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Miniaturized tunable extended eight-port hybrid coupler for 1.5 T MRI

Published online by Cambridge University Press:  03 August 2022

Zachary A. Colwell Open the ORCID record for Zachary A. Colwell [Opens in a new window]  and
Sung-Min Sohn Open the ORCID record for Sung-Min Sohn [Opens in a new window]
Zachary A. Colwell
Affiliation:
School of Biological and Health System Engineering, Arizona State University, Tempe, Arizona, USA
Sung-Min Sohn*
Affiliation:
School of Biological and Health System Engineering, Arizona State University, Tempe, Arizona, USA
*
Author for correspondence: Sung-Min Sohn, E-mail: smsohn@asu.edu
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Abstract

This paper presents a miniaturized, tunable, high-power, eight-port hybrid coupler, based on a lumped element hybrid coupler topology. The 90° hybrid couplers are ubiquitous elements used for feeding RF coils in quadrature in magnetic resonance imaging (MRI) systems. Due to the low Larmor frequency (64 MHz) of 1.5 T MRI, distributed elements are too large for practical circuits to drive multi-port RF coils. Thus, miniaturization with MRI-compatible, non-magnetic, and high-power components is necessary. First, a miniaturized hybrid coupler is proposed for MRI systems with non-magnetic variable capacitors. Afterwards, the miniaturization methodology is applied to develop an eight-port coupler, capable of supporting both a transmit and a receive quadrature RF coil system. The high-power (up to 1 kilowatt) extended coupler measures 10 cm × 6 cm. Test results show that each port has a return loss of more than 16 dB, each input-isolated port is isolated by more than 24 dB, and each output has an insertion loss of less than 2.5 dB and output phases of 0.0°, 90.8°, 182.1°, and 278.7°.

Keywords

Antenna feedhybrid couplermagnetic resonance imaging (MRI)passive circuits
Type
Biomedical Applications
Information
International Journal of Microwave and Wireless Technologies , Volume 15 , Issue 5 , June 2023 , pp. 805 - 809
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Copyright
© The Author(s), 2022. Published by Cambridge University Press in association with the European Microwave Association

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