Range Enhancement and Passive Beamforming of a 24-GHz Object Detection Radar Using Partially Reflective Surfaces

This paper presents two partially reflective surface (PRS)-based techniques to enhance the performance of a 24-GHz object detection radar system. The first technique employs a flat PRS superstrate to increase antenna gain and thereby extend the detection range, while the second utilizes an inclined PRS structure to achieve passive beamforming and directional control. The conventional radar module consists of a 1 × 4 transmit array and two 1 × 4 receive arrays implemented on the opposite side of the PCB from the RF circuitry. Although increasing the number of antenna elements is an effective way to improve antenna gain and detection range, such an approach inevitably enlarges the antenna area and increases system complexity. In contrast, the proposed PRS-based structures enhance the effective aperture efficiency without expanding the planar dimensions of the antenna. The flat PRS configuration improves the antenna gain by approximately 5.8 dB (4.3 dB in Tx and 1.5 dB in Rx), which corresponds to a theoretical detection range extension of approximately 40% according to the radar range equation. Furthermore, the inclined PRS introduces a spatial phase variation across the aperture, resulting in passive beam steering of approximately −10 degrees while preserving the gain enhancement effect. Prototypes of both configurations were fabricated, and the measured results show good agreement with full-wave simulation data. These techniques provide compact and low-complexity solutions for extending detection range and enabling directional sensing in 24-GHz object detection radar applications.