Millimeter-Wave Dual-Polarized Multibeam Endfire Antenna Array With a Small Ground Clearance

A dual-polarized multibeam endfire antenna array is presented for 5G millimeter-wave applications. The antenna element employs double-layer stack-up substrate integrated waveguides (SIWs) and stepped slot to serve as a polarizer. Dual-linear polarization can be generated when the two SIWs are fed with in-phase and out-of-phase signals. A resonated metallic loop and two pairs of bilateral connecting lines are loaded in front of the antenna aperture to improve impedance matching and enhance gains. The ground clearance is only 1.5 mm, thus is attractive to be applied for mobile terminals. A
$1 \times 4$
multibeam array is constructed to evaluate the beamforming capability. Butler matrix and 180° hybrid couplers are used to provide the required feeding signals. The measured bandwidth is larger than 10% for both polarizations, capable of covering n257 and n261 bands. The measured peak gains of vertical and horizontal polarizations are 9.38 and 9.51 dBi, with an overlapped 3 dB azimuthal range covering ±48°.