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It is interesting to determine the direction of arrival (DOA) of signals in the presence of impulsive noise for monostatic multiple-input multiple-output (MIMO) radar. Inspired by the robust statis...

Multiple false target images deception is an effective strategy to protect vital military targets from detection and recognition by inverse synthetic aperture radar (ISAR). Previous research about it focuses mainly on the interrupted-sampling and sub-Nyquist sampling repeater jamming based on digital radio frequency memory (DRFM). The digital image synthesis (DIS) technique or scatter-wave modulation is used to simulate electromagnetic scattering of the real target. However, it is difficult to realize due to the high reconnaissance accuracy requirement and a heavy computational burden. Moreover, the protected target remains in the same location and the false targets’ amplitude envelope based on periodic modulation is relatively fixed, which is not conducive to deception. In this paper, an ISAR image modulation method based on coding phase-switched screen (PSS) is proposed against ISAR. The method uses the target bait made of PSS or attaches the PSS to the protected target surface to impose phase modulation onto the reflected signal. As a result, multiple false target images with verisimilar properties are formed around the protected target position when the reflected signal is received and processed by the victim ISAR. Besides, the protected target is concealed and the flexible amplitude control of false targets is achieved. The simulation results are performed to verify the effectiveness of the proposed method.

Target feature control on the synthetic aperture radar (SAR) image using the passive way is a challenging task in the field of SAR jamming. The conventional passive jamming devices such as corner reflectors and chaffs cannot achieve the flexible modulation of SAR target feature duo to their fixed scattering cross section. As a passive material, active frequency selective surface (AFSS) can dynamically control their electromagnetic characteristics and has been widely applied in the radar target stealth field. In this paper, a target feature modulation method based on AFSS is proposed against SAR. The method intermittently switches the scattering intensity of AFSS material and imposes periodic or random code amplitude modulation onto the radar signal. As a consequence, multi-false targets with verisimilar characteristics or cross-shaped areas are formed when modulated signal is received and processed by the victim SAR. Thus, the protected target is difficult to detect and identify by the SAR system. Microwave anechoic chamber experiments and measured SAR data simulations with different modulating parameters are separately conducted to demonstrate the effectiveness of the proposed method.

In recent years, the compressed sensing theory has been widely used in sparse aperture radar imaging. The inverse synthetic aperture radar (ISAR) imaging based on the sparse aperture echo of V-style frequency modulation (V-FM) waveform, which can mitigate the ambiguity appeared in range and velocity, has been proposed in this paper. After analyzing and interpreting the reason why the VFM signal pulse compression needs to use dual channels, we built the VFM waveform sparse echo model and analyze the causes of echo sparseness. A modified weighted compressive sensing (MWCS) algorithm is proposed to obtain high-resolution images under strong noise environment. The innovation of this paper lies in the new weighting method and the iterative reconstruction algorithm. The experimental results are shown to demonstrate the validity of the proposed method.

Synthetic aperture radar (SAR) image modulation is an effective method to protect a target of interest, and thus receives intensive attention. Currently, it still remains challenging to design an image modulation method capable of both flexibility and diversity in a passive way. In this letter, a two-dimensional (2-D) image modulation method based on phase-switched screen (PSS) is proposed against the SAR. The method imposes phase modulation onto the radar reflected signal by the PSS so that 2-D multifalse targets with verisimilar characteristics are formed around the protected target position when received and processed by the victim radar receiver. The theoretical analysis indicates that the amplitude and position of the generated multifalse targets are precisely controlled by the PSS modulating parameters. Moreover, the protected target is concealed and cannot be detected by radar. Simulations and experimental results are conducted to illustrate the validity of the proposed method.

Interrupted-sampling repeater jamming (ISRJ) provides a novel coherent-jamming mode against wideband radar. ISRJ allows the single-antenna jammer to periodically sample and repeat a fraction of the intercepted signal, which reduces the sampling rate and achieves transmit-receive isolation. The coherent-jamming signal generated by ISRJ can form multiple verisimilar false targets when received and processed by the victim radar receiver. Moreover, some false targets can precede the real target. This paper surveys the use of ISRJ in linear frequency modulated (LFM) radar jamming. The theory and application of ISRJ has been researched for more than one decade, but what is missing is a completed summary for the framework of this technique. In this paper, mathematic principles of ISRJ against LFM radars, which utilize matched-filter processing, stretch processing, and range-Doppler processing, are developed. The unique jamming effects in radar systems are focused on when the interrupted sampling frequency of the jammer is smaller than the bandwidth of the radar signal. Specifically, the false-target characteristics, including amplitude, space distribution, and phase, are discussed, respectively. On this basis, the key jamming elements, which determine these false-target characteristics, are pointed out and analyzed in detail. At last, simulation and real data are used to verify the correctness of the analyses. Experimental results highlight the potential application of the proposed jamming mode.

Micro-motion dynamics, such as rapid rotation, vibration and spinning motion, impose additional time-varying frequency modulation on the returned radar signals, which is known as the micro-Doppler (m-D) effect. Micro-Doppler frequency is considered as a stable and unique feature, where the uniqueness means that different micro-motions have distinct signatures. Thus, radar m-D feature extraction is of great potential in target classification and identification. This paper presents m-D frequency estimation from the HRRPs of rotating targets in frequency-stepped signal (FSS) based on the circular correlation (CC) coefficients and the circular average magnitude difference (CAMD) coefficients. The m-D frequency of rotating targets can be estimated accurately from the two proposed methods and the corresponding computational cost burden is also investigated. The accuracy and efficiency of the estimations are compared and revealed by the simulated trials and experimental data.

The influence of intelligence gathering inaccuracy, especially the estimate error of radar kinematic parameter, on the performance of deceptive jamming against synthetic aperture radar (SAR) is studied in this paper, filling a knowledge vacancy in the field of SAR electronic countermeasures. For the first time, an equivalence relationship between non-ideal jamming and ground moving target is derived and verified in raw phase history data domain and radar image domain. A novel and elegant way to quantify the defocus and displacement of false target in radar image is proposed based on the equivalence relationship. Work presented in this paper can guide the design of jammer’s intelligence gathering subsystem and optimize jamming configuration, from the view of jammer. The results also avail electronic counter-countermeasures, from the view of radar.

Target micro-motions such as rotation and vibration introduce phase modulation, termed as micro-Doppler (m-D) effect, onto synthetic aperture radar (SAR) signals. This causes ghost targets in the reconstructed SAR images. Inspired by this unique characteristic, a passive-jamming method based on m-D was developed for SAR. The m-D jamming method utilised a rotating reflector to intentionally generate ghost targets as jamming strips on the SAR image so as to protect certain areas. The m-D jamming method based on a single rotating reflector can only generate a long jamming strip along the azimuth direction but located in a finite number of range cells, which restricts the region of protected scene. In this study, an improved m-D jamming method based on phase-switched screen (PSS) is proposed, which combines the advantage induced by the PSS modulation and the usefulness of the m-D jamming. By controlling the modulating frequency and waveform of the PSS, the jamming strip is enlarged along the range direction. Theoretical analyses and simulation results verify the validity of the proposed method.

The phase-switched screen (PSS) imposes phase modulation onto the radar-reflected signal so that its energy is redistributed into sidebands that lie outside the receiver pass-band. However, when illuminated by a wideband linear frequency modulation (LFM) radar, the modulated reflected signal may still occupy the radar pass-band if the LFM signal bandwidth is greater than the modulating frequency. Previous research about the reflectivity performance of a PSS against LFM radar illumination focuses mainly on the frequency spectrum characteristics. In this study, an investigation has been carried out to determine the matched-filter properties of an LFM radar signal modulated by a PSS. Theoretical analyses and simulation results have proven that even though the radar receiver bandwidth has been corrupted to aliasing by component of the reflected signal, the PSS is shown to be equally effective in shielding a target and additionally provide a multiple-decoy capability.

High-resolution range profile (HRRP) has been useful in the support of target characterization and thus receives intensive attention. It is still a challenging task to design a deception method capable of both generating false-target HRRPs and concealing the real-target HRRP. In this letter, an HRRP deception method based on phase-switched screen (PSS) is proposed. This method utilizes PSS to impose phase modulation onto the radar reflected signal so that multiple false targets with verisimilar HRRP characteristics appear symmetrically around the real-target position. Meanwhile, the real-target HRRP is concealed and may not be detected by radar. Experimental results are used to verify the correctness of the analyses.

Due to the sparsity of the space distribution of point scatterers and radar echo data, the theory of Compressed Sensing (CS) has been successfully applied in Inverse Synthetic Aperture Radar (ISAR) imaging, which can recover an unknown sparse signal from a limited number of measurements by solving a sparsity-constrained optimization problem. In this paper, since the V style modulation(V-FM) signal can mitigate the ambiguity apparent in range and velocity, the dual-channel, two-dimension, compressed-sensing (2D-CS) algorithm is proposed for Bistatic ISAR (Bi-ISAR) imaging, which directly deals with the 2D signal model for image reconstruction based on solving a nonconvex optimization problem. The coupled 2D super-resolution model of the target&rsquo, s echoes is firstly established, then, the 2D-SL0 algorithm is applied in each channel with different dictionaries, and the final image is obtained by synthesizing the two channels. Experiments are used to test the robustness of the Bi-ISAR imaging framework with the two-dimensional CS method. The results show that the framework is capable accurately reconstructing the Bi-ISAR image within the conditions of low SNR and low measured data.

Echo cancellation is of great potential for a radar cross section reduction in stealth technology. All the techniques developed in the last decade rely primarily on the assumption that cancellation echo and target echo synchronize in the time domain. However, the cancellation echo may lag behind the target echo when countering a synthetic aperture radar (SAR). This is because the cancellation echo generation requires extra processing time when the SAR transmits and receives large time bandwidth product signal such as linear frequency modulation pulses. Thus, the cancellation echo and target echo cannot cancel each other perfectly. In this paper, we develop a novel three-stage active cancellation method using frequency and delay-time modulation to cancel out the target echo. In this scenario, the cancellation echo will intentionally lag behind the target echo. Theoretical analyses and simulation results verify the effectiveness of the proposed method.

Digital false-target image synthesizer (DIS) has been proposed as a deceptive jamming method for countering inverse synthetic aperture radar (ISAR) with an RF imaging false-target capability. However, to efficiently generate jamming signal in real time, a specific-designed generator is unavoidable for the implementation of this algorithm, where parallel and pipeline processing are both included because jamming signal is generated according to each range bin. This paper proposes an improved two-stage DIS method (T-DIS). The implementation of the T-DIS can be effectively simplified by separating the modulation process of a repeat jammer into two stages: 1) the offline stage and 2) the real-time stage. The modulation signal can be easily extracted from the modulation-matrix buffered in the offline stage. Only an element-by-element matrix multiplication between the modulation signal and the intercepted ISAR signal is needed in the real-time stage. In contrast to the conventional DIS method, the proposed algorithm exhibits simplicity and flexibility significantly, which reduces the computation time and hardware constraints. Experimental results of scattering model of the Yak-42 plane and real data illuminate the validity of the proposed method.

As recently demonstrated, active echo cancellation (AEC) is potential in preventing target from being observed by radar. In this paper, a novel method capable of cancelling synthetic aperture radar (SAR) target echo is proposed based on a dual-antenna system utilizing sub-Nyquist sampling. The proposed method provides a capability of concealing SAR target and form a train of false targets simultaneously. First, the design of the dual-antenna active-echo-cancellation (AEC) system is presented. The principles of sub-Nyquist sampling are described. Then, the key parameters for sub-Nyquist sampling, i.e., the sampling rate and delay time are analyzed. At last, simulation results verify the effectiveness of the proposed method.

A novel radar target recognition method based on physical-statistical model is proposed, which uses sequences of full-polarization high resolution radar range-profiles (HRRP). The HRRP of target is modeled as a Middleton's Class A non-Gaussian distribution through a physical consideration. It is found that the model parameters describe the scattering physical characteristics of radar target and can be chosen as feature vector for radar target recognition. The Parzen window is adopted to estimate the probability distribution function of model parameter and the classifier is designed via Bayes theorem. The approach is applied to the classification of measured data. Numerical results have shown that the approach can extract the features which are not sensitive to target orientation and are effective to radar target recognition.