Design of a Characteristic-Mode-Based Fully-Planar Antenna for Indoor In-Band Full-Duplex Radios

For indoor full-duplex in-band radios, ultra-low profile antennas with simple feed networks are highly sought. In this paper, a fully-planar, characteristic-mode-based, simultaneously transmit and receive (STAR) antenna with high isolation is presented. The proposed antenna utilizes two orthogonal characteristic modes for transmitting and receiving signals to achieve high isolation without a complicated self-cancellation circuit. The simulated and measured -10 dB reflection coefficient bandwidths of the proposed STAR antenna are 3.6% and 0.4%, respectively. The proposed antenna provides a simulated (measured) isolation greater than 48.4 dB (31.6 dB). The simulated peak gain is 4.4 dBi for both the transmit and receive links. The electrical size of the proposed antenna is 0.6λ×0.6λ×0.01λ where λ is the wavelength at 2.35 GHz.