Microwave photonic radar for distance and velocity measurement based on optical mixing and compressive sensing.

We propose a microwave photonic compressive sensing radar for distance and velocity measurement. First, a de-chirped signal that carries distance or velocity information is extracted between the transmitted and received signals in the proposed system. Then it is mixed with a pseudo-random bit sequence in the optical domain using a Mach-Zehnder modulator. After that, the de-chirped signal can be acquired by a photodetector and an analog-to-digital converter (ADC) at a sub-Nyquist sampling rate. Finally, a reconstruction algorithm can be used to recover the de-chirped signal. In our test, the bandwidth of ADC can be shortened from 2 GHz to 500 MHz, leading to a compression factor of four. A series of frequencies from 1.043 GHz to 1.875 GHz can be compressed with a 500-MHz ADC and recovered using a reconstruction algorithm. For a moving target, the Doppler frequency shift can be calculated, and the direction of the moving target can be distinguished. The maximum relative error of distance measurement is 0.21%. The maximum relative error of velocity measurement is 2.6%. The signal-to-noise ratio can be developed from ∼15 to ∼30. This microwave photonic compressive sensing radar can achieve distance and velocity measurements using few samples. Also, it provides a large bandwidth of system operation and reduces data processing and storage pressure.