A Compact Three-Port Antenna With Enhanced Inter-Port Isolation for Polarization and Pattern Diversity

This paper presents a compact three-port antenna design suitable for use in mobile radio systems that require polarization and pattern diversity. The antenna design utilizes a shorted bow-tie patch split in half with an air gap and a top-loaded two-element monopole placed along the gap on a small common ground plane (
$0.37\lambda ^{2}$
) to achieve a compact form factor. The patch is excited by aperture coupling and probe feeding via two independent ports, producing two orthogonally polarized broadside patterns for polarization diversity. Meanwhile, the co-located monopole generates a vertically polarized omnidirectional pattern to provide pattern diversity. High inter-port isolation (> 25 dB) is achieved by incorporating simple decoupling structures shorted to the ground plane between the patch and the monopole. Measurements on the antenna prototype show that envelope correlation coefficients among the three different radiation patterns are lower than – 37 dB (or 0.0002) within the operating bandwidth, making this antenna a good candidate for diversity applications.