A Study On High Isolation Branch Line Directional Coupler With A Short Branch Section

The directional coupler is a common microwave passive component, it has been widely used in the RF front-end in wireless system. In particular, the directional coupler is often used as a key component isolating transmission and reception in the wireless transceiver system of same frequency. But the isolation of the conventional coupler is low and operating bandwidth is narrow, the system can not meet the requirements. In this paper, a branch line directional coupler for the study, the main focus on how to improve their isolation and increase bandwidth to conduct in-depth research work. The main work and innovation of this paper include:(1)According to the principle of destructive power, a shorted stub has been added in its couple d microstrip port to design a 3dB short circuit with double branch stub directional coupler. This met hod is simple in structure, easy to implement, and can greatly improve the coupler isolation. Compl eted the processing and measurements of a test sample to verify the effect of the short-circuit stub li nes are used to improve the branch line directional coupler isolation degree. And the shortcoming of operating bandwidth is not obvious improved.(2)Based on the dual branch line directional coupler, an effective method was summed to improve its operating bandwidth: Increase the coupling path, and to design a directional coupler 3dB-third branch, the coupler can significantly broaden the operating bandwidth. On the basis of the 3dB with short circuit stub double branch line directional coupler, a 3dB with short circuit stub-third branch directional coupler was designed. The improved directional coupler is largely widened the operating bandwidth, and improve the isolation.