Transmit Beamforming for Forward-Looking Space-Time Radars

Look-down airborne radars illuminate significant amounts of ground clutter, which due to the radar platform motion has a geometrically defined angle-Doppler characteristic. Space-time adaptive processing (STAP) is often employed at the receiver array to capitalise on the clutter angle-Doppler relationship and to detect targets, but there are significant problems with this approach in real-world scenarios, such as clutter non-homogeneity, which severely degrade STAP performance. In this chapter, the use of transmit beamforming is explored to alleviate some of these issues. The focus of the chapter will be the non-homogeneity of STAP training data caused by the forward-looking radar platform. In particular, the signal model for this scenario is developed and it is shown that there exist circumstances where transmit beamforming can significantly increase performance, particularly in range-ambiguous scenarios. Robust beamforming under uncertainties about the geometry will also be explored.