Design For Coplanar Waveguide Filter Based On Separate Electric And Magnetic Coupling

In recent years, with the rapid development of microwave and millimeter wave integrated circuits, especially monolithic microwave integrated circuit(MMIC)technology, coplanar waveguide structure has received wide attention. Coplanar waveguide(CPW) has many advantages of planar circuit. Compared with microstrip, it has better electromagnetic compatibility. This paper has studied the basic theory and design method of the separate electric and magnetic coupling(SEMC) CPW filters and CBCPW filters. It has the performance of controlled adjustable, high frequency selectivity, etc.Firstly, the research status of the coplanar waveguide is briefly described and the basic theory on microwave filter is researched. Secondly, the multi-band bandpass filters have been proposed base on the separate electric and magnetic coupling resonator and the defected coplanar waveguide structure resonator, their design methods have been studied. SEMC Stepped impedance resonators are used in filters design. Electric and magnetic coupling are introduced between a pair of SIRs by the microstrip gap and the grounded via, respectively. It is convenient to control the electric and magnetic coupling, due to they are in different coupling paths. It is noted that electric field centers on SIRs ends coupling gap, it can be equated with a coupling capacitor, and the magnetic field centers on grounded via, the two coupling paths are of the electric and magnetic ones, respectively. A pair of transmission zeros can be realized with SEMC resonator adding the source-load coupling. The transmission zeros at the lower and higher stopband are attribute to electric-dominant coupling and magnetic-dominant coupling, respectively. Transmission zeros(TZ) can improve the filter's frequency selectivity and out band suppression greatly. With the Separate electric and magnetic coupling design of coplanar waveguide(CPW) filter, Comparing to the relationship of the frequency? transmission zeros? coupling coefficient and the resonator physical size, we gives the resonator element equivalent transmission line circuit and the equivalent lumped circuit model. According to these models,we respectively deduced frequency ? coupling matrix ? electrical coupling and magnetic coupling coefficient expressions. Then, the dual-band resonator is designed by using the combination of the resonator. In this way, It is easy to design the dual-band bandpass filter with good frequency performance.Finally, this paper presents a conductor backed CPW(CBCPW) filter. This filter in the application of the CBCPW structure at the same time, It also used the principle of the separate electric and magnetic coupling to achieve separate control transmission zeros. Through the comparison of the electromagnetic field distribution between CBCPW and CPW, the electric field and the magnetic field of CBCPW resonator are more concentrated than the CPW resonator, and the intensity of the electromagnetic field is stronger. This shows that the CBCPW structure has better electromagnetic compatibility characteristics. CBCPW filter has better filtering performance.