MZM-Based FMCW Radar Receiver for Multi-Target Detection

Linear frequency modulated continuous wave (LFMCW)-based radar systems have gained significant popularity in a wide range of applications including sensing, automotive, and communication systems. LFMCW radars are preferred for their high time-bandwidth product, and inbuilt pulse-compression capability, yielding longer range detection with excellent range resolution [1]. FMCW radar operates on the fundamental idea of assessing the temporal disparity between the transmitted (tx_chirp) and the received (rx_chirp) waveform. The mixing of these waveforms results into a beat frequency (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta f$</tex>), which is subsequently utilized to determine the range and velocity of the target. Most photonics-based radar receiver systems employ electro-optic modulators (EOMs) with optical filters [2] to select the transmitted and received waveform for mixing, limiting the system's ability to adapt to different frequencies, along-with additional losses, potentially affecting the overall sensitivity and efficiency of the system. Some photonic radar receivers also use dual-drive Mach-Zehnder modulator (MZM) [3] for feeding both the transmitted and reflected waveform simultaneously necessitating the requirement of an additional electrical reference path. In this paper, we have achieved the photonic de-chirping through the received waveform that has both the coupled chirp (ref_chirp) and the received chirp (rx_chirp) component for multi-target detection, which essentially removes the requirement for optical filters, or using dual-port RF modulators for feeding the transmitted and received waveforms on the same EOM, thereby enhancing the system's performance.