A Three-Port Polarization and Pattern Diversity Ring Antenna

In this letter, a novel design of a three-port antenna exhibiting pattern and polarization diversity characteristics is proposed. The radiating element of the proposed antenna comprises a ring loaded with periodical interdigital capacitors. The selective excitation of the three ports of the antenna enables omnidirectional and dual-polarized broadside radiation patterns in an overlapping bandwidth of 73 MHz (2.574<inline-formula><tex-math notation="LaTeX"> $-$</tex-math></inline-formula>2.647 GHz). The mutual coupling between any set of the two ports in the three-port antenna system is less than <inline-formula><tex-math notation="LaTeX">$-$</tex-math></inline-formula>20 dB. Six elements of the three-port ring antenna are arranged along the edges of a hexagon to generate 12 distinct beams (six dual-polarized broadside beams and six omnidirectional beams). Low mutual coupling and uncorrelated radiation patterns between the adjacent ports make the proposed three-port ring antenna a good candidate for use as an antenna element in massive multiple-input–multiple-output antenna systems for 5G applications.