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 degrees 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.