Abstract
A photonic-assisted scheme based on optical frequency shift heterodyne and low-frequency power mapping is proposed and experimentally demonstrated to measure the Doppler frequency shift (DFS) and Angle-of-arrival (AOA) of the microwave signals. In the proposed system, the optical signal is divided into two paths. The upper optical signal is injected into a dual-drive Mach-Zehnder modulator (DDMZM) and modulated by the two echo signals with a phase difference. The lower path optical signal is frequency-shifted by an acousto-optic modulator (AOM) and then modulated by the transmitted signal via a Mach-Zehnder modulator (MZM). After an optical filter, the two first-order sideband optical signals heterodyne in the photodetector. The DFS without direction ambiguity and AOA are mapped to the frequency shift and power of the low-frequency microwave signal. By adjusting the DC bias of the DDMZM, two power-phase mapping curves are obtained to eliminate phase ambiguity in AOA measurement. The measurement accuracy is enhanced by adjusting the identity of the two power mapping curves in different measurement ranges. A proof-of-concept experiment demonstrates a DFS measurement at 20 GHz with errors less than ± 8 Hz in the range of ±100 kHz and an AOA measurement from -62.5° to 62.5° with no more than ±2.5° errors.
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