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A tuneable rat-race coupler for full duplex communications

Published online by Cambridge University Press:  26 May 2021

G. T. Watkins Open the ORCID record for G. T. Watkins [Opens in a new window]
G. T. Watkins*
Affiliation:
Bristol Research and Innovation Laboratory, Toshiba Europe Limited, 32 Queen Square, Bristol, BS1 4ND, UK
*
Author for correspondence: G. T. Watkins, E-mail: [email protected]
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Abstract

Full duplex (FD) could potentially double wireless communications capacity by allowing simultaneous transmission and reception on the same frequency channel. A single antenna architecture is proposed here based on a modified rat-race coupler to couple the transmit and receive paths to the antenna while providing a degree of isolation. To allow the self-interference cancellation (SiC) to be maximized, the rat-race coupler was made tuneable. This compensated for both the limited isolation of the rat race and self-interference caused by antenna mismatch. Tuneable operation was achieved by removing the fourth port of the rat race and inserting a variable attenuator and variable phase shifter into the loop. In simulation with a 50 Ω load on the antenna port, better than −65 dB narrowband SiC was achieved over the whole 2.45 GHz industrial, scientific and medical (ISM) band. Inserting the S-parameters of a commercially available sleeve dipole antenna into the simulation, better than −57 dB narrowband SiC could be tuned over the whole band. Practically, better than −58 dB narrowband tuneable SiC was achieved with a practical antenna. When excited with a 20 MHz Wi-Fi signal, −42 dB average SiC could be achieved with the antenna.

Keywords

Full-duplexpassive components and circuitsRF front-ends
Type
Passive Components and Circuits
Information
International Journal of Microwave and Wireless Technologies , Volume 14 , Issue 5 , June 2022 , pp. 566 - 572
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Copyright
Copyright © The Author(s), 2021. Published by Cambridge University Press in association with the European Microwave Association

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