Stepped Frequency Signal-Based STAP for Airborne Distributed Coherent Aperture Radar.

Airborne distributed coherent aperture radar (ADCAR) coheres several flexible unit radars to form an equivalent large aperture radar for enhancing the signal gain, spatial resolution, and system reliability; however, the ultralong interelement spacing brings severe grating lobes, which will considerably deteriorate the performance of clutter suppression and target detection. To conquer this issue, we propose a stepped frequency signal-based space-time adaptive processing (STAP) approach for clutter and grating lobes suppression. The increased transmitting signal frequency can expand the space frequency and Doppler frequency of both target echo and clutter echo; therefore, the target and clutter can be distinguished through different expanded frequency ranges, and in turn, the grating lobes can be suppressed. To further reduce the peak sidelobe ratio of target response, an accumulated pattern synthesis approach is applied in both transmit and receive end; furthermore, to guide practical implementation, the influence of the nonideal factors, including gain errors, phase errors, platform control errors, and grid mismatch are analyzed to provide a feasible boundary for the algorithm. Simulations corroborate the superiorities of the proposed STAP approach for ADCAR.