A Low-Profile Dual-Band Dual-Polarized Quasi-Endfire Phased Array for mmWave 5G Smartphones

This paper presents a very low-profile ( $0.105\lambda _{0}$ at 28 GHz) dual-band dual-polarized millimeter-wave phased array for 5G smartphones. The array element is based on two distinct dual-band antennas to realize two orthogonal linear polarizations. A planar folded dipole with a parasitic strip is used to produce horizontally polarized radiation, and a novel hexagonal bridge antenna is devised to generate vertically polarized radiation while maintaining a very low profile. A prototype of a $1\times 4$ phased array is designed and implemented on a multilayer laminate using standard printed circuit board process. The real estate of the array is kept within $6.5\,\, \mathrm {mm}\times 23\,\, \mathrm {mm}\times 1.12\,\, \mathrm {mm}$ . For both polarizations, the −10 dB bandwidth covers 25.4–30.84 GHz and 38–40 GHz with peak gains of 11.31 and 11.93 dBi at two center frequencies, respectively. The overlapped 3 dB scan ranges between both polarizations are ±45° at 28 GHz and ±39° at 39 GHz. This work considers a number of important design challenges of implementing low-cost mmWave antennas in smartphones, providing a practical solution to mmWave 5G mobile devices.