This paper presents a continuous frequency tuning Fabry–Perot Cavity (FPC) antenna of which the operating frequency can be varied from 4.87 to 5.84 GHz (18.1%). The cavity of the proposed antenna is excited by a double-layer antenna structure, which is made up of a main square patch and a parasitic one. The superstrate is a frequency-selective surface, consisting of 6 × 6 square-patch-type unit cells. The frequency tuning property is realized by employing 48 phase-changing elements placed around the main patch, which forms a reconfigurable high impedance surface (HIS). By controlling the biasing voltages of the varactors inserted in the HIS element, its capacitances and reflection phases can be varied continuously, which leads to a variation of the operating frequency. An antenna prototype has been fabricated and measured for validation. The measured results are in good agreement with the simulated ones. In the frequency tuning range, the measured realized gains have a smaller variation from 10.2 to 14.1 dBi compared with other reported frequency tuning FPC antennas.
