Microwave photonic direction finding with miniaturized antenna arrays: overcoming spatial constraints

In phase interferometer direction finding methods, the angle of arrival (AOA) is calculated by measuring the phase difference generated by the propagation of microwave signals between antenna array elements. In the direction finding technique based on the power-phase mapping relationship of microwave photons, there exists a mapping relationship between the power of the output optical sidebands and the phase difference, allowing the AOAto be obtained by measuring the power of the carrier waveform or sidebands. To address the technical challenges of small antenna array spacing, this work proposes a novel approach where it greatly improves direction finding accuracy. The two beams of optical carriers carry the differential-mode component and the common-mode component of the phase difference of the microwave signals, respectively, i.e.. After they are converted to electrical signals by the PD respectively, the power ratio (PR) of the two electrical signals is calculated. PR exhibits a mapping relationship with the AOA ,thus it can be derived by calculating the angle of arrival. Based on this method, MATLAB simulation software is employed to investigate antenna array spacings of λ/8, λ/12, λ/16, λ/20, and λ/50, where λ is the wavelength of the microwave signals. The simulated direction finding accuracies are ±0.42°, ±0.63°, ±0.83°, ±1.1°, and ±2°, respectively. The simulation results demonstrate that the proposed microwave photon direction finding system can meet the demand for high-precision direction finding with small antenna array element spacing.