A Double Layer Cross-Slot Aperture-Fed Millimeter-Wave Antenna Array With Wide Axial Ratio Bandwidth.

yThis letter presents a double-layer cross-slot aperture-fed antenna array with wide axial ratio bandwidth for 5G millimeter-wave applications. Each of the antenna elements comprises two parasitic trapezoid patches and three suspended metallic vias, which are excited through an aperture coupling technique with the help of a cross-slot geometry. Two circularly polarized (CP) resonances are produced by each antenna, yielding an overall wideband CP behavior upon optimization. Superior performances are thereby observed from the antenna element in terms of a wide 3-dB axial ratio bandwidth (ARBW) of 26.38%, a wide -10 dB impedance bandwidth > 31.40%, and a large gain (5.6 +/- 1.0 dBic) in the broadside direction. To further improve the characteristics, a 1 x 4 antenna array is devised using a corporate feed network, which exhibits an extensive ARBW of 30.34%, a broadband impedance bandwidth >33.33%, and an increased gain of 11.2 +/- 1.0 dBic. Both the single element and antenna array are fabricated, and their measured responses are in reasonable agreement with the simulated results.