Microwave Omnidirectional Angle-of-Arrival Measurement based on an Optical Ten-Port Receiver

Abstract

A photonics-based scheme to measure microwave omnidirectional angle-of-arrival (AOA) is proposed. In the proposed system, an optical carrier is split into two branches. In one branch, the optical carrier is frequency-shifted by an acousto-optic modulator (AOM) and led to a Mach-Zehnder modulator (MZM) which is modulated by an echo signal from an antenna. In the other branch, a polarization-division-multiplexed MZM (PDM-MZM) is used to imprint two different echo signals received by another two antennas, respectively. Then, an optical bandpass filter is connected after each modulator to select one of the 1st-order sidebands. The selected sidebands are sent to an optical ten-port receiver, which is consisted of a dual-polarization 90-degree optical hybrid and four balanced photodetectors (BPDs). After processing the low-frequency signals from the orthogonal outputs of the ten-port optical receiver, the azimuth and altitude AOA of the received RF signal could be simultaneously obtained. In a proof-of-concept experiment, the measurement error of the altitude AOA is less than 1.63 within the angular range of -48.08~56.43, and the measurement error of the azimuth AOA is smaller than 3.09 when the angular range is from -68.35 to 64.65.