Multichannel microwave photonic based direction finding system

A new microwave photonic topology for RF signal direction finding is presented. It is based on a dual-parallel Mach Zehnder modulator (DPMZM) in series with an optical phase modulator (PM). The direction of an RF signal received by the antennas connected to an RF port of the DPMZM and the PM can be determined from the power ratio of two system output low frequency components, without the need to know the incoming RF signal amplitude in advance. The proposed structure is suitable for implementing a long baseline technique for direction finding and can be extended to have multiple antenna elements in remote locations. In addition to direction finding, the system also has the ability to measure an RF signal Doppler frequency shift to determine an object speed and moving direction when it is used in a radar receiver. Results obtained using the proposed structure demonstrate less than ±2.5° errors over a 3.2° to 81.5° angle of arrival measurement range for different RF signal modulation indexes of 0.02, 0.08 and 0.16. Doppler frequency shift measurement with less than 0.8 Hz errors is also demonstrated.