Characterization of diversity approaches for LFM stretch-processed waveforms

Frequency diversity in linear frequency modulated (LFM) waveforms can introduce unintended range shifts among receive radars in a distributed environment. This can make it difficult to predict where interference will occur in those receive radars, particularly when multipath is considered. This paper introduces the concept of interference region in range-frequency space to characterize the interference levels at a receive radar caused by waveforms transmitted from different radars in a distributed architecture. Linear frequency modulated (LFM) stretch-processed waveforms provide wide bandwidth and high range resolution while imposing only modest demands on the digital processing capabilities of a radar system. For this reason they are the waveform family of choice for many current wideband radar systems, including synthetic aperture radar (SAR) systems. However, LFM waveforms do not easily lend themselves to applications that require orthogonality, such as distributed radar architectures. The widespread use of these waveforms and the processing advantages they provide make it worthwhile to examine schemes for their use in a distributed environment. The paper uses interference region analysis to assess the effectiveness of frequency diversity, upchirp-downchirp diversity and chirp slope mismatch using LFM stretch-processed waveforms in a distributed environment.