Design Of Substrate-integrated Filter With Tunable Center Frequency Reconfigurable Bandwidth

As the future direction of the development of communication systems,reconfigurable communication systems draw more and more attention.As a key component of microwave reconfigurable communication system,tunable RF filters have been a hot topic in recent years.In this paper,from the theoretical analysis to the actual design,the tunable filter is launched a related study.Firstly,based on the theory of traditional filter design,the traditional J / K converter and the coupling coefficientijM are transformed into a function J(?),K(?),()ijM ? with respect to the frequency,which provides theoretical guidance for tunable filter design.Based on the design theory of tunable filter,from tunable resonator design to tunable coupling design--the coupling between the cavity as well as the coupling between input and output.Two novel filters with tunable center frequency and reconfigurable bandwidth are proposed.In this paper,firstly,a fully tunable HMSIW filter loaded a semi-circular metal sheet is designed and implemented.Compared to the traditional full-mode structure,the size of the filter is reduced by halves and the half-mode structure provides the physical space for loading the tuning element and the feeder line.Due to the first-invented semi-circular metal sheet,the size of the cavity can be further reduced.The first-invented semi-circular metal sheet also brings the advantages of improving the tuning precision and decreasing the difficulty of selecting the tuning element.The measured results are in good agreement with the simulation results,both the tuning range and the cavity Q value(insertion loss)can be achieved or even better than the performance of the ajustable SIW filter which metioned in domestic and international literatures.Secondly,in this paper,a SIW filter combining with the microstrip line is proposed,designed and implemented,the frequency tuning is realized by switching microstrip lines with different electrical lengths,and the bandwidth tuning is achieved by switching the metal posts at the coupling window.Multi-band and multi-bandwidth switching was achieved through testing.The tunable filter utilizes multilayer process to combine microstrip lines with a "coaxial-like" SIW resonator without increasing the size of the resonator,which provides a new idea for designing adjustable filter using microstrip and SIW structure.Based on the passband design,this paper presents the concept of stopband design,a new "concave" fully adjustable filter is designed,two programs to improve the performance of the stop band is proposed.One of the means,transmission zeros are introduced through multi-stage cross-coupling.Another,tunable low-pass filter with multiple transmission zeros cascades with a band-pass filter,which is used for inhibitioning the parasitic passband,the low pass whose cut-off frequency and transmission zeros adjustable is used to fine tune the parasitic passband that vary as tuning of bandwidth and frequency.The measured results shows that the proposed structure achieves high parasitic suppression and band bandwidth of stop-band.The results of the proposed filter are in good agreement with the simulation results,and the expected design index is achieved.Compare with the performance of tunable filter the current frontier references are presented,the filters designed in this paper have reached the level of the international leading SIW tunable filter.