Analysis And Design Of Novel Planar Broadband/Multiband Filtering And Coupling Circuits

With the rapid development of microwave technology,modern communication systems are becoming increasingly complex,and the requirements for the performance of communication system components are becoming higher and higher.Filters and couplers are important components of microwave passive circuits,and their performance will directly affect the performance of the entire communication system.In the RF front-end circuit,the filter and the balun are usually used together.If they are simply cascaded,which will occupy a large space in the entire system,and hinders the trend of miniaturization of the entire system,and the insertion loss of the entire system will be high.So,it is necessary to integrate the filter and balun together.There are many noise signals in complex communication systems.Balanced circuits can effectively suppress common mode interference.Therefore,balanced filters have been widely used in communication systems.With the new communication frequency band standards being constantly proposed,microwave devices that work in a single frequency band are difficult to meet the requirements of modern communication systems.Therefore,research on microwave devices supporting multiple frequency bands is one of the hotspots in modern microwave technology.The problem of signal crossover is often encountered in planar microwave circuits.Crossovers can cross two input signals,and the signals are isolated from each other.Based on the even/odd mode analysis method,this paper analyzes and designs several planar broadband/multiband filters and coupler circuits.The main work of this article is as follows:1.Wideband filtering balun using Schiffman phase shifter: The improved Schiffman phase shifter is added to the Wilkinson power divider to achieve 180 ° phase difference,and good isolation is achieved between two output ports.A quarter-wavelength impedance transformer and a quarter-wavelength coupling line are combined to get a wideband balun.By connecting a half-wavelength open-circuit branch in parallel,the filtering characteristics are realized.2.Wideband balanced filter using a Marchand balun: A balanced filter with good common mode rejection is realized based on Marchand balun structure.By connecting a paralleled stepped impedance resonator,two transmission zeros are obtained at both ends of the passband,which improves the structure’s differential mode passband selectivity and common mode suppression.At the same time,the bandwidth of the structure is increased by connecting a paralleled quarter-wavelength short-ended branch.3.Multi-band crossovers based open/shorted coupled lines: Based on the cascade structure of the branch line coupler,open/shorted coupling lines are loaded to achieve a crossover working in dual-band/triple-band,which has good in-band matching and isolation effects.The center frequency and bandwidth of each working frequency band can be adjusted in a wide range by changing the impedance of the coupler’s parity mode.