Wideband Near-Field Correction of a Fabry–Perot Resonator Antenna

A systematic approach to correcting electric near-field phase and magnitude over a wideband for Fabry-Perot resonator antennas (FPRAs) is presented. Unlike all other unit-cell-based nearfield correction techniques for FPRAs, which merely focus on phase correction at a single frequency, this method delivers a compact nearfield correcting structure (NFCS) with a wide operational bandwidth of 40%. In this novel approach, a time-average Poynting vector in conjunction with a phase gradient analysis is utilized to suggest the initial configuration of the NFCS for wideband performance. A simulationdriven optimization algorithm is then implemented to find the thickness of each correcting region, defined by the gradient analysis, to complete the NFCS design. According to the predicted and measured results, the phase and magnitude distributions of the electric near field have been greatly improved, resulting in a high aperture efficiency of 70%. The antenna under NFCS loading has a peak measured directivity of 21.6 dB, a 3 dB directivity bandwidth of 41% and a 10 dB return loss bandwidth of 46%, which covers the directivity bandwidth. The diameter of the proposed NFCS is 3.8λ_0c, which is around half that of all the other unit-cell-based phase-correcting structures, where λ_0c is the free-space wavelength at the central frequency of the NFCS (13.09 GHz).