A Novel Reflection-Mode Fabry-Perot Cavity Antenna With Broadband High Gain and Large Beam-Scanning Angle by Janus Partially Reflective Surface

Operational mechanism and design methodology of a novel reflection-mode (R-mode) Fabry-Perot cavity antenna (FPCA) are proposed in this article. Unlike common transmissive-mode (T-mode) FPCAs, the R-mode one places the feed antenna outside the cavity and introduces a Janus partially reflective surface (PRS), reducing the coupling between the feed and the FP cavity, while obtaining flexible displacement freedom of the feed to achieve a large beam scanning angle. The proposed R-mode FPCA employs a compact triple-layered Janus PRS, a simple ground plane, and a linearly polarized microstrip feed. The Janus PRS is applied to achieve bidirectional asymmetric transmission from the outside to the inside of the cavity to ensure the excitation efficiency and gain enhancement. In addition, a beam scanning model is proposed to obtain the spatial position of the feed and the maximum beam scanning angle under the specific antenna size. Finally, a proof-of-concept prototype is designed, fabricated, and measured at X-band. The measurement results agree well with the simulation, the 3 dB gain bandwidth of 19.7% is achieved. The peak gain in this range is 17.35 dBi and a large 3-D beam scanning range of [-35°, 35°] is also obtained.