Phase modulation technique is of great potential for generating jamming signal in electronic countermeasures. It is still a difficulty to devise a kind of jamming signal capable of generating both false targets deception jamming and barrage jamming. Attentions must be paid to phase modulation patterns and phase values. Inspired by scatter-wave jamming and phase modulation, an active jamming technique against inverse synthetic aperture radar (ISAR) is proposed based on periodic binary phase modulation in this paper. By imposing the periodic binary phase value (0 or π) onto the intercepted radar signal, the frequency properties of radar signal are changed, which result in the corresponding changes on the target echo. Accordingly, the imaging results are reformatted comparing with the target image. Radar pulses are sampled and phase-modulated in the fast time domain as well as the slow time domain, and then the jamming pulses are retransmitted to the target. After ISAR imaging, the false target images are induced. The principle and process of phase modulation are studied in detail. Then, the imaging model of jamming signal is established and the analysis of jamming effects are carried out. The simulation results with single scattering point and real data experiments with a ship show that both deception jamming and barrage jamming can be obtained. The theoretical analysis and simulation results prove the validity of the active jamming technique.

As many target characteristics can be extracted from the echoes by inverse synthetic aperture radar (ISAR), the jamming signal on ISAR need to simulate the electromagnetic scattering characteristics and kinematics characteristics with high fidelity. Based on the principle of periodic 0-π phase modulation, a method generating 2-D ISAR group targets is proposed. Radar pulses are sampled and modulated according to periodic 0-π phase sequence by the escort free-flight jammer, and then the modulated signals are retransmitted to the protected target, which can generate verisimilar false target images in ISAR. After the principle of escort free-flight jamming is introduced, the theory of periodic 0-π phase sequence is expounded. The generation process of jamming signal is analyzed. According to the 2-D output expression, the jamming effects with different modulation parameters are demonstrated. A theoretical study is carried out to determine the number, amplitude and space distribution of false targets. Experimental results of scattering model of an aircraft illuminate the effectiveness and correctness of the proposed method.

This article introduces a hybrid design method for high-efficiency absorbing Reconfigurable Transmitarray (ARTA). By cascading an absorbing layer with a 2-bit reconfigurable layer, the transmission unitcells can realize the frequency response characteristic of an Absorbing-Transmissive-Absorbing (A-T-A). Specifically, the frequencies with an absorption rate exceeding 80% are within the ranges of 3.3GHz-5.1GHz and 7.8GHz-9.4GHz, while the frequency range with transmission exceeding -3dB spans from 5.69GHz to 5.92GHz. Meanwhile, the transmission phase can be adjusted among four states: 0°, 90°, 180°, and 270°, enabling beam steering of ARTA. Compared to designs for non-reconfigurable transmissive arrays, our design methodology necessitates the satisfaction of absorbing performance under different phase states. For validation, A prototype sample, comprising a 12x12 array structured with 5 metallic layers and 4 dielectric layers, sandwiching an air layer in between, has been fabricated and tested. Measurement results demonstrated high radiation performance with a peak gain of 21.6 dB and aperture efficiency of 33.3% at 5.85 GHz. The BW-1 dB and BW-3 dB were 0.2 GHz and 0.6 GHz, respectively. ±60° 2D-scanning was achievable and when the beam is directed at 0°, the sidelobe levels in the E-plane and H-plane are -17.3 dB and -18 dB, respectively. Under normal incidence of an x-polarized wave, the -8 dB Monostatic RCS reduction bandwidths covered 32.1% (3.4-4.7 GHz) for lower band and 10% (8.5-9.4 GHz) for upper band. The ARTA by this hybrid design methodology represents an attractive solution for addressing electromagnetic compatibility issues and for low-detectability applications.

Superpixel methods are widely used in the processing of synthetic aperture radar (SAR) images. In recent years, a number of superpixel algorithms for SAR images have been proposed, and have achieved acceptable results despite the inherent speckle noise of SAR images. However, it is still difficult for existing algorithms to obtain satisfactory results in the inhomogeneous edge and texture areas. To overcome those problems, we propose a superpixel generating method based on pixel saliency difference and spatial distance for SAR images in this article. Firstly, a saliency map is calculated based on the Gaussian kernel function weighted local contrast measure, which can not only effectively suppress the speckle noise, but also enhance the fuzzy edges and regions with intensity inhomogeneity. Secondly, superpixels are generated by the local k-means clustering method based on the proposed distance measure, which can efficiently sort pixels to different clusters. In this step, the distance measure is calculated by combining the saliency difference and spatial distance with a proposed adaptive local compactness parameter. Thirdly, post-processing is utilized to clean up small segments. The evaluation experiments on the simulated SAR image demonstrate that our proposed method dramatically outperforms four state-of-the-art methods in terms of boundary recall, under-segmentation error, and achievable segmentation accuracy under almost all of the experimental parameters at a moderate segment speed. The experiments on real-world SAR images of different sceneries validate the superiority of our method. The superpixel results of the proposed method adhere well to the contour of targets, and correctly reflect the boundaries of texture details for the inhomogeneous regions.