Switchable active frequency selective surface (AFSS) absorber/reflector can work in opposite scattering state and be widely applied in the stealth field. At present, abundant researches on material design have been conducted to obtain excellent electromagnetic (EM) properties. However, there are few studies on the modulation effect of switchable AFSS absorber/reflector on the EM wave. In this paper, a time-domain digital-coding AFSS absorber/reflector is proposed to manipulate the spectral distribution of harmonic. The accurate control of each harmonic is achieved through AFSS modulating parameters. Then, a simple controller based on FPGA is designed. By coding “0” and “1” elements with controlled sequences, the AFSS can be switched flexibly in both absorbing and reflection states. On this basis, the imaging characteristics of time-domain digital-coding AFSS absorber/reflector are further analyzed, and distance transformation phenomena are described in detail. The SAR experiments are performed to demonstrate the required function of distance transformation.

Micro-Doppler characteristics have been widely utilized to discriminate the space targets. In this paper, the micro-Doppler parametric model (mDPM) is presented to fit the micro-Doppler characteristics of cone-shaped space targets. Then, the genetic algorithm-general parameterized time-frequency transform (GA-GPTF) method is proposed to estimate the parameters of mDPM accurately. Additionally, the ratio of the two parameters of mDPM is verified to be directly related to the physical attribute of scattering centers. It can be applied to discriminate the type of scattering centers quantitatively. Finally, the electromagnetic simulation and anechoic chamber experiment verify the accuracy of mDPM and the effectiveness of the scattering center discrimination method.

Echo cancellation is an ingenious method that protects the target of interest (TOI) by cancelling target echo at radar receiver with an active source. Recently the cancellation method using frequency and time-delay modulation has been proposed, considering the unavoidable processing time for the canceler when synthetic aperture radar (SAR) transmits large time bandwidth product signals such as linear frequency modulation pulses. Then the cancellation signal can cancel out the target echo even when it lags behind. However, echo cancellation also requires precise amplitude match of cancellation signal and target echo at SAR receiver. Amplitude match relies on accurate transmitting power calculation, which is difficult to guarantee considering prior information errors. In the presence of amplitude mismatch, the target echo cannot be completely cancelled thus remains visible in the SAR image. In this paper, we proposed an improved echo cancellation method based on nonperiodic interrupted sampling modulation, which produces high-level side lobes performing as a continuous jamming strip along range direction after matched filtering processing. By applying the proposed method, the residual of TOI in SAR image is covered by the jamming strip, thus a more robust echo cancellation is obtained in the presence of amplitude mismatch. Measured SAR data simulations demonstrate the effectiveness of the proposed method.

A synthetic aperture radar (SAR) image transform method is proposed based on random period amplitude and frequency shifting joint modulation. The random period amplitude sequence is designed to modulate the radar pulse signal so that the sidelobe of range profile is disordered with high level. Based on the spectrum property of random period amplitude sequence, the frequency shifting value can be obtained to conduct the joint modulation. Subsequently, frequency shifting is applied to move the high level sidelobe of range profile to the position of the target of interest (TOI). As a result, the TOI can be protected and false target image emerges, which shows both blanket and deception properties. By utilizing the joint modulation in fast time and amplitude modulation in slow time, the image of TOI is covered after SAR imaging. At the same time, the false images are generated in range and azimuth directions. Finally, simulations and SAR data experiments are conducted to obtain the transformed SAR image with proper amplitude sequence and frequency shifting parameters. The correlation coefficient between the transformed image and real target image is calculated, which indicates the validity of the proposed method.

Target echo cancellation is an ingenious method that protects the target of interest (TOI) from being detected by radar. Interrupted-sampling repeater jamming (ISRJ) is a novel deception jamming method for linear frequency modulation (LFM) radar countermeasures, which has been applied in target echo cancellation recently. Compared with the conventional cancellation method, not only can the target echo be successfully cancelled at radar receiver, but a train of false targets is also produced and forms deception jamming by applying the ISRJ technique. In this paper, an improved radar target echo cancellation method based on ISRJ is proposed that utilizes an extra frequency shifting modulation on the intercepted LFM radar signal. The jammer power is more efficiently utilized by the proposed method. Moreover, more flexible multi-false-target deception jamming can be obtained by adjusting the interrupted sampling frequency. The real target remains effectively protected by the false preceding target in the presence of amplitude mismatch of cancellation signal and target echo. Numerical simulations and measured data experiments are conducted to demonstrate the effectiveness of the proposed method.

In this paper, an inverse synthetic aperture radar (ISAR) image transform method is proposed by utilizing the unique property of joint intra-pulse and inter-pulse periodic-coded phase modulation. By extending the periodic-coded phase modulation to the azimuth dimension, the multiple false targets spread along both the range and azimuth directions, then makes the target of interest (TOI) indistinguishable thus get effectively protected. On this basis, the image transform properties and parameter design principles are further discussed. Finally, both numerical and measured Yak-42 aircraft data simulations are conducted to demonstrate the validity of the proposed method.