title: A Compact, High Power Capable, and Tunable High Directivity Microstrip Coupler.
abstract: A coupler is an indispensable component to sample the forward and reflected power for the real-time radio frequency (RF) power monitoring system. The directivity of a coupler is a critical factor to achieve accurate RF power measurements. This paper proposes a microstrip coupler with a tunable high directivity circuit to accurately measure the reflected RF power. The directivity tuner composed of passive components adjusts phase and amplitude of the coupled RF signal, and cancel out the leakage signal from the RF input port at the coupled reflection port. The experimental results, which agree with simulation results, show that the microstrip coupler with the directivity tuner circuit has a compact size (~ 0.07 λgx 0.05 λg), high power capability (up to 1 kW), and high directivities (more than 40 dB) at operating frequency bands (f= 297.3 MHz, 400 MHz, and 447 MHz, respectively) for magnetic resonance imaging (MRI) applications.
authors.affiliation: Department of Electrical and Computer Engineering, University of Minnesota. He is now with the Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: Sung-Min
authors.initials: SM
authors.lastname: Sohn
authors.affiliation: Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: Anand
authors.initials: A
authors.lastname: Gopinath
authors.affiliation: Center for Magnetic Resonance Research (CMRR) and Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: John Thomas
authors.initials: JT
authors.lastname: Vaughan
keywords: RF power monitoring; directivity; isolation; magnetic resonance imaging (MRI); microstrip circuits; microstrip coupler; passive components