Simple Doppler Frequency Shift Measurement Scheme Based on Microwave Photonics

Based on the theory of microwave photonics, we propose a new scheme to measure the Doppler frequency shift (DFS) in a radar system. This scheme is a single-channel system based on dual-parallel Mach–Zehnder modulator (DPMZM). And the frequencies of the transmitted signal and the reference signal are added together to form a combined signal. Then we add the combined signal and the echo signal to the two sub-modulators (sub-MZMs) of DPMZM, respectively. By measuring the beat signal output by the photoelectric modulator (PD), the DFS can be measured, whose error is maintained at −0.8Hz to 0.8Hz. The DFS's direction is determined by comparing the frequencies of the obtained signal and the reference signal. The system has the advantages of wide operating frequency range, simple structure, low cost, and easy integration.