Medium pulse repetition frequency (MPRF) is an important mode in airborne radar system. Since MPRF mode brings both Doppler and range ambiguities, it causes difficulty for the airborne radar to suppress ground or sea clutter. In recent years, it has been pointed out that the frequency diverse array (FDA) radar is capable of separating the range ambiguous clutter, which is helpful for the airborne radar in detecting weak moving targets originally buried in ambiguous clutter. To further improve the ambiguous clutter separation performance, an enhanced pre-STAP beamforming for range ambiguous clutter suppression is proposed for the vertical FDA planar array in this paper. With consideration of range dependence of the vertical spatial frequency, a series of pre-STAP beamformers are designed using a priori knowledge of platform and radar parameters. The notches of the beamformers are aligned with the ambiguous clutter to extract echoes from desired range region while suppressing clutter from ambiguous range regions. The notches can be widened by using covariance matrix tapering technique and the proposed method can improve the performance of range ambiguous clutter separation with limited degrees-of-freedom (DOFs). Simulation examples show the effectiveness of the proposed method.

The extraction of scattering centers is a key step in 3D imaging of interferometric inverse synthetic aperture radar (InISAR). Due to the influence of background noise and sidelobes, existing methods often cannot achieve accurate extraction of scattering centers, resulting in outlier or loss of point clouds in the reconstructed 3D images. To solve this problem, we propose a robust scattering center extraction method based on range-azimuth profile reconstruction. First, a 1D range profile and a 1D azimuth profile are reconstructed based on autocorrelation matrix eigenvalue decomposition to suppress the background noise, and then a threshold is determined based on our proposed threshold updating mechanism to extract the scattering center accurately. The effectiveness and superiority of the proposed method are verified by the simulation results and experimental results based on real data.

This paper proposes a high-precision angle estimation method based on transmit sum and difference beamforming for coherent frequency diverse array (FDA) radar. By employing a small frequency offset across the array aperture, the coherent FDA radar achieves a range-angle-coupled transmit beampattern that combines wide transmission coverage with narrow reception capability. The proposed method constructs an equivalent two-dimensional coupled sum-difference beam in the target output channel by simultaneously utilizing signal detection outputs from multiple transmitted beams. This approach maintains the inherent advantages of FDA systems while enabling accurate angle estimation without sacrificing coverage. Simulation results demonstrate that the proposed architecture achieves an angular resolution of 1/20 of the beamwidth at a signal-to-noise ratio (SNR) of 20 dB, significantly outperforming conventional techniques. The method exhibits robust performance in various scenarios, which makes it a good candidate for modern radar applications requiring both wide-area surveillance and high-precision angle measurement.