Research On Reconfigurable Filter Based On LTCC Technology

With the continuous development of modern communication technology,especially mobile communication technology,new communication standards emerge in endlessly.Integrated multi standard communication system has gradually become the main solution to provide communication services.Radio frequency filter is one of the key device of frequency selection in wireless communication system,and its reconfigurability is a research hotspot in industry and academia.At present,the common way to realize the filter reconfiguration is to add tunable elements in the resonator,including PIN diode,varactor diode,and the variable capacitance of piezoelectric materials,and use these tunable elements to control the center frequency and working bandwidth.Among these methods,PIN diode and varactor have the advantages of fast response speed and easy integration with RF circuits.At the same time,the continuous development of manufacturing technology provides a strong support for the design of RF circuits,in which the low temperature co-fired ceramic technology has attracted more and more attention in the field of microwave circuits,and can help RF filter to realize miniaturization.This thesis is the research on reconfigurable RF filters based on LTCC technology,the specific research content is divided into the following four parts:(1)The application of capacitor-loading technology in quarter wavelength resonator is analyzed,which can greatly reduce the circuit size.The combline filter is designed by using the proposed resonator,and the transmission zeros are introduced on both sides of the passband by adding electric coupling as cross-coupling,which effectively improves the filter selectivity and stopband suppression.Finally,according to the above principle,four filters are designed and manufactured successfully by LTCC process.The center frequencies are 1.07 GHz,1.12 GHz,1.35 GHz and 1.47 GHz respectively.The measured return loss is better than 10 dB.(2)Using PIN diode as RF switch element,two kinds of reconfigurable filter architecture based on filter bank and PIN diode are designed,and two kinds of filter implementation schemes with four states reconfigurable are given correspondingly.In the first scheme,the feed network and the filter bank are integrated in a single substrate.The central frequency tunable range is 1.66 GHz ~ 2.2GHz,and the return loss in each state is lower than-15 dB.In the second scheme,the feed circuit is designed separately,and then the feed circuit and the filter bank are welded together after processing.Compared with the test separately,the insertion loss in each state is 0.2db ~ 0.3dB lower.The filtering effect of the two schemes is good,and both schemes have strong expansibility.(3)A fourth order reconfigurable LTCC filter is proposed.Parallel plate capacitor and varactor are loaded simultaneously in a quarter wavelength resonator,and the resonant frequency is tunable while the size of the resonator is reduced.By introducing cross coupling between resonators 1 and 4,two transmission zeros are generated on both sides of the passband,which achieves steep sideband and good stopband suppression.The test results show that the filter center frequency is continuously adjustable between 1.27 GHz and 1.59 GHz,the insertion loss is stable between 4.2dB and 2.2dB,and the return loss is better than 11 dB.(4)Two miniaturized filters based on LTCC process are studied and proposed.Firstly,the application of controllable mixed electrical and magnetic in SIW resonator is studied.The third-order inline SIW filter can introduce transmission zeros on both sides of passband,its center frequency is 12.03 GHz,and the return loss is better than 20 dB.Then,by introducing evanescent mode loading in SIW resonator,the filter volume is miniaturized,the center frequency is 10.1GHz,and the return loss is 19 dB.Secondly,the parallel plate capacitor effect is produced by using the wide side strong coupling of the multi-layer stripline,which greatly reduces the length of the half wavelength resonator to one sixth of the wavelength.The filter using zero degree feed structure is designed with the proposed resonator.Transmission zeros are introduced into both sides of the passband,and the filter miniaturization and high selectivity are realized.The measured center frequency is 2.13 GHZ,the minimum return loss in band is less than 16 dB.