A Frequency-Tunable Rat-Race Coupler With Improved Performance

Abstract

Based on the design method of port equivalent impedance, a reconfigurable rat-race coupler with better performance is designed in this paper. First of all, on the premise of selecting the four-port network, the port equivalent impedance is obtained according to matching and isolation conditions. In addition, design a frequency reconfigurable matching network (MN) to match the port equivalent impedance to the port impedance across the entire frequency range. Last, by connecting the MN to the four ports, the adjustable operating frequency of the rat-race coupler is realized. This design method can simplify the coupler design. In order to verify the above proposed design method of reconfigurable coupler based on port equivalent impedance, we designed and measured a frequency reconfigurable rat-race coupler. The measured results show that the working frequency of the proposed coupler is continuously adjustable from 0.82 GHz to 2.26 GHz. In addition, the return loss and isolation are always better than 21 dB in the working frequency range of the coupler. Compared with similar couplers, the main advantage of this coupler is its superior performance over a comparable frequency adjustment range.