Microwave Photonic Joint Radar and Secure Communication via Radar Signal Masking

A microwave photonic system for joint radar and secure communication is proposed. Microwave photonic frequency multiplying and frequency conversion are simultaneously employed to shift the radar and communication signals to the same frequency band concurrently. The radar signal is designed to have a greater power to mask the communication signal, increasing the difficulty of signal interception and thus enhancing security. By employing dechirping at the radar receiver and self-interference cancellation (SIC) at the communication receiver, respectively, the radar function can be implemented and the communication signal can also be correctly demodulated after removing the radar masking. An experiment is performed. A 0.3-GHz bandwidth linearly frequency-modulated (LFM) signal is quadrupled and superimposed with two upconverted 0.5-Gbaud orthogonal frequency-division multiplexing (OFDM) signals. A communication data rate of 2 Gbit/s, a radar ranging measurement error of less than ±0.3 cm, and a radar inverse synthetic aperture radar (ISAR) imaging resolution of $12.5\times 10.2$ cm are achieved.