A Tripolarized Antenna With Ultrawide Operational Bandwidth

In multiscattering environment, the channel capacity can be enhanced by employing dual-polarized antennas, and more significantly, using tripolarized antennas. Aiming at providing a wide coverage of both existing wireless communication systems and the new 5G sub-6 GHz band, this article presents a compact ultrawideband tripolarized antenna. The proposed design consists of a monopole-equivalent structure for vertically linearly polarized (LP) omnidirectional radiation and two orthogonal stepped dipoles for ±45° LP broadside radiation. Several important design features are proposed and implemented. The dipoles act as parasitic elements for the monopole structure, which broadens the monopole bandwidth and reduces the mutual coupling. Furthermore, the port isolation is improved by inserting two metallic posts between the crossed dipoles and the ground plane. The measured results indicate that the fabricated prototype achieves an overlapped bandwidth of 84.73% (1.68-4.15 GHz) for <; -10 dB reflection coefficient and coupling value of <; -30 dB among all ports. Tripolarized radiation is verified with pattern measurement, showing peak realized gains of 8.4 and 9.4 dBi in monopole and two broadside modes, respectively.