LAUSR

A microwave photonic frequency and angle of arrival (AOA) measurement scheme, which overcomes the issue of limited extendibility in many reported structures, at the same time, offers the advantage of simplicity, is presented. It is based on a series connection of a parallel optical modulator with a pair of phase modulators, optical bandpass filters and photodetectors. Two low-frequency waveforms are generated after photodetection. The system input RF signal frequency and AOA can be determined by measuring the time difference between a reference point and the midpoint of the waveforms. Unlike most reported photonics-based frequency and AOA measurement systems, here the RF signal received by each antenna element is applied to a separate phase modulator. This enables the structure to be extended with minimal increase in complexity, making it suitable for use in a direction finding system with multiple antenna elements spaced far apart, thereby improving AOA measurement accuracy. Frequency measurement accuracy can also be improved, without reducing the measurement range, by increasing the number of signal paths with different path lengths. A proof-of-concept experiment has been set up to demonstrate the proposed frequency and AOA measurement scheme. Experimental results demonstrate that the proposed structure can determine an RF signal AOA in the range of -75° to 75° with errors of less than ±1.4° and an RF signal frequency in the range of 4 to 20 GHz with errors of less than ±80 MHz, based on the waveforms generated by the system. Frequency measurement of multiple RF pulsed signals with different pulse widths and frequencies is also demonstrated.