Active Retrodirective Rotman Lens Antenna for Wide-Angle RCS Enhancement

This paper presents measurement results and analysis of an innovative active retrodirective Rotman lens antenna architecture, designed to enhance the radar cross-section (RCS) for backscattering applications. Unlike conventional passive retrodirective systems, our design integrates custom-designed reflection amplifiers to significantly boost backscattered signal gain while maintaining low DC power consumption. A novel biasing technique enables independent phase and gain control of the amplifiers, ensuring a uniform array response and reducing DC power consumption by approximately 30%. Experimental monostatic RCS measurements at 5.15 GHz with a linearly polarized incident wave demonstrate a uniform RCS response over a ±40° scan angle. The integration of reflection amplifiers enhances backscattering, allowing the lens to maintain a consistent −0.5 dB RCS across the entire scan angle, which is 9 dB higher than the average RCS of a metal plate with the same effective aperture. The compact design (approximately $6\lambda \times 6\lambda $ ) and ultra-low power consumption (approximately 0.19 mW) make this system well-suited for low-power radar applications, such as mm-wave automotive radar sensors. These results confirm the feasibility of active-loaded phase conjugating systems for high-performance backscattering applications.