Small Antenna with High Inter-port Isolation for In-Band Full-Duplex at HF Band

Antenna elements fitting within a 3 m radius sphere (ka = 1 at 15.9 MHz) are arranged in a 4-element circular array for operation in HF band. High inter-port isolation with the same polarization and similar radiation patterns in both transmit (Tx) and receive (Rx) modes simultaneously operating at the same frequency is achieved. The high isolation between Tx and Rx ports is achieved through the intrinsic self-interference cancellation capabilities of the employed modified Butler matrix beam-forming network consisting of one 90° and three 180° couplers fed in circular modes 0 and 1. The proposed antenna system is realized with smaller physical and electrical footprint and all near-field coupling affects are directly accounted for.