Beamscanning Directivity Enhancement Based on Strong Interelement Mutual Coupling in Unequally Spaced Linear Arrays

Inspired by the 100-year-old Yagi-Uda antenna, the beamscanning directivity enhancement based on the strong interelement mutual coupling is proposed, explained, and verified in unequally spaced arrays with fixed configurations. First, the Y-port characteristic model analysis is employed over ideal array models to investigate the effect of strong interelement mutual coupling on beamscanning directivities. Then, a 3.5-wavelength array of 1x8 dipoles with varying spacings is designed for verification. The time reversal (TR) synthesis is introduced as a noniteration way to determine the optimal excitation with mutual coupling consideration for arbitrary array arrangements. The proposed unequal array enhances H-plane beamscanning directivities and realized gains with fixed array length and constant element number, achieving the defined superdirectivity ratio over unity. The angular and frequency ranges for enhancing beamscanning directivity of the proposed unequal array are also investigated. Diverse optimal arrangements are obtained for beamscaning from broadside to end-fire direction with the defined superdirectivity ratio from 1.1 to 3.5. The final experimental verification agrees with the simulated results. This work reveals that the strong interelement mutual coupling makes unequally spaced arrangements an effective way to enhance beamscanning directivity over fixed configurations, illustrating its potential for satellite communications and next-generation base stations.