Photonic-Assisted Leakage Cancellation for Wideband Frequency Modulation Continuous-Wave Radar Transceiver

Frequency modulated continuous-wave (FMCW) radar systems suffer from permanent leakage from the transmitted signal into the receiver, which will reduce the dynamic range of the system and degrade the receiver sensitivity. Herein, a photonic-assisted leakage cancellation method for a wideband FMCW radar transceiver is proposed and experimentally demonstrated. At the remote antenna unit (RAU), a local oscillator (LO) signal, and a leakage signal are converted to optical signals with orthogonally polarization states by using a polarization-division-multiplexed Mach-Zehnder modulator (PDM-MZM). After the transmission of 10 km single mode fiber (SMF), the leakage signal is cancelled by using a variable optical attenuator (VOA), a variable optical delay line (VODL), and a balanced photodetector (BPD) at central office (CO). Compared with other analog cancellation methods, the proposed one has wider sweeping bandwidth and simpler structure. In the experiment, the LO signal and leakage signal are emulated by using an arbitrary waveform generator (AWG), a power divider, and two different length radio frequency lines. Then, experimental results show that a leakage cancellation depth of 17.5 dB at the carrier frequency of 15 GHz with a sweeping rate of 2 GHz/4 us is achieved.