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)
$\times 4$
(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.