Hybrid Filters for Delay-Doppler Resolution Enhancement in Chirp Radar Systems.

We propose a chirp-hybrid filter system for Linear frequency modulated (LFM) radar systems. LFM chirp waveforms, which in general have good delay-Doppler resolution, are one of the most widely used classes of waveforms. However, LFM chirp radars have poor delay-Doppler resolution along the delay-Doppler (τ,ν) ridge ν = ατ of the ambiguity function, where α is the LFM index. In order to solve the poor ridge resolution problem in chirp radars, we introduce a chirp-hybrid filtering system, which consists of a matched filter and a mismatched filter. The mismatched filter design is simply a chirp waveform with a chirp-rate differing from the transmitted waveform, along with multiplication by a phase tuning waveform for each (τ,ν) grid point to be evaluated in the delay-Doppler filter bank. The proposed chirp hybrid filter system shows outstanding chirp ridge resolution compared to the poor ridge resolution of the traditional chirp matched filter system. Therefore, the chirphybrid filter improves delay-Doppler resolution and discrimination. Furthermore, the chirp hybrid filter can be easily and practically implemented in the traditional chirp matched filter systems with little increase in system complexity.