specified estimation errors.
In this article, a commercial low cost solution for increasing DVB-T based passive radar (also referred to as passive coherent location) robustness with respect to channel allocation and range ...resolution, is designed. IDEPAR demonstrator is updated to include a new recording system in charge of DVB-T channels reallocation. The use of commercial hardware introduces frequency mismatching between acquired channels that compromises system operation. To face channel frequency alignment, fulfilling the requirements imposed by the high Doppler resolution typical of passive radars, a novel compensation algorithm is proposed, based on the minimization of signal dispersion in the Cross-Ambiguity Function domain. The well-known cyclic prefix van de Beek method is used as reference. Results show an increase in target signal to interference ratio and detection performances, as well as a reduction of clutter dispersion when the novel proposed algorithm is applied. The low cost solution is also compared to a high performance one capable of acquiring a wide bandwidth of sparse DVB-T channels, and performing channel reallocation by digital signal processing. Results show that both systems reached similar performances in terms of range resolution and SNR improvement.
Ultra high frequency (UHF) passive ground clutter statistical models were determined from real data acquired by a passive radar for the design of approximations to the Neyman-Pearson detector based ...on machine learning techniques. The cross-ambiguity function was the input space without any preprocessing. The Gaussian model was proved to be suitable for high Doppler values. Other models were proposed for Doppler close to zero, where ground clutter and low bistatic Doppler targets concentrate. Likelihood ratio detectors were built for this Doppler region, and a neural-network-based adaptive threshold technique was designed for fulfilling false alarm requirements throughout all the input space. The proposed scheme outperformed a conventional passive radar one and could be used as a reference for future designs.
Passive radars exploit the signal transmitted by other systems, known as opportunity illuminators (OIs), instead of using their own transmitter. Due to its almost total invulnerability to natural ...disasters or physical attacks, satellite OIs are of special interest. In this line, a feasibility study of Earth Observation Synthetic Aperture Radar (EO SAR) systems as OIs is carried out taking into consideration signal waveform, availability, bistatic geometry, instrumented coverage area and incident power density. A case study based on the use of PAZ, the first Spanish EO SAR, is presented. PAZ transmitted waveform, operation modes, orbit characteristics and antenna and transmitter parameters are analyzed to estimate potential coverages and resolutions. The study concludes that, due to its working in on-demand operating mode, passive radars based on PAZ-type illuminators can be proposed as complementing tools during the sensor commissioning phase, for system maintenance and for improving its performance by providing additional information about the area of interest and/or increasing the data updating speed, exploiting other sensors during the time PAZ is not available.
New satellite constellations for broadband Internet service emerge as promising illuminators of opportunity for the of passive radar (PR) applications. Their wideband signals, high power flux at ...ground level, and theoretical global availability anticipate ameliorated performance compared to preexisting satellite-based PRs. On the other hand, the constellation deployment in low Earth orbits generates favorable movements for the radar imaging of the Earth's surface. In this article, the Starlink constellation is considered for the formation of passive SAR images. The Starlink datalink concerning the data transmission from the satellite to the user's terminal is selected as the illumination signal. The users' downlink signal characteristics are studied using experimental data from a dedicated measurement campaign, confirming its suitability for radar applications. Then, the time-variant radar geometry and the passive SAR processing scheme are described. A back projection radar image formation approach is selected to tackle the complexity of the bistatic geometry. The system validation is performed in a second measurement campaign concerning dual-channel measurements using the Starlink-based PR demonstrator developed at the Warsaw University of Technology. The first Starlink-based passive SAR images are obtained under direct satellite illumination of the PR deployment area and under adjacent-cell illumination conditions. The experimental results confirm the feasibility of exploiting Starlink transmissions for the formation of passive SAR images of urban areas.
Passive bistatic radars (PBRs) sensors are emerging technologies that have sparked interest due to the advantages derived from the use of opportunity illuminators instead of dedicated transmitters. ...An important research effort is being carried out, mainly focused on the analysis of the illuminators waveforms and the development of system demonstrators, being the detection and tracking of low flying aircrafts the most extended validation scenario. IDEPAR is a digital video broadcasting-terrestrial (DVB-T)-based multichannel PBR technological demonstrator, developed in the University of Alcalá. The main contributions of this study are the radar scenario, detection of terrestrial vehicles in semi-urban environments, and the development of a general and complete design methodology, that will allow the definition of system design requirements for any system and application. To validate system performance, real data were processed and detection and tracking results were evaluated using global positioning system data from cooperative targets. Reference signal processing algorithms were used. Results showed the feasibility of DVB-T-based PBRs for detecting and tracking low speed terrestrial vehicles in semi-urban scenarios.
Artificial intelligence techniques were applied for detecting small moving targets in maritime clutter environments. Neural detectors are considered to approximate the Neyman–Pearson (NP) in ...composite hypothesis testing problems. Sub-optimum approaches based on the Constrained Generalized Likelihood Ratio (CGLR) were analysed, and compared to conventional implementations based on Doppler filtering that are designed to filter clutter and improve the Signal-to-Interference Ratio, and Constant False Alarm Rate techniques. The CGLR performance was significantly better at the expense of a high computational cost. As a solution, neural network training sets were designed for approximating the NP detector. The detection of small boats in Gaussian clutter was the defined case study in order to assume the design hypothesis of the conventional solutions and to study their performance under their most favourable conditions. Detection schemes were evaluated using real radar data. Neural solutions based on Second Order Neural Networks provide the best results, being able to approximate the CGLR with a significantly low computational cost compatible with real-time operations.
•Artificial Intelligence techniques were applied for small boats radar detection.•Doppler radars and the constrained-GLR test were analysed and used as references.•MLPs, RBFNNs and SONNs were proposed and validated using simulated and real data.•SONNs improved radar Doppler performance and approximated the constrained-GLR test.•SONN computational cost study proved its feasibility in real time applications.
In this paper, the impact of the drone airscrews signature in passive radars exploiting Digital Video Broadcasting signals is tackled. Beamforming techniques optimized to minimize the variance of the ...interference using the statistical characterization of real clutter data followed by a CFAR detector are used to detect drones and their associated airscrews signature. An independent bi-dimensional tracker based on the Kalman filter is proposed to tackle the drone and airscrews tracking process, and to extract micro-Doppler signature features. Real radar data acquired by a technological demonstrator developed at the University of Alcalá were used to evaluate the proposed solution. Results proved the suitability of the proposed detection and tracking schemes for airscrews signature feature extraction. Ansys HFSS electromagnetic simulator validated the results.
Global Positioning System (GPS) satellites offer promising opportunity for Passive Radar systems due to their global coverage and the availability of multiple satellites throughout the world. ...However, their low power at ground level limits system coverage. In this paper, a GPS based Passive Radar which exploits a single illumination source, and uses digital array processing for ground targets localization is presented. To face signal power problems, a processing scheme combining reconstructed reference signals, adaptive filtering techniques and spatial filtering is implemented. Conventional beamforming techniques are used to increase the level of the target echo before the detection stage, and high resolution DoA estimation techniques are applied to estimate targets azimuth. Ground target localization in local Cartesian space is performed taking into account the system geometry, range and azimuth information. Both synthetic and real radar data are used to analyse system operation. During the measurement campaign, a cooperative vehicle was used for validation purposes. Results confirm that ground targets detection and localization are feasible using a single GPS transmitter.
In this paper, the improvement of the detection capabilities of Passive Radars (PRs) exploiting Digital Video Broadcasting signals for small drone detection is tackled. Beamforming techniques ...optimized to increase the Signal-to-Interference Ratio (SIR) are applied in a two-stage frequency-domain spatial filtering processing scheme. Real radar data acquired by a technological demonstrator developed at the University of Alcalá were used to validate the proposed solution. The optimum beamforming depends on the interference model. Considering the Cross-Ambiguity Function (CAF) output as the input space, a statistical analysis of clutter return was carried out for each array element. Results proved that clutter statistics depend on the array element, and are a function of the Doppler shift in the CAF area close to the zero Doppler, so optimum beamforming weights are estimated for each Doppler region and array antenna. Detection performance evaluation confirmed the expected improvement in SIR and its positive impact in small drone detection.
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