For The Optimization Design Of The Coupling Line Broadband Directional Coupler

The analysis and study of coupled-line establishes structural basis for coupled-line directional couplers and greatly promotes theirs development.Depending the synthesis theory of coupled-line directional couplers,we can easy to design multisection and tapered coupled-line directional couplers that facilitate the engineering practice.Based on the structure of coupled striplines,this paper elaborates design methods of the asymmetric multisection and tapered coupled-line directional coupler.To achieve faster synthesis,the author gives series of synthesis programs in the index.In the design of broadband asymmetric multisection parallel-coupled line directional coupler,we found that directional performance and VSWR gradually deteriorated as the frequency increasing,which the traditional theory couldn’t explain. For this problem, the author has done the in-depth study,gived the reasons that may be caused by the internode region discontinuity and adopted load capacitance branches section to compensate for the discontinuity.A-6dB directional coupler working in the0.8～2.5GHz was designed.3D simulation model was established in HFSS.By Fixing the width of all shunt capactive stubs to lmm and optimizing the length of the stubs,the author obtain the optimal length.By comparing the simulation data of loading shunt capactive stubs before and after, the feasibility of this method was verified.In the design of ultra-wideband asymmetric tapered coupled-line directional coupler,two problems was primarily faced. One was how to improve directional performance and VSWR in the high-end of operating frequency.The other was how to optimally design directional coupler of arbitrary coupling.For the first problem,two way can be adopted:one is by introducing compensating shunt capacitances in a number of cross sections of coupled and signal lines,the other is by introducing periodic sawtooth in one end of tight coupling.This paper chose the second methods. Depending on HFSS and optimizing the number,location, spacing and height of sawtooth,a-20dB directional coupler working in the0.5～20GHz was designed,manufactured and measured. Comparing simulated and measured data,we found that the coupling basically matched between each other,the isolation had a little deteriorated and the port reflectometer deteriorated about20dB.Through analyzing the results,the deteriorated reasons maybe caused by mismatched between50Ω signal line and the SMA connector,but the feasibility of this method was verified.Combined the previous theoretical with the circuit simulation software,a new design method of arbitrarily weak coupling tapered line coupler was presented. The author discussed the comprehensive process in detail and gived the corresponding comprehensive program. At last,the author gived the circuit simulation results verificating this method’s feasibility.