Photonic approach for simultaneous measurements of Doppler-frequency-shift and angle-of-arrival of microwave signals

A photonic method used to simultaneously measure the Doppler-frequency-shift (DFS) and angle-of-arrival (AOA) of microwave signals is proposed and experimentally demonstrated. At the remote antenna unit (RAU), the local oscillator (LO) signal and two echo signals are applied to a phase modulator (PM) and a polarization-division-multiplexed Mach-Zehnder modulator (PDM-MZM), respectively. After transmission over a fiber link, the DFS and AOA parameters can be obtained by processing the two low-frequency electrical signals at the central office (CO). Experimental results show that the DFS between ± 100-kHz with < ± 5 × 10−3-Hz error and the AOA from 1.82° to 90° with <0.85° error at 10 GHz are obtained over a 10-km single mode fiber (SMF) transmission. Moreover, the DFS direction can also be distinguished by comparing the phase difference of two electrical signals.