Broadband Radar De-chirping Receiver Based on a Microwave Photonic I/Q Mixer

A broadband radar de-chirping receiver based on a microwave photonic in-phase and quadrature (I/Q) mixer is proposed to realize image-reject radar detection. The proposed radar receiver uses a microwave photonic I/Q mixer to implement de-chirping processing of the broadband radar echo, obtaining a pair of low-frequency I/Q signals with orthogonal phases. The microwave photonic I/Q mixer is built upon a cascaded modulation structure to accomplish electro-optical (EO) conversions of the radar echoes and the reference signals in the same optical channel containing modulators and fiber links. In this way, the phase unbalance issue between the I and Q channels is avoided and the phase stability of the radar receiver is enhanced. In the experiment, a radar de-chirping receiver is established and successfully implements de-chirping processing of broadband linearly frequency modulated (LFM) radar echoes with image-rejection ratio of more than 37 dB.