Study And Design Of Controllable Dual-band Bandpass Filter Based On The Substrate Integrated Waveguide

Filter plays an important in modern wireless communication system as a typical microwave passive component,and it can be used to for band allocation,channel isolation and external interference and harmonics suppression.With the rapid development of modern wireless communication technology,the higher requirements of the performance of filters have been raised.Especially with the condition of limited spectrum resources,it is significant and important to design dual-band microwave filters.In recent years,Substrate Integrated Waveguide(SIW)is proposed by researchers as a new technology,which has been widely used in designing filters due to its advantages of large power capacity,low radiation loss,low cost and easy integration with other planar circuits.Microwave filters based on SIW technology,characterized by the miniaturization,easy integration and low cost,can satisfy the demand of modern communication systems.In this paper,three microwave filters are designed based on the SIW technology according to the comprehensive theory and design method of filter.All of the proposed filters have the advantages of good in-band performance,high selectivity and good outof-band rejection,and the measured results agree well with the simulated ones.Main achievements are as followed:1.A compact broadband bandpass filter based on composite right/left-handed(CRLH)and Quarter-Mode Substrate Integrated Waveguide(QMSIW)is presented and analyzed in this paper.A size reduction is implemented by etching the CRLH interdigital slots on the QMSIW to introduce a lower resonant frequency less than that of the original QMSIW.Moreover,the proposed structure shows the characteristics of low quality factor and high coupling coefficient that make it a good solution to design a broadband bandpass filter.The measured insertion loss is less than-1.8GHz at 4.43 GHz with a fractional bandwidth(FBW)of around 22%.2.A novel hybrid array resonator structure,which is composed of four complementary split-ring resonators(CSRR)and two central-folded stripline resonators(CFSR),is proposed and analyzed in this paper.Two proposed hybrid structures are cascaded and etched on the SIW to form an individually controllable dual-band bandpass filter,meanwhile,transmission zeroes are introduced in transmission responses which can increase the isolation of two passbands and out-of-band rejection of the filter.In measured results,center frequencies of the proposed filter are located in 4.62 GHz and 5.98 GHz with FBWs of 7.25% and 4.28%,respectively.The corresponding insertion losses are-2.1dB and-2.53 dB.3.A compact dual-band bandpass filter is proposed in this paper by etching embedded coplanar waveguide(ECPW)structure and coaxial waveguide resonator(CWR)on SIW cavity.In measured results,two passbands are centered at 8.41 GHz and 14.29 GHz with FBWs of 21.2% and 7.3%.The measured insertion losses are-1.28 dB and-1.91 dB,respectively.Mixed coupling between the proposed ECPW and the SIW cavity can produce two transmission zeroes at the upper stopband of the first passband,meanwhile,another transmission zero located at the upper stopband of the second passband is generated by the cross coupling between the proposed CWR and source/load.Three transmission zeroes can significantly improve the selectivity of the designed filter.In addition,out-of-band suppression drops below-30 dB when stepped-impedance open stubs are loaded at input/output of the designed filter,indicating that the upper stopband characteristics of the filter is effectively improved.