Quad-Band Diplexing Filtennas with Reciprocal/Orthogonal Feeding Types for Radiation Pattern Diversity

In this article, novel quad-channel diplexing antennas based on capacitor-loaded co-directional split ring resonators (CDSRRs) are proposed. For this purpose, a wideband circular monopole antenna is firstly designed to cover the frequency range from 3 to 6 GHz, where the channels will be located. Four pairs of CDSRRs are coupled to the feeding lines from two sides of the circular patch to obtain highly selective four channels. Since a single CDSRR can create two resonant frequencies, all channels consist of two reflection zeros. For experimental demonstration, two diplexing antennas having reciprocal (in-line) and orthogonal (perpendicular) port connections for variable radiation patterns were implemented and measured with the fair agreement with the predicted results. The center frequencies of the reciprocal/orthogonal diplexing antennas are almost the same and were measured at 3.3/3.35, 3.98/4.05, 4.67/4.8, and 5.72/5.76 GHz.