Group delay engineering using cascaded all pass filters for wideband chirp waveform generation

In this paper a second order all pass filter (APF) is designed and analyzed for its potential application for wideband chirp waveform generation. The group delay of a single stage APF varies with frequency within a narrow band and remains flat elsewhere. Furthermore, it has been found that the component values have a great role in the group delay response of the APF. A two stage cascaded second order APF is adopted to enhance the group delay over a wider band. Genetic algorithm is used to optimize the design parameters of the individual APF stages to obtain a smooth and monotonically increasing group delay response while ensuring good input return loss characteristics. This design approach can be used for generating wideband chirp waveforms that have potential applications in radar, sonar and imaging, delivering improved range resolution.