The Chinese first fully polarimetric space-borne synthetic aperture radar (SAR)-Gaofen-3 (GF-3) was launched in August 2016, which operates at the C-band and the resolution can reach 1 m. Polarimetric SAR calibration is a procedure that corrects the polarization distortion of a measured scattering matrix by referring to the scattering matrix of a known target. The present paper describes the principle, design, manufacture, and measurement results of a novel polarimetric active radar calibrator (PARC) designed for GF-3. A new design method for PARC was presented and two dual-polarized antennas with very high polarization purity were used. The internal calibration technique was introduced to ensure balance in the amplitude and phase, which ensures the precision of the PARC’s scattering matrices. The results we obtained through measurement in the microwave anechoic chamber and experiments in in-orbit calibration agree well with the theoretical predictions, and the novel PARC presented is proved to be well suited for polarization and radiometric calibration of GF-3.

A chirp-mismatch echo signal can be generated by exchanging the I and Q baseband signals of a received SAR signal. In this paper, the basic generation principles of a chirp-mismatch echo signal are analyzed. Then, a suppression jamming method with controllable jamming position and coverage area is proposed. This method firstly performs chirp-mismatch processing on the received SAR signals, then controls the range jamming coverage and center position through range shift-frequency modulation and time delay, and controls the azimuth jamming coverage and center position through motion modulation and azimuth shift-frequency modulation. Theoretical analysis and simulation results show that this method can effectively control the location and coverage of a jamming result without convolution modulation, and it is easy to implement in engineering. The simulation results verify the correctness of the theoretical model, which can provide a basis for the implementation and application of SAR jamming based on the active radar transponder.

The convolution modulation jamming method based on noise template has received widespread attention and application due to its advantages such as having the ability to obtain synthetic aperture radar (SAR) system processing gain. However, there are few studies on the evaluation analysis and optimization design of noise templates. In this letter, an optimal noise template generation method based on weighted combination is proposed and the multiscale structural similarity (MS-SSIM) index is used to evaluate the jamming effect of the obtained optimal noise template. The experimental results show that the optimal combination noise template can achieve better jamming effect than traditional noise templates under the same jamming-to-signal ratio (JSR), which verifies the effectiveness of the proposed method.

More and more devices access the wireless network with the development of wireless communication, making device security a widespread concern. Specific emitter identification (SEI) is significant for the authorization and security of wireless devices and instrumentation. Aiming at improving the identification performance for a large number of wireless devices, a novel deep fusion framework for SEI, named DFDK-MSNet, is proposed. It organically integrates domain knowledge (DK) and multiscale deep networks. The DK is deeply injected into the DFDK-MSNet at the stages of signal decomposition and radio frequency (RF) fingerprint characterization. It is evaluated whether the signal decomposition results are most conducive to individual difference characterization based on the DK of RF mechanism. A multiscale 1DCNN is proposed to extract more subtle and comprehensive features further at a multi and deep level, with the texture RF fingerprint of DK as the input. Massive experiments on a real-world dataset are conducted to verify the effectiveness and superiority of the proposed method, which can greatly increase the number of devices to be identified while ensuring high accuracy. It achieves an identification accuracy above 88% for identifying 60 transmitters even belonging to the same model and batch. The proposed method improves the accuracy by 8% for 60 emitters compared to the comparative methods, and the convergence speed is significantly accelerated with the stable convergence epoch being only 1/6 of the comparative methods. It is significant for the practical authorization scenarios of wireless devices.

The forwarding (repeater) jamming has been widely used in Synthetic Aperture Radar (SAR) countermeasures. However, when the jammer has a time division requirement for reception and transmission, the operation that the jammer first receives the entire SAR pulse and then transmits the jamming signal will result in a long forwarding delay. Especially for spaceborne SAR with a pulse duration of tens of microseconds, the long delay means that the jamming can only cover areas several kilometers away from the jammer, and targets close to the jammer are difficult to protect. To address this issue, a partial-pulse-reception and full-pulse-recovery jamming scheme is proposed in this paper. The core of this scheme is to recover the partial pulses intercepted by the jammer into a pulse with a complete pulse duration. A pulse recovery method based on two-dimensional joint parameter estimation is proposed, in which the problem of pulse recovery is transformed into a parameter estimation problem for single tone signals. In addition, with the help of processing tools such as wave gate limitation and Kalman filtering, the robustness of this method is improved and it can still work at an SNR as low as -30dB. The effectiveness of the proposed method is verified through experiments using measured and simulated data under different SNR conditions.

Over the past decade, IECAS (Institute of Electronics, Chinese Academy of Sciences) has developed a set of L-, S-, C-, and X-band active radar calibrators that are deployed during the calibration campaigns for HJ1C synthetic aperture radar (SAR), Gaofen-3 SAR, and so on. In the near future, P-band and Ka-band spaceborne SARs will be launched. We found that it is not convenient to develop special active radar calibrators (ARCs) for a specific SAR or a specific frequency band SAR, and the acquired experience could help in the design and development of a multi-band ARC. This paper describes the design and implementation of a multi-band active radar calibrator which can operate in the L-, C-, X-, and Ka-bands. Moreover, laboratory measurements are performed to characterize the performance of the multi-band ARC, paying particular attention to the gain stability, the system transfer function, the gain flatness, and the linearity of the ARC receiver. Three such ARCs are developed, and to our knowledge, the multi-band ARC is the first of its kind in China or even in the world, and it can be used to implement the calibration campaigns of the Chinese Gaofen-3 SAR, Shenzhen-1 SAR, Luojia-2 SAR, and so on.