Yongcai Liu

Sub-Nyquist Sampling Jamming Against ISAR With Compressive Sensing

Shannon-Nyquist theorem indicates that under-sampling at low rates will lead to aliasing in the frequency domain of signal and can be utilized in electronic warfare. However, the question is whether it still works when the compressive sensing (CS) algorithm is applied into reconstruction of target. This paper concerns sub-Nyquist sampled jamming signals and its corresponding influence on inverse synthetic aperture radar (ISAR) imaging via CS. Results show that multiple deceptive false-target images with finer resolution will be induced after the sub-Nyquist sampled jamming signals dealed with CS-based reconstruction algorithm; hence, the sub-Nyquist sampling can be adopted in the generation of decoys against ISAR with CS. Experimental results of the scattering model of the Yak-42 plane and real data are used to verify the correctness of the analyses.

Features Extraction of Rotationally Symmetric Ballistic Targets Based on Micro-Doppler

It is potentially useful to perform target identification using micro-Doppler features because they contain information on the geometrical structure of the target. In this paper, the m-D effect of the rotationally symmetric ballistic target (BT) is analyzed which reveals that the m-D is not a form of sinusoidal modulation due to the slidingtype scattering. Inspired by the extended Hough transform (EHT), a method to extract all the six parameters of the BT is proposed. The m-D effect and the performance of feature extraction algorithm are demonstrated by the measured data in a microwave anechoic chamber.

Inverse Omega-K Algorithm for the Electromagnetic Deception of Synthetic Aperture Radar

Deceptive jamming against synthetic aperture radar (SAR) receives intensive interests during the past decade. However, it is still a challenging task to design a jamming method that is competent both in focus capability and in computational efficiency, especially in the case where jammer is confronted with SAR with significant squint angle and long synthetic aperture. In this paper, we propose an inverse omega-K algorithm and present an accurate and an approximate implementation scheme of the algorithm. The accurate scheme can achieve full focus with no regard to the squint angle and synthetic aperture of radar. Its computations include fast Fourier transform (FFT), Stolt interpolation, and complex multiply. Advantage of computational efficiency can be achieved under assumption that the support region of radar can be crudely evaluated a priori so that the most time-consuming Stolt interpolation can be done offline. The support region is determined by carrier frequency and bandwidth of radar signal, pointing direction, and azimuth beam width of radar antenna. For the case in which the support region of radar is not available to jammer beforehand, the approximate scheme is a remedy. By substituting the Stolt interpolation with Chirp-Z transform (CZT), the approximate scheme is readily fit for parallel computation and hence appealing for its high efficiency. However, the focus criterion exerts a limitation on range scale of electromagnetic deception when the squint angle of SAR is large. Both implementation schemes are verified by simulation results.

Signature Extraction From Rotating Targets Based on a Fraction of HRRPs

Motion or structure signatures, extracted from radar echoes, are of great potential in target identification. Traditional techniques for signature extraction rely primarily on the assumption that the time series of the signal contains at least one oscillation or more during the illumination time. However, as many applications involve short duration signals or long duration signals, they are only partially useful in real-world scenarios. The conventional signature extraction algorithms may suffer from degraded precision. This paper presents a three-point model for signature extraction availing the characteristics of the high resolution range profiles (HRRPs) of rotating targets with stepped-frequency signal (SFS). The frequency and the length of rotating targets can be estimated accurately from a fraction of the HRRPs in slow-time-range plane. The accuracy and efficiency of the estimation are demonstrated by simulated and experimental trials.

A Three-Stage Active Cancellation Method Against Synthetic Aperture Radar

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.

Micro-Doppler period estimation from ballistic targets with precession

Radar micro-Doppler (m-D) signatures for target recognition have received increasing attention among the radar community. Since warheads, decoys and debris have unique m-D signatures, m-D parameter estimation has great potential in ballistic missile defense (BMD) applications. In the case of ballistic targets (BTs) with rapid precession, the conventionally sinusoidal modulation of m-D effect is disturbed by the sliding-type scattering. Thus, extraction of micro-motion signatures based on the sinusoidal form of time-frequency representation (TFR) may become difficult. In this paper, the circular average magnitude difference (CAMD) coefficients are employed to provide an estimation of the precession period due to the periodicity of TFR. Effectiveness of the proposed estimation method is demonstrated by the simulation data.

Raw Signal Simulator for SAR With Trajectory Deviation Based on Spatial Spectrum Analysis

This paper presents a whole new method for simulating a raw signal of synthetic aperture radar (SAR) with trajectory deviation. In this paper, a SAR raw signal is viewed as a spatial function in terms of radar location, at a fixed range frequency component of the radar signal. It is disclosed and verified that the SAR raw signals is band limited from the perspective of spatial spectrum analysis. Based on this finding, SAR raw signals under condition of trajectory deviation are obtained by interpolating the SAR raw signal along a set of ideally linear trajectories. The unprecedent performance achieved by the new method mainly includes the following. First, it provides a way to update existing simulators designed for ideally linear trajectory, giving them the capability to take trajectory deviation into consideration. Second, it is an efficient SAR raw signal simulator whose validity limit is greatly expanded compared with existing efficient simulators, as many constraints are eliminated without sacrificing computational efficiency or phase accuracy. Third, it is a uniform framework applicable for multiple SAR acquisition modes. Finally, the computational complexity of Monte Carlo experiment under various trajectory deviations is dramatically reduced, at the expense of storage memory requirement. Theoretical analyses are demonstrated by experimental results.

A Unified Multimode SAR Raw Signal Simulation Method Based on Acquisition Mode Mutation

Raw signal simulators for synthetic aperture radar (SAR) in different acquisition modes have been studied individually. This letter is dedicated to presenting a method for simulating multimode SAR raw signal in a unified framework. To this end, we first simulate stripmap SAR raw signal, and then mutate the raw signal from stripmap mode into the desired acquisition mode. The acquisition mode mutation is implemented by azimuth-time-variant and range-frequency-dependent bandpass filtering. While processing in range-frequency domain brings forth high accuracy, processing in azimuth-time domain makes the method applicable for flexible antenna steering laws specified by multiple SAR acquisition modes, such as staring spotlight mode, sliding spotlight mode, and terrain observation by progressive scans mode. The proposed method is validated by the simulation results.

Transmitter power comparison between incoherent noise and coherent deceptive jamming against synthetic aperture radar

During the rapid development of synthetic aperture radar (SAR), jamming techniques against SAR have aroused intensive study interests in the field of electronic counter measures (ECM). In this paper, we compare the jammers transmitter power required by coherent deceptive jamming against SAR and by incoherent noise jamming against SAR. It is pointed out that, in order to yield same jamming-to-signal ratio (JSR) in SAR image domain, the ratio of the transmitter power of incoherent noise jamming to that of coherent deceptive jamming should be the average pulse compression gain (APCG), rather than, the pulse compression gain (PCG) in SAR image formation processing, which is different from the opinion of some literatures. Theoretical analyses are verified by simulation results.

Influence of Estimate Error of Radar Kinematic Parameter on Deceptive Jamming Against SAR

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 jammers intelligence gathering subsystem and optimize jamming configuration, from the view of jammer. The results also avail electronic counter-countermeasures, from the view of radar.