Wave Single Branch Line Coupler And Its Application In The Mixer

The directional coupler is a kind of directional power divider, which is widely used in microwave system. This dissertation presents a simple and easy-facilitative structure of the directional coupler—single-branch directional coupler. Base on this coupler, a W-band single-balanced mixer is developed. In the introduction, it is briefly introduced the directional coupler and millimeter wave mixer developments.In the research of the single-branch directional coupler, the directional coupler's basic technical features are introduced. Then, we discuss the working principle of the single-branch coupler. In order to analyze and design single-branch directional coupler, both the parity-method and the Green function are used. At the same time, HFSS simulation software gives an optimized design, and some results are achieved in W-band. From 85 GHz to 91GH, the imbalance between the two output ports of the coupler is less than 1 dB with the return loss and isolation greater than 10 dB. In the analysis of results, the further recommendations for improvement are given.In order to verify the practicality of the single-branch directional coupler, a W-band single-balanced mixer is designed. Based on the systematic analysis of the mixer principles and the single-balanced mixer circuit model, we put forward the implementation of the single-balanced mixer with a single-branch directional coupler. The ADS simulation software is used to analyze the single-balanced mixer's nonlinear characteristics, and the HFSS simulation software is used to optimize the match of the single-balanced mixer. Then, the fabrication and testing of the circuit are done. In the 85 GHz～95GHz, the conversionloss of the mixer is less than 22.4dB.In addition, the waveguide to microstrip transition and the IF low pass filter are improved, which are used in the mixer. The simulation results show that the transition in the 85 GHz～95GHz band has return loss of greater than 28 dB, and the low pass filter bandwidth at the short-point is 21.5GHz.In conclusion, it is summed up that the single-branch directional coupler can be successfully used for the W-band single-balanced mixer. The application in the mixer reflects the practical value of the single-branch directional coupler. At the same time, the inadequacies of the topics are summed up and the recommendations for improvement are proposed.