Characteristic-Mode-Based Design of Planar In-Band Full-Duplex Antennas

Abstract

In-band full-duplex radios demand simultaneous transmit and receive (STAR) antennas with high isolation, compact and ultra-low profiles, and simple feed networks. Current state-of-the-art designs rarely meet all of these requirements at the same time. In this paper, we present a characteristic-modebased design approach to achieve high isolation using compact fully-planar STAR antennas with a simple feed structure. The proposed method utilizes two characteristic modes of a conducting object as transmit and receive chains to achieve high isolation without a complicated self-interference cancellation circuit. The design example in this work is fully-planar, and it has a physical height of 1.6 mm. The measured-10 dB overlapped |S11| and |S22| fractional bandwidth of this STAR antenna is 2.5% and the measured isolation between the transmit and receive ports is greater than 30 dB over the entire frequency band of operation.