Application of digital beamforming for look-down, clutter limited, MTI radar-with specific application to space based radar

For a look-down MTI radar to effectively detect moving targets, Doppler clutter must be suppressed. Where the target Doppler is within the mainbeam clutter, Displaced Phase Center Antenna (DPCA) or Space-Time Adaptive Processing (STAP) methods must be used. Even with these clutter suppression techniques, as grazing angles increase, the clutter power return increases faster than target power. This tends to severely limit the radar performance, and adding power doesn´t help much since clutter power will increase as signal power increases. Using multiple beams (n) at less power (1/n) can enable the effective use of additional transmit power and increase system area coverage rates, with constant performance. Specific application of this technique to an SBR will be analyzed. A simple example to illustrate the concept is a single radar with two 1/2 power beams. To keep signal strength comparable to the single beam full-power case, 2× dwell is needed, but as dwell times increase, the range/doppler cell size decreases by 1/2, decreasing clutter power by 1/2, so S/C actually improves, for each beam. Therefore less than 2× dwell is needed to maintain a constant S/I for each 1/2 power beam. So area coverage rate will increase since spot area increases by 2× and dwell time increases by less than 2×