Broadband Microstrip Slot Antenna With Triple-Polarized Characteristics

A single-layer wideband slot antenna with triple-polarized characteristics is proposed in this letter. One circular slot mode is excited by one microstrip/slotline with a λ/4 open stub. Then, two capacitive-coupled circular dipole modes are excited by adding curved micrsotrip-fed lines and circular radiating patches symmetrically in the center of the circular slots along the perpendicular direction. Thus, triple-polarized feature is achieved. The antenna parameters can be optimized for wide bandwidth as well as high port-to-port isolation and good cross polarization. The antenna is fabricated, and the measured results show that 25-dB port-to-port isolation and 20-dB cross-polarization level between each two polarizations of the three modes across the 10-dB return-loss impedance bandwidths of 46%, 49%, and 49%, respectively, are obtained. The compact structure with triple-polarized characteristics, high isolation, and low cross-polarization levels proves it a good candidate for base-station antenna applications.