Asymmetric Differential Filtering Device And Its Key Technologies

Differential filtering device has important research significance in the modern communication system because one device not only provides filtering function for the microwave system,but also can effectively improve the immunity to electromagnetic crosstalk and environment noise,and connect with other differential circuits directly.Differential filtering device includes a single function differential filter and multi-function filtering power divider etc.The traditional differential filtering device mainly uses the symmetrical way to realize the differential-mode(DM)filtering and common-mode(CM)suppression.In such way,the circuit size of the differential filtering device is usually twice as much as that of corresponding single-ended filtering device,which makes the size of differential filtering device large.In order to reduce the size and simplify the structure,the asymmetric differential filtering device is proposed in this paper.The main research contents include the microstrip impelmention technology and the substrate integrated waveguide(SIW)implemention technology of asymmetric differential technology.Three kinds of asymmetric differential filtering devices are proposed.First,an asymmetric differential filter based on microstrip line is proposed.For the basic design,three cascaded half-wavelength microstrip lines loading asymmetric differential microstrip feeders are utilized to achieve the basic functions of wideband DM transmission and CM suppression.Besides,the proposed basic design also has the advantages of small size,low loss,and simple structure.In the paper,the extraction process of standard S paremeters and mixed S parameters is detailedly given to provide a solid theoretical foundation for the following designs.In order to obtain a wide CM suppression response without increasing the circuit size,two cascaded quarter-wavelength coupled lines are used to replace the middle half-wavelength microstip line of the basic design,which can obviously suppress the CM signal and improve the frequency selectivity as well.In order to further improve the frequency selectivity,one half-wavelength stepped impedance stub is loaded at the center of the cascaded coupled lines,which can produce multiple DM transmission zeros and obtain high frequency selectivity.Compared with the reported microstrip differential filters,the proposed design not only realizes small size,but also has the advantages of low loss,high frequency selectivity,and wide CM suppression.Second,an asymmetric differential filter based on SIW is proposed.For this design,the asymmetric microstrip differential feeders are utilized to excite half-mode SIW(HMSIW)multimode resonator to make the TE ^HM₁₀₃,TE^HM₁₀₄ and TE^HM₁₀₅ modes of the HMSIW multimode resonator operate in DM and TE^HM₁₀₂ and TE^HM₁₀₆ modes operate in CM.As a result,the features of wideband DM transmission and CM supperssion can be achieved.The design only adopting single-layer HMSIW multimode resonator combined with asymmetric distribution reduces the circuit size and loss effectively.The slots etched on the surface of the resonator improves the degree of freedom of filter tuning and makes up for the slightly performance deviations made by manufacturing error.Compared with the reported differential filters based on SIW,the proposed design not only realizes small size,but also effectively balances low loss,wideband,and performance fine-tunning caused by the manufacturing process.Finally,a 1-to-n(n=2,3...)way asymmetric single-ended-to-differnetial filtering power divider(SETDFPD)based on SIW is proposed.The proposed design adopts the distribution of n 32nd-mode SIW multimode resonators symmetrically connected to the common single-ended input port.n pairs of differential output ports are used to excite the resoantor,which makes TE₁₀₃^32nd and TE₁₀₅^32ndmodes of 32nd-mode SIW resonator operate in DM and TE₁₀₁^32nd and TE₁₀₇^32nd modes operate in CM.As a result,the wideband filering power dividing response can be achieved.The design adopting single-layer 32nd-mode SIW resonator combined with asymmetric distribution reduces the circuit size and loss effectively.To validate the approach of 1-to-n way SIW SETDFPD,1-to-3 way SIW SETDFPD is simulated and demonstrated.Compared with the reported SETDFPDs,the proposed approach not only realizes small size,but also has all the functions of 1-to-n way,filtering,single-ended-to-differential power dividing,and CM suppression.