A High-Aperture-Efficiency Fabry-Perot Antenna with Broadband Out-of-Band RCS Reduction Enabled by a Partially Reflective Absorptive Frequency-Selective Surface.

A high-aperture-efficiency Fabry-Perot (FP) antenna with broadband out-of-band radar cross-section (RCS) reduction enabled by a partially reflective absorptive frequency-selective surface (PRAFSS) is proposed. Unlike conventional absorptive frequency-selective surfaces that emphasize high in-band transmission, the PRAFSS is designed specifically for FP cavity operation. It provides controlled reflection and transmission near 1 GHz to sustain cavity resonance, while providing broadband absorption at higher frequencies for out-of-band scattering suppression. A prototype is designed, fabricated, and measured. The measured -10 dB impedance bandwidth is 965-1009 MHz (4.46%), and the measured gain reaches approximately 13.0 dBi near 985 MHz, with a gain enhancement greater than 2.2 dB relative to the reference antenna. Using the measured gain and the exact 416 mm × 416 mm physical aperture, the measured gain-based aperture efficiency is approximately 85.1%. Full-wave far-field simulations predict a continuous 10 dB monostatic RCS reduction band of 3.05-6.47 GHz. The finite-range measurement shows a consistent reference-normalized backscattering reduction band of 3.15-6.32 GHz. The results demonstrate a cavity-oriented design strategy in which high aperture utilization in the antenna operating band and broadband out-of-band scattering suppression are implemented by different electromagnetic responses of the same PRAFSS.