Adaptive Space-Time Radar Techniques and Waveforms

Energy-on-target is maximized in optics and ocean acoustics by transmitting a time-reversed (spectral phase conjugated) version of received data at each array element or subarray. This process uses an unknown propagation channel as its own space-time matched filter to implement a RAKE receiver at the target location. (A RAKE receiver passes data through a filter that is matched to the channel impulse response.) Several techniques for improving the phase conjugation process for radar applications are introduced in this proposal. A competing process is to estimate the space-time channel filter at the receiver and to perform internal RAKE processing. Part of the proposal is to compare the detection (ROC) performance of conventional phase conjugation, improved phase conjugation, and internal RAKE processing for monostatic and bistatic operation. The proposal also considers other ways to maximize energy-on-target: (1) Coherent combining of echoes from a sequence of waveforms that have low mutual interference, (2) SAR processing, and (3) adaptive waveform design to maximize signal-to-interference ratio (SIR). Phase conjugation processing, internal RAKE processing, multi-echo coherent combining, SAR, and SIR maximization require waveforms with different properties. Hyperbolic frequency modulation (HFM), modified hyperbolic-congruence frequency-hop codes, and modified Welch-Costas frequency-hop codes are considered for the various tasks.