A High-Isolation, Ultra-Wideband Simultaneous Transmit and Receive Antenna With Monopole-Like Radiation Characteristics

A high-isolation, ultra-wideband simultaneous transmit and receive (STAR) antenna with monopole-like radiation characteristics is presented. The proposed STAR antenna consists of a center-located monocone and a circular array of bent loops. The monocone and the array of loops are located in the near fields of each other and serve, respectively, as the transmit (TX) and receive (RX) antennas. To achieve omnidirectional, vertically polarized radiation patterns, the array factor of the bent loops is first examined. A circular top loading and four T-shaped parasitic elements are exploited to decrease the lowest frequency of operation of the antenna without increasing its occupied volume. Finally, based upon the analysis of the array factor, four directors are strategically mounted over the ground plane to enhance the omnidirectionality of the antenna in the azimuth plane. A prototype of the antenna operating in the UHF band is fabricated and measured. Experimental results demonstrate that the proposed STAR antenna achieves an isolation greater than 40 dB from 0.6 to 1.75 GHz (2.9:1 bandwidth). Furthermore, the STAR antenna is capable of maintaining consistent monopole-like radiation patterns and vertical polarization for both the TX and the RX channels across the entire band of operation.