A Photonic approach for Doppler-frequency-shift and angle-of-arrival measurement without direction ambiguity

A dual channel system based on a dual-parallel Mach–Zehnder modulator (DPMZM) is proposed for simultaneous measurement of angle of arrival (AOA) and Doppler frequency shift (DFS). The echo signals are received by two antennas and sent into two sub modulators (sub-MZMs) of the DPMZM respectively. The transmitted signal is fed into one of the sub-MZMs to act as a local oscillator signal. The upper and the lower sidebands of the output signal from the DPMZM are separated by a wavelength-division multiplexer (WDM) to form two channels. By measuring the power of the beating signal of the two channels, the AOA can be measured and the phase measurement error is less than 3.4° in the range of about 300° (The AOA is measured from ±10° to ±90°). Moreover, the system can measure DFS with the measurement error less than 0.07 Hz and determine the DFS direction by comparing the phase relationship between the two channels. The system structure is simple and compact, which is a simple and effective solution for modern radar and electronic warfare receiver.