Compact two-port MIMO antenna dual-circularly polarized 28/38 GHz with polarization diversity for 5G and beyond millimeter-wave systems

Abstract

This paper presents a compact dual-band circularly polarized two-port MIMO antenna for millimeter-wave applications at 28 and 38 GHz. The single-element antenna occupies an ultra-small area of 8 mm × 16 mm and is fabricated on a Rogers RO3003 substrate (εr = 3, thickness = 0.25 mm). Circular polarization is achieved at both bands, with measured axial ratios of 1.4 dB at 28 GHz and 2.2 dB at 38 GHz, providing robustness against polarization mismatch. The antenna achieves peak realized gains of 7.5 dBi and 5.5 dBi at 28 GHz and 38 GHz, respectively. Experimental results show good impedance matching and radiation patterns in close agreement with simulations. Based on the validated single-element design, a two-port MIMO configuration is implemented, where one element generates RHCP and the other LHCP, enabling polarization diversity. The MIMO antenna exhibits low envelope correlation coefficient and high diversity gain. Owing to its compact size, dual-band circular polarization, and effective polarization-diverse MIMO performance, the proposed antenna is suitable for space-constrained 5G and future millimeter-wave wireless devices.