Compact Millimeter-Wave Array With Wide-Angle Scanning for Mobile Phones

Abstract

This paper describes a compact four-element wide-angle scanning millimeter-wave array for mobile phones. The wide-angle scanning array with four elements is achieved with a small element spacing of 0.3λ0. Two critical difficulties for the compact array with 0.3λ0 spacing are the realization of the small element and the mutual coupling reduction between each element. For the small antenna element, a modified quarter-wavelength shorted patch antenna element working at the 25.5-27.5 GHz is designed. The coupled shorted structure and coupled feeding structure of the element is designed to reduce the H-plane cross-polarization level (XPL) which is a key drawback of quarter-wavelength shorted patch antenna. For the mutual coupling of the four-element array with 0.3λ0 spacing, three compact neutralization lines (NLs) are applied to reduce the mutual coupling to better than -15 dB. Finally, the proposed compact four-element array only occupies a small size of 1.14λ0 × 0.3λ0, which is the smallest mm-wave four-element array in the open literature. Also, the proposed array can scan from -60° to 60° with a peak gain of 9 dBi, a gain fluctuation less than 1.3 dB, a good sidelobe level, and an acceptable cross-polarization level. The proposed mm-wave array with the superior performance of a small array size and wide beam scanning is promising for modern mobile phones.