Simultaneous Measurement of Doppler-Frequency-Shift and Angle-of-Arrival of Microwave Signals for Automotive Radars

A photonics-based scheme to simultaneously measure the Doppler-frequency-shift (DFS) and angle-of-arrival (AOA) of microwave signals for automotive radars is proposed in this paper. In the proposed system, an optical carrier is split into two branches. In one branch, a Mach-Zehnder modulator (MZM) is used to carry a transmitted signal, and in the other branch, a polarization-division-multiplexed MZM (PDM-MZM) is employed to imprint two echo signals. An optical filter is inserted in each branch to select one of the 1
^st
-order sidebands, and the chosen sidebands are then sent to a dual-polarization 90-degree optical hybrid. By processing the low-frequency signals from the two orthogonal outputs of the optical hybrid, DFS (with direction identification) and AOA can be simultaneously obtained. An experiment is carried out. The DFS measurement within ±100 kHz with a measurement error of ± 2.5 Hz and the AOA measurement from 27.25° to 90° with less than ±2.3° error are realized.