Clutter Suppression for Spaceborne FDA-MIMO Radar With QPC

Clutter of medium Earth orbit (MEO) spaceborne radar (SBR) exists inherently range ambiguity due to high orbital altitude and range dependence induced by Earth's rotation, which would cause clutter spectrum spreading, thereby significantly deteriorating clutter suppression performance of conventional space-time adaptive processing (STAP). In response, this paper investigates a frequency diverse array (FDA) multiple-input multiple-output (MIMO) radar with quadratic phase coding (QPC), wherein a transmit-range dimension sample selection strategy is devised. Firstly, the proposed method formulates QPC to implement slow-time phase modulation across FDA-MIMO transmit channels, which circumvents complex orthogonal waveform design since frequency domain orthogonality can be attained by extending the frequency increment. Subsequently, leveraging the approximately linear coupling characteristic between mainlobe clutter Doppler frequency and range in MEO SBR, QPC decoding is implemented at the receiver to achieve Doppler shifting and clutter spectrum alignment across different range-ambiguous regions, effectively reducing clutter spectrum broadening. Furthermore, to alleviate the insufficiency of independent and identically distributed (i.i.d.) training samples in nonhomogeneous clutter environment, transmit data extracted from FDA-MIMO radar are incorporated as supplementary training samples. An enhanced clutter-plus-noise covariance matrix (CNCM) is then estimated by exploiting transmit-range dimension data, improving STAP filtering performance in the receive-Doppler domain for range-dependent clutter mitigation. Numerical experiments are conducted to validate the effectiveness of the proposed approach in suppressing range-ambiguous nonhomogeneous clutter for MEO SBR.