Performance analysis and feed location optimization for enhanced isolation and polarization control in dual differentially fed antennas

This paper presents an analysis of a low-profile dual differentially fed patch antenna, considering both differential impedance and pair-to-pair isolation, thereby mitigating the need for more complex feeding networks. A new relationship between differential pair-to-pair isolation at resonance versus feed location is revealed. This relation favors optimal pair-to-pair isolation over ideal impedance-matching conditions. The exciting port-to-patch center distance is shown to be significant in determining both the differential input impedance and pair-to-pair isolation. A differential pair-to-pair isolation greater than 38 dB is measured across the entire band from 9.17 GHz to 9.37 GHz. The polarization control of a dual, differentially fed antenna with full integration of off-the-shelf RF components is introduced. A cross-polarization (X-pol) ratio lower than -31 dB is achieved across the entire band for linear polarizations (LP) using RF baluns, while a left-hand circular polarization (LHCP) is achieved with an extra 90° hybrid coupler connected to the baluns. Despite the known poor isolation of the commercial hybrid coupler and its amplitude and phase imbalances, the achieved axial ratio (AR) is better than 1 dB across the entire band. • Investigate the effect of the feeding ports spacing (feed-center location) on the differential pair-to-pair isolation. • Identification of the optimal feed location that ensures the highest isolation performance. • Achievement of a high cross-polarization (X-Pol) ratio and low axial ratio (AR) across the entire operational bandwidth. • Comparison of E-field and surface current distributions in dual differential-fed vs. conventional two-port antennas. • Validation of classic single differential-fed closed-form model for applicability to proposed dual differential-fed antenna.