Simple photonics-based angle of arrival and Doppler frequency shift measurement system for long baseline antennas

Using photonics to measure the characteristics of an RF signal has a number of advantages compared to electronics. As a result, many photonics-based RF signal measurement systems have been reported. However, none of them can simultaneously measure an RF signal angle-of-arrival (AOA) and Doppler frequency shift (DFS) while having a simple and low-cost structure that is suitable for use in a long baseline antenna array. This paper presents a microwave photonic system to fill this technology gap. Additionally, the system is designed to have a robust performance, which is needed for practical applications. Measured results demonstrate simultaneous AOA and DFS measurement using the phase difference and the frequency of two low-frequency components generated by the system. The AOA and DFS measurement accuracy are within ±1° over the 0° to 81.5° AOA measurement range and within ±0.05 Hz over the ±50 kHz DFS measurement range. Results also show the system exhibits a stable performance with less than ±0.4° and ±0.02 Hz change in the measured AOA and DFS respectively, over an hour measurement period.