Synthetic aperture radar has found wide applications in many areas, e.g., battlefield awareness.However, SAR is vulnerable to various kinds of interference, among which narrow-band interference is commonly used.In this letter, an eigensubspace-based filtering approach is proposed for NBI suppression in SAR without using passive-sniff data as the reference signal.

Unmanned aerial vehicle (UAV) synthetic aperture radar (SAR) is very important for battlefield awareness. For SAR systems mounted on a UAV, the motion errors can be considerably high due to atmospheric turbulence and aircraft properties, such as its small size, which makes motion compensation (MOCO) in UAV SAR more urgent than other SAR systems. In this paper, based on 3-D motion error analysis, a novel 3-D MOCO method is proposed. The main idea is to extract necessary motion parameters, i.e., forward velocity and displacement in line-of-sight direction, fromradar raw data, based on an instantaneous Doppler rate estimate. Experimental results show that the proposed method is suitable for low- or medium-altitude UAV SAR systems equipped with a low-accuracy inertial navigation system.

A two-stage blind adaptive anti-jamming algorithm for global positioning systems (GPS) is proposed in this study. The new algorithm cancels interferences by projecting the array received signals on the orthogonal complement space of interferences. Then the algorithm utilises the CLEAN method to estimate direction of arrivals of GPS signals according to the period repetitive feature of GPS coarse/acquisition (C/A) code and form the multi-beam, where each beam can point one GPS signal. Test data and simulation results show the effectiveness of the new algorithm.

A beamspace adaptive planar array for broadband beamforming is proposed based on the frequency invariant beamforming technique. A detailed analysis is provided for both the linear arrays and the planar arrays, where two conditions are imposed: the beams should exhibit a good frequency invariant property and be linearly independent. These two conditions are not independent and there is a tradeoff between them. To improve the interference cancellation capability of the array, we may need to sacrifice the frequency invariant property to some degree for more linearly independent beams. A sufficient condition for the linear independence of the beams is derived with a DFT matrix based design proposed. Simulation results verified our analysis and the proposed method.