Millimeter-Wave ±45° Dual Linearly Polarized End-Fire Phased Array Antenna for 5G/B5G Mobile Terminals

In this article, a millimeter-wave (mmWave) endfire phased array antenna with ±45° linear polarizations is proposed for fifth generation (5G)/B5G mobile communications. The proposed antenna achieves ±45° polarizations by utilizing a modified substrate integrated waveguide (SIW) slot polarizer. The polarizer generates dual orthogonal modes with equal amplitudes and a 0°/180° phase difference, thereby yielding
$+ 45^{\circ }/- 45^{\circ }$
-polarization radiated waves in the far field. In a practical metal-framed mobile phone environment, the ±45 polarizations are verified to provide more balanced radiation patterns and, consequently, a higher polarization-multiple input multiple output (MIMO) efficiency. A prototype of the proposed 1
$\times $
4 array is fabricated and measured, achieving a −10 dB impedance bandwidth of 23.4–30.0 GHz (covers 5G band of n257/n258), with an isolation better than 15.6 dB and a realized gain above 8.9 dBi in the operating bandwidth. A peak gain of 11.4 dBi and a 3 dB scanning range of 87° can be observed at 27.0 GHz. Furthermore, the prototype is characterized on a metal-framed mobile phone platform, experimentally demonstrating its superiority to conventional vertical/horizontal polarized (V-/H-pol) arrays. The validated advantages of the balanced radiation patterns and robust impedance matching make the proposed ±45°-polarization endfire antenna array a promising candidate for mobile terminals in the era of 5G/B5G.