Active Excitation Tuning for Simultaneous Transmit and Receive Antennas

We present an actively tuned balun to enable Simultaneous Transmit and Receive (STAR) antennas to achieve greater isolation. Specifically, for the first time, we propose placing an active chip into the balun feed to control the amplitude and phase of the current density. Nearly perfect balance of the feed currents enables STAR antennas to maintain strong isolation despite fabrication imperfections and unpredictable environmental reflections. Measurements demonstrate 42 dB isolation across a 250 MHz bandwidth, representing an 11 dB boost. This is the best reported transmit-receive isolation improvement to date. Notably, the balun was tuned across 1.68-1.93 GHz. A prototype was fabricated and measurements show good comparison with simulation.