Structured de-chirp for compressive sampling of LFM waveforms

Stretch processing is often used by radar systems to capture LFM waveforms. Although stretch processing reduces sampling rate, it does so at the expense of increased data collection period. Therefore, the time-bandwidth product of the de-chirped waveform is approximately constant, and stretch processing cannot be considered a compressive technique. The sample rate of a stretch processor must match the bandwidth of the beat frequencies created in the de-chirp process. Uniform sampling at lower rates will cause range ambiguities without an anti-aliasing filter, but an anti-aliasing filter removes part of the range swath. We propose a hopping de-chirp signal (sensing matrix) that shifts regions of the range swath in and out of the anti-aliasing filter´s bandwidth. This hopping produces a unique time profile of beat frequencies for each range in the swath and enables compressive sampling without sacrificing range swath or resolution and without introducing ambiguities. After describing the hopping de-chirp technique, we analyze multichannel implementations where it is possible to use a different hopping sequence on each channel.