Dual-band shared-aperture Fabry-Pérot cavity (DS-FPC) antennas with single-layer partially reflective surface (PRS) are inherently limited in the achievable frequency ratio. This paper analyzes such antennas to derive the feasible range of frequency ratio and thereafter proposes a dual-band shared-aperture antenna that can fill the frequency ratio gap. The proposed antenna integrates a short backfire antenna (SBA) for the low band (LB) and a Fabry-Pérot cavity (FPC) antenna for the high band (HB), utilizing a shared single-layer PRS and a parasitic element. In LB, using a parasitic element that is transparent for HB, the SBA works well despite its low profile. In HB, the FPC antenna works with the first-order FPC mode. A prototype working at 5.5GHz and 9GHz was fabricated and measured. The overall height of the antenna is 0.36 and 0.59 wavelength in LB and HB, respectively. The prototype achieves 7.3% and 6.7% of measured overlapping 10dB impedance bandwidth and 3dB realized gain bandwidth, as well as peak realized gains of 10.3 and 14.6dBi, in LB and HB, respectively.

A reconfigurable partially reflective surface (PRS) antenna can offer low-cost and low-complexity beam steering, traditionally implemented using a phased array with a bulky feeding network. This paper utilizes ray-tracing to prove analytically that an inductive nonuniform PRS facilitates larger beam deflection and lower sidelobe level (SLL) than a capacitive one, given the same reflection phase difference. With a suitable tradeoff in the beam deflection angle and gain variation between the reconfigurable states, an inductive reconfigurable PRS is designed for a ±13° steering range. To enhance the steering range with minimal complexity, two parasitic elements loaded with PIN diodes are added to the feeding source, resulting in the overall steering range of ±30°. The fabricated prototype verified that the pencil-shape beam can be steered towards 0º and ±30º with SLLs of less than -19dB at 5.5GHz. The antenna achieved peak realized gains of 9.5-10.4dBi for the three states with gain variation of less than 0.9dBi. The measured overlapped impedance band covers 5.41-5.63 GHz for all states.