Range-Ambiguous Clutter Suppression for STAP-Based Radar With Vertical Coherent Frequency Diverse Array

Forward-looking mode for moving target detection is important for airborne radar systems, however, it is difficult to suppress the range-dependent clutter in the presence of range ambiguity using the traditional space-time adaptive processing (STAP) techniques. In this article, a vertical coherent frequency diverse array (FDA) radar using quadratic phase coding (QPC) is proposed to alleviate the range-ambiguous clutter problem. The proposed vertical coherent FDA radar has two major advantages: 1) it uses an identical baseband waveform for each transmit element, which prevents the unreal orthogonal waveform assumption in the multiple-input multiple-output (MIMO) framework and 2) it achieves wide spatial coverage in elevation within a single-pulse duration, which is desirable for the airborne reconnaissance radar. The space-frequency-coupled characteristic of vertical coherent FDA is revealed and a series of two-dimensional (2-D) matched filters are designed, which is helpful for range-ambiguous clutter separation. Based on the QPC technique, the residual clutter is suppressed by orthogonal projection (OP) filtering, which further improves the target detection performance. With the proposed vertical coherent FDA using QPC, the range-ambiguous clutter can be separated successfully, and the clutter suppression performance is improved. Simulation results are presented to verify the effectiveness of the proposed method in serious range-ambiguous clutter scenarios.