Photonic scheme for simultaneous Doppler frequency shift and two-dimensional angle of arrival measurement without direction ambiguity and power dependence

A photonic method for the simultaneous measurement of Doppler frequency shift (DFS) and two-dimensional angle of arrival (2-D AOA) without direction ambiguity, based on three parallel Mach-Zehnder modulators (MZMs), is proposed. In our scheme, three parallel MZMs are separately driven by the combination of echo and reference signals from the three non-collinear antennas to modulate the lightwave in carrier-suppressed double-sideband modulation (CS-DSB) pattern. The generated optical signals are detected by three identical low-speed photodetectors (PDs) in parallel to separately down-convert the echo signals to the intermediate frequency (IF) signals. The value and direction of the DFS can be deduced from the IF signals with the aid of the reference signals, and both azimuth and altitude AOAs without direction ambiguity are obtained by analyzing the phase difference between the IF signals. The simulation results show that the measurement error of the altitude AOA is less than 1.5° within the range of -85^∘ to +85^∘, and the azimuth AOA can be measured with an error of less than 5° within -83.51^∘ to 83.27°. Furthermore, the measured DFS has an error within 0.2 Hz for the 10 GHz echo signal. The proposed scheme can realize the simultaneous measurement of DFS and omnidirectional two-dimensional AOA with large bandwidth, and without power dependence on echo signals, and is expected to have broad application prospects in future microwave photonic radar systems.