Dual‐polarized stacked microstrip antenna with trident‐shaped baluns for MIMO array development

Abstract

Owing to the high cross-polarization discrimination (XPD) and high isolation characteristics, differential excitation is often employed in dual-polarized microstrip antennas. However, the number of excitation ports will be doubled, and the power dividers in the differential circuit will introduce additional loss, the differential excitation scheme is thus not suitable for dual-polarized large-scale MIMO antenna arrays. In this work, a novel dual-polarized stacked microstrip antenna with trident-shaped baluns is proposed for base station MIMO array development. The trident-shaped balun is proposed to replace the traditional differential excitation structures, while keeping the merits of high XPD and high isolation. The proposed antenna operates in the frequency band of 3.3-3.8 GHz. The profile height of the antenna is only 0.09λ0 (λ0 is the free-space wavelength at the central frequency), which is much lower than traditional base station antennas (0.25λ0) in the sub-6 GHz band. Moreover, a defective ground structure is implemented in a 2 × 2 MIMO antenna array to efficiently suppress the mutual coupling among antenna elements. Both simulated and measured results validate the design. Owing to its low-profile height and low mutual coupling characteristic, the proposed design is a good candidate for sub-6 GHz band base station MIMO array developments.