Dual-Functional Microwave Photonic System for Target Detection and Frequency Measurement

A microwave photonic (MWP) system that integrates two functions of target detection and frequency measurement is proposed and demonstrated. The target detection function is achieved using an MWP radar, in which an optically generated linearly frequency-modulated (LFM) microwave waveform with complementary chirps is generated and transmitted, and an echo scattered from a moving target is received, which is mixed with the transmitted waveform to obtain a de-chirped microwave waveform with two different frequencies. The distance and radial velocity of the moving target are measured simultaneously. For frequency measurement, an unknown signal under test (SUT) received at the radar receiver is modulated on an optical carrier, which is combined with a frequency-sweeping light (FSL) and applied to a photodetector (PD). After being filtered by a narrowband bandpass filter (BPF), short pulses are generated. The frequency of the SUT is obtained by measuring the time delay difference between pulses. The operation of the proposed dual-functional system is evaluated experimentally. High precision distance and radial velocity measurements are achieved with mean absolute errors (MAEs) of 2.58 cm and 3.08 cm/s, respectively. The frequency measurement capabilities for single-tone, multitone, and broadband signals are also evaluated with an MAE of 34.22 MHz and a resolution of 40 MHz.