Contents I. Introduction
To accommodate an ever-increasing pool of competing wireless users, efficient use of spectrum is more important than ever. A myriad of multiple access schemes are well-established (e.g., FDMA, TDMA), but they rely on a limiting axiom: a system must transmit and receive on orthogonal channels. Recently, a number of researchers have challenged this principle, demonstrating systems capable of Simultaneous Transmit and Receive (STAR) [1], [2]. Such systems can transmit and receive signals on the same frequency band, at the same time, potentially doubling wireless link capacity. A key component of such a system is the antenna, which must provide sufficient transmit to receive isolation to prevent saturation of the receiver.
