Compact Wideband Dual-Polarized In-Band Full-Duplex Antenna Subsystem

A compact, wideband, circulator-less, quasi-monostatic, and dual circularly polarized simultaneous transmit and receive (STAR) antenna subsystem is presented. The configuration consists of a sequentially rotated array (SRA) of four combined TEM horn-loop antennas for transmitting (TX) and a four-arm sinuous antenna for receiving (RX). The sinuous antenna is placed at the center of the SRA and both are excited with 2 (inputs) x 4 (outputs) Butler matrix beamforming networks (BFNs). Due to the geometrical symmetry and applied excitation, any self-interfering TX signal is canceled at the co-polarized receiving port leading to high TX/RX isolation. Practically, the achieved isolation is limited by the geometrical and electrical asymmetries attributed to the fabrication, assembly, and BFN imbalances. The dual-polarization is achieved by exciting the proper ports of the BFNs. The mechanically robust radome-enclosed prototype is tested and measured with a self-interference cancellation above 40 dB recorded across the bandwidth of 0.8-3 GHz. Acceptable gain, axial ratio, and symmetric beams are obtained over all four ports. The overall compact size and high-isolation ultrawideband operation make the proposed antenna subsystem feasible candidate for many practical STAR systems.