As one of the mainstream direction finding schemes, correlative interferometer has many extraordinary advantages, such as low complexity computation, high accuracy, strong anti-interference etc. Besides, the uniform circular array can measure the azimuth angle and elevation angle simultaneously, and has the advantages of uniform direction finding accuracy and compact structure. Motivated by the above, this paper investigates the correlative interferometer direction finding using a uniform circular array. Since traditional electrical phase detectors are faced with some bottlenecks, such as bandwidth limitation, low frequency, electromagnetic interference etc., a photonic phase detector scheme has been presented to measure the phase difference. A dual-parallel Mach-Zehnder modulator (DPMZM) is adopted to construct an optical parallel interference structure which can estimate the phase differences by optical power measurement. The phase shift in DPMZM can be set to 0° and 180° by adjusting the DC bias. Then, the power of the output optical signal can be measured in both two cases. Besides, a Phase difference mapping function based on the ratio of optical power measurements has been proposed to improve the resolution of the power measurement and the estimation accuracy of the phase difference. Finally, the availability of the proposed scheme is investigated via experiments which shows that measurement error of phase difference is less than ±1° from 0° to 360° and the angle-of-arrival estimation accuracy is less than 1.0082°.

A novel high-accuracy microwave frequency measurement based on dual coherent optical frequency combs and stimulated Brillouin scattering was investigated. The unknown microwave signal and the sweep signal were modulated by two dual parallel Mach-Zehnder modulators as the signal optical and the pump signal which were lunched into the dispersion shift fiber. Using dual optical frequency combs and the sweep signal with shifted frequencies, the proposed measurement system could realize the wave-division and time-division multiplexing simultaneously. At the same time, the action of dual optical frequency combs and stimulated Brillouin scattering brought the system a series of stimulated Brillouin scattering. The frequency of the unknown signal was estimated by measuring the output optical power of the multiple channels. Furthermore, in order to improve the frequency measurement accuracy, the measured optical power values were employed to generate an amplitude comparison function which can be utilized for error correction. The effectiveness of the proposed scheme is verified via numerical simulations with a measurement error at ±2.5 MHz.