ABSTRACT
This chapter considers a number of beamforming concepts and issues that arise in beamforming for through-the-wall radar imaging (TWRI) applications. The notion of the point spread function (PSF) as a standard measure of beamforming performance is presented, with specific emphasis on the PSF characteristics that result from the use of ultra-wideband waveforms. For the purposes of wideband beamforming, implementation options include beamforming-on-transmit and/or beamforming-on-receive. Specifically, the PSF mainlobe angular width is a measure of achievable angular resolution, the location and level of the PSF grating lobes determine angular ambiguity regions, and the PSF sidelobe levels indicate the capability of the beamformer to distinguish weaker scatterers in the proximity of stronger ones. The effect of a homogeneous wall on the PSF is examined analytically, where the wall is modelled as a single dielectric slab. The chapter discusses and compares a few different algorithms, including representative nonadaptive time-domain and frequency-domain algorithms, as well as a data-adaptive algorithm.
