A Folded Fabry–Perot Antenna With Low Profile

This letter proposes a novel folded Fabry-Perot antenna (FFPA) architecture for profile reduction. The architecture uniquely combines an orthogonally polarized conversion reflective surface (OPCRS) at the bottom layer with a polarization-selective partially reflective surface (PSPRS) at the top layer, creating two additional transmission paths to reduce profile height while adding two adjustable reflection phase parameters. Unlike most existing low-profile Fabry-Perot antennas (FPAs), which rely on either a partially reflective surface (PRS) or a ground with specific low-reflection phase characteristics and thus face significant design complexity, the proposed FFPA eliminates these constraints and simplifies the design process. Theoretical derivations confirm that FFPAs achieve high gain with a lower profile than conventional Fabry-Perots (CFPAs) under identical PSPRS conditions, regardless of the reflection phase characteristics of the PSPRS or OPCRS. A prototype FFPA exhibits a 16.9-dBi gain comparable to that of CFPA at 73.24% (0.3755λ) of the CFPA's profile. Moreover, leveraging the OPCRS's negative reflection phase, it also achieves a 12.1-dBi gain at a mere 17.86% (0.0915λ) of the CFPA's profile. These results validate the FFPA's low-profile characteristics and design flexibility, highlighting its significant potential for multifunctional, low-profile FPA applications.