Angle-of-Arrival Measurement System Using Double RF Modulation Technique

A new technique for determining the angle of arrival (AoA) of an RF signal is presented. It is based on a cascaded modulator structure, where continuous wave light from an optical source is modulated by an incoming RF signal twice. The AoA of an RF signal can be determined by the system output RF signal power. The proposed structure is capable for measuring the AoA of both narrow and broadband RF signals. This overcomes the limitation in all previously reported photonics-based AoA measurement systems, which are applicable to either a single-frequency RF signal or a broadband RF signal. It also does not involve electrical components and high extinction ratio modulators, which are required in reported structures. Experimental results are presented that show an AoA measurement range of 0 degrees to over 65 degrees with errors of less than 1.9 degrees for a microwave signal at 2.65 and 12.62 GHz. Results also show that the system is capable to measure the AoA of a pseudorandom binary sequence signal at a microwave frequency.