Wideband Antenna Array for Simultaneous Transmit and Receive (STAR) Applications

Design and performance of a nonscanning antenna array with wideband simultaneous transmit and receive capability are discussed. The proposed configuration utilizes a four-arm spiral antenna as a unit cell to achieve high isolation between transmit (TX) and receive (RX) ports and decent far-field performance. It is shown that the analytically derived system isolation is theoretically infinite for symmetric array under ideal conditions. The proposed antenna is composed of seven four-arm spirals arranged in a hexagonal configuration. Each spiral has two arms for TX, and two arms for RX. Planar microstrip feeds are used to excite each two-arm spiral and eliminate the need for 180° hybrids. The spiral arms are resistively loaded to improve VSWR and axial ratio and reduce interaction with the ground plane. Isolation between the collocated TX and RX arrays > 27 dB, as well as VSWRs <; 2, sidelobe levels <; -10 dB, and good patterns for both arrays are measured over more than two-octave bandwidth.