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

This communication describes a compact four-element wide-angle scanning millimeter-wave (mm-wave) array for mobile phones. The wide-angle scanning array with four elements is achieved with a small element spacing of
$0.3\lambda _{0}$
. Two critical difficulties for the compact array with
$0.3\lambda _{0}$
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 (SPA) element working at 25.5–27.5 GHz is designed. The coupled shorted structure and coupled feeding structure of the element are designed to reduce the H-plane cross-polarization level (XPL) which is a key drawback of quarter-wavelength SPA. For the mutual coupling of the four-element array with
$0.3\lambda _{0}$
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
$1.14\times 0.3\lambda _{0}$
, 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 of less than 1.3 dB, a good sidelobe level (SLL), and an acceptable XPL. The proposed mm-wave array with the superior performance of small array size and wide beam scanning is promising for modern mobile phones.