Research And Design Of Dual-band And Multi-band Branch Line Directional Couplers

With the rapid development of modern wireless communication systems,microwave devices are constantly being upgraded.Devices that can work in multiple frequency bands at the same time can meet the requirements of complex circuit systems.Branch line directional couplers are important passive devices in microwave circuits which play an important role in microwave circuit systems.Therefore,dual-frequency and multi-frequency branch line directional couplers have received extensive attention and research.This thesis describes the design methods and research status of dual-band and multi-band branch line directional couplers of in recent years and introduces the basic theory of directional couplers and microstrip lines.This thesis analyzes several dual-frequency impedance converters based on coupled lines.Through transmission line theory and even and odd modes analysis method,the theory of the converters is analyzed and calculated deeply.The converters are applied to the dual-band branch line directional couplers which are verified by simulation.In addition,based on the dual-frequency impedance converter composed of the coupled lines and the parallel open stubs,a dual-band branch line directional coupler working at 0.6/3.6 GHz is designed and manufactured.The dual-band branch line directional coupler structure is adjusted and optimized using stepped impedance transmission lines and spur lines.Compared with the existing dual-band branch line directional couplers,the range of the operating frequency ratio larger.The amplitude difference between the two output ports is small and the dual-band coupler has high performance.This thesis presents a quad-band impedance converter based on coupled lines and open stubs,which can be used in the design of quad-band branch line directional couplers.The correctness of the theory is verified by even and odd modes analysis and simulation.In addition,a quad-band branch line directional coupler working at 0.7/1.64/4.09/5.03 GHz is designed and manufactured.The measurement results are in good agreement with the theory.Compared with the existing quad-band branch line directional couplers,the quad-band branch line directional coupler has a novel structure,and the solution and design method are accurate and simple.The designed coupler have certain advantages in design method.