Photonic-Assisted Adaptive Wideband Self-Interference Cancellation Based on Self-Mixing for FMCW Radar

An adaptive photonic-assisted wideband self-interference cancellation (SIC) scheme based on self-mixing for frequency-modulated continuous-wave (FMCW) radar is proposed. The signals are modulated onto the optical carrier using a dual-polarization quadrature phase shift keying (DP-QPSK) modulator. After adjusting the delay and amplitude of the reference signal in the optical domain, the self-interference (SI) signal is eliminated through a balanced photodetector (BPD). The output signal from the BPD and the reference signal are mixed and then downconverted to zero intermediate frequency. By checking the delay difference between the signal of interest (SOI) and the SI signal, the two signals are distinguished. The Hooke-Jeeves (HJs) algorithm takes the power of the SI signal after self-mixing as the objective function, adaptively optimizing the delay and amplitude of the reference signal until the objective function is minimized. Experimental results show that the scheme can successfully recover the SOI, with the SI signal being eliminated more than 30 dB. The scheme achieved cancellation depths of 33.2 and 31.9 dB for broadband signals in Ku-band with bandwidths of 500 MHz and 1 GHz, respectively. Additionally, we demonstrated the cancellation of signals within the 4–40 GHz range, with a bandwidth of 100 MHz, achieving a cancellation depth >30 dB.