A Compact Wideband Millimeter-Wave Polarization-Reconfigurable Antenna Array

This letter presents a wideband polarization-reconfigurable millimeter-wave antenna array using a compact feed network. The proposed geometry employs a Y-shaped feedline with a pair of p-i-n diodes to demonstrate a switching operation among three distinct polarizations: left-handed circular polarization (LHCP), right-handed circular polarization (RHCP), and linear polarization (LP). Two similar radiating segments, each comprising a pair of parasitic trapezoidal patches and three suspended metallic vias in a multilayer design, are excited through an aperture coupling technique. By careful optimization, the structure achieves the LHCP operation with a 3 dB axial ratio bandwidth (ARBW) of 24.0% and an impedance bandwidth (|S₁₁| < −10 dB) of 30.3%, the RHCP operation with corresponding parameters as 21.7% and 24.0%, and the LP response with an impedance bandwidth of 27.45%, as well as attains a good peak gain of 6.7 ± 1.0 dBic/dBi for all states in the broadside direction. To further enhance the performance, an antenna array with 2 × 2 elements is developed with an innovative feed network, showing an ARBW of 19.61% and 23.87% for LHCP and RHCP radiation, respectively, and a significant gain enhancement of 11.7 ± 1.0 dBic/dBi. The geometries have been fabricated and measured, showing satisfactory resemblance between the responses.