Design Of The Microstrip Band-pass Filters Based On SIR And SLR

With the development of contemporary communication system,various electromagnetic environments are becoming more and more complex,especially in the background of increasingly limited spectrum resources.The researchers have been committed to make communication devices operate in high-speed,high-quality and complex environments.In addition,communication devices should support and apply in multiple standard protocols and make full use of limited spectrum resources.As one of the foremost RF devices in the communication system,filter carries the important mission of frequency selection.Requirement to the performances of filter are also increasing.The specific contents contain that,they not only need the filter to be compact,easy to integrate and produce at low costs,but also require it to have low insertion loss,high-band selectivity and high-band rejection.Furthermore,the development of multi-mode communication are getting more and more rapid,which requires the filter to be compatible with various modes at the same time in 2G(GSM,CDMA),3G(CDMA2000,WCDMA,TD-SCDMA,WIMAX),4G(TDD and FDD),and Bluetooth,and make full use of good spectrum resources.Therefore,the multiband filter is the focus of today's communication development.The main content of this paper is as follows:Firstly,this paper enumerates the domestic and foreign researches in microstrip band-pass filters.We also list several methods of designing band-pass filters,summarize their advantages and disadvantages through in-depth comparison.Secondly,this paper gives the design methods of the filter,which contains the main design index,odd-even mode analysis and the basic theory of stepped-impedance resonator(SIR).Lastly,this chapter introduces the working principle of the quarterwavelength,half-wavelength,and full-wavelength resonators in detail.Thirdly,we compare the open circuit stub-loaded resonators with short circuit stub-loaded resonators(SLR),summarize their advantages and disadvantages.And based on short circuit SLRs,we design a dual-mode dual-band microstrip filter,it can be used in the WLAN frequencies with 2.4GHz and 5.2GHz,whose relative bandwidth are 7.8% and 7.1%.By exploring the size of the coupling gap,it can be concluded that the coupling gap could change the position of transmission zeros.Fourthly,in order to filter out unwanted clutter in multiple frequency bands at the same time,based on short-circuit-loaded resonators,three filters including single-band,dual-band,and triple-band are proposed,and the proposed three can be used in WIMAX/WLAN applications.By slitting the resonator,the augments in insertion loss near the third passband are eliminated.Finally,the complete reconfigurable filter is introduced.The introduced short circuit stub-loaded resonator works as a “carrier”.The resonator mainly contains a certain gap,both capacitor and inductance can be inserted in the gap to form a reconfigurable filter.When the capacitor is connected to the filter,the filter is a dual-band.Whereas the inductance is connected,the filter exhibits a single-band characteristic.