Received 28 January, 2021; revised 3 March 2021; accepted 6 March 2021. Date of publication 19 March 2021; date of current version 22 April 2021. Digital Object Identifier 10.1109/OJAP.2021.3067471 Dual-Polarized High-Isolation Antenna Design and Beam Steering Array Enabling Full-Duplex Communications for Operation Over a Wide Frequency Range MAKSIM V. KUZNETCOV 1 (Graduate Student Member, IEEE), SYMON K. PODILCHAK 2 (Member, IEEE), ARIEL J. MCDERMOTT 1 (Student Member, IEEE), AND MATHINI SELLATHURAI 1 (Senior Member, IEEE) 1 Sensors, Signals, and Systems, Heriot-Watt Universty, Edinburgh EH14 4AS, U.K. 2 Institute of Digital Communications, The University of Edinburgh, Edinburgh EH9 3JW, U.K. CORRESPONDING AUTHOR: M. SELLATHURAI (e-mail: m.sellathurai@hw.ac.uk) This work was supported in part by the U.K. Engineering and Physical Sciences Research Council under Grant EP/P009670/1. ABSTRACT A new dual-polarized antenna and array are presented for In-Band Full-Duplex (IBFD) applications, offering high inter-port isolation. The single-element antenna system consists of four H-shape slots, stacked patches for wide bandwidth, and two external hybrid couplers. The multilayer antenna is well matched from about 2.1 to 2.4 GHz and provides high isolation in this frequency range in excess of 60 dB. Two different prototypes are simulated and measured to highlight the design process. In addition, a new and compact hybrid coupler with excellent phase and magnitude stability is also presented for improved antenna radiation and IBFD performances. When compared to other similar types of hybrid coupler and antenna systems, the proposed configurations are simple to manufacture, provide a higher isolation bandwidth (10%), and higher gain of 7.3 dBi with cross-polarization levels of 30 dB or lower. The single-element design was also extended to a 2×2 array and studied for different beam steering and feeding scenarios. The operating bandwidths and isolation values offered by these S-band antenna and array systems can support new data link possibilities for beam steering and future low-cost IBFD wireless networks by simple antenna fabrication. INDEX TERMS Dual-polarization, double-differential antenna, full duplex, isolation, simultaneous transmit and receive (STAR). I. INTRODUCTION W ITH the advancements of wireless communications, full-duplex (FD) antenna systems are once again a topic of interest [1]. These systems are attractive not only because of their ability to simultaneously transmit and receive thus requiring less antenna hardware, but also, due to the possibility of increased channel capacity and spectrum density [2]–[4]. However, due to this simultaneous trans- mit and receive capability, these systems can experience high self-interference (SI) where the transmitted signal is so strong that it suppresses the received signal making FD data transmission challenging. One of the first implementations of FD systems was in radar. Due to technological limitations, the only way to reduce interference was to control the transmitting power which causes the operating range of the radar to be limited. With more recent advances, there are now a number of tech- nologies that can be employed to suppress this interference. One way to cancel out the SI is to implement an analogue cancellation mechanism, for example, using coupler phase compensation systems to cancel out the received signal or expensive and bulky circulators which might have only 20 or 40 dB of isolation [5], [6]. Another method of SI suppres- sion is digital cancellation. Examples of digital cancellation This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ VOLUME 2, 2021 521