Photonic generation of dual-band complementary linearly chirped microwave waveforms based on phase modulator

Abstract

A simple scheme to generate a dual-band complementary linearly chirped microwave waveform using a Mach–Zehnder modulator (MZM) paralleled with a phase modulator (PM) is proposed. In the scheme, a five-line optical frequency comb, generated by MZM, is combined with a phase modulated optical chirp waveform by a baseband parabolic signal or a single-chirp signal as two beams with inverse relative phases via a 2 × 2 optical coupler. After balanced detection with heterodyne beating, the dual-band complementary linearly chirped microwave waveform is generated for the two driving cases, and they demonstrate different enhanced performances. The dual-band complementary linearly chirped microwave waveforms with center frequency of 20 and 40 GHz are generated simultaneously for both cases by simulation. The generated two complementary linearly chirped waveforms with a baseband parabolic driving signal have a larger bandwidth of 7.6 GHz, corresponding to larger pulse compression ratios (PCRs) of 1462.86 and 1365.33, which could effectively improve the range Doppler resolution in modern radar systems, although their peak-to-sidelobe ratios (PSRs) are only 12.98 and 12.97 dB. Although for the case with a single-chirp driving signal, the PSRs of the two waveforms with a bandwidth of 4 GHz are higher, 13.66 and 13.67 dB, respectively, but with the PCRs of only 787.69 and 758.52, which is of practical significance for radar detection in weak targets and multitargets.