Sohn Sung-Min, Gopinath Anand, Vaughan John Thomas
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.
Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455 USA.
IEEE Trans Microw Theory Tech. 2016 Oct;64(10):3217-3223. doi: 10.1109/TMTT.2016.2602835. Epub 2016 Sep 12.
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 λ x 0.05 λ), high power capability (up to 1 kW), and high directivities (more than 40 dB) at operating frequency bands ( = 297.3 MHz, 400 MHz, and 447 MHz, respectively) for magnetic resonance imaging (MRI) applications.
耦合器是实时射频（RF）功率监测系统中用于采样正向和反射功率的不可或缺的组件。耦合器的方向性是实现精确射频功率测量的关键因素。本文提出了一种具有可调高方向性电路的微带耦合器，用于精确测量反射射频功率。由无源元件组成的方向性调谐器可调整耦合射频信号的相位和幅度，并在耦合反射端口消除来自射频输入端口的泄漏信号。实验结果与仿真结果一致，表明具有方向性调谐器电路的微带耦合器尺寸紧凑（约0.07λ×0.05λ），功率容量高（高达1kW），并且在磁共振成像（MRI）应用的工作频段（分别为297.3MHz、400MHz和447MHz）具有高方向性（超过40dB）。
