Differential Fed Antenna with High Self-Interference Cancellation for In-Band Full-Duplex Communication System

This paper presents a novel design of high self-interference cancellation (SIC) technique for microstrip antennas. The proposed antenna consists of two closely-spaced orthogonal antennas with differential feeding as SIC circuit so as to achieve high interport isolation between the transmitter and receiver. In order to achieve high RF leakage cancellation, a novel differential feeding network (DFN) is also proposed in this paper, which provides amplitude and out-of-phase imbalances within 0.12 ± 0.03dB and -180 ± 1°, respectively, for the bandwidth of 500 MHz at a center frequency of 2.50 GHz. General analytical design equations are derived for achieving high SIC over the wide bandwidth. For experimental validation, prototypes are designed and fabricated at the center frequency of 2.50 GHz using an FR-4 substrate with dielectric constant of 4.4 and loss tangent of 0.02. A good agreement is observed among the theoretical analysis, and the simulation and measurement results. The first fabricated prototype provides more than 64 dB SIC for the bandwidth of 110 MHz, while the second prototype achieved more than 60 dB SIC for 160 MHz bandwidth. In addition, the SIC of the antenna using the proposed DFN is high over the wideband frequency bandwidth as compared to conventional 180° ring hybrid feeding network. Due to ease of implementation and excellent performances, the proposed antennas have potential application for wideband in-band full duplex systems.