Research On Miniaturized Filters And Reconfigurable Filters

With the rapid development of modern wireless communication system,the frequency spectrum resources are increasingly limited,and the number of communication devices in the system is increasing.Filters as the indispensable device in wireless communication system.Reducing size or number of filters is the fundamental way to realize miniaturization of RF front-end,so the miniaturized filters and reconfigurable filters have become the focus of research.In addition,how to achieve high-performance miniaturized filter is particularly important.Therefore,this thesis focuses on the research of the methods to realize the miniaturization of filters,the out-of-band suppression technology and the realization of the tunable filter,and manufactures several miniaturized filters and tunable filters.The main content of this thesis is divided into the following three parts:1.Design of three-mode bandpass filter based on the theory of multi-mode resonator:Firstly,the field distribution characteristics of semicircular half-mode SIW resonator is analyzed according to the principle of multi-mode resonator.A three-mode bandpass filter based on half-mode SIW structure is designed by introducing a series of metal holes at a specific position of the resonant cavity to disturb the frequency of a specific resonant mode.The filter is miniaturized by using the structure of half-mode and three-mode resonator.2.Design of miniaturized wide stopband filters based on high order mode suppression theory:Firstly,the high order mode suppression theory is analyzed with substrate integrated waveguide as an example,and then two wide stopband filters are designed based on this technology.A wide stopband filter is designed by using the structure of quarter mode resonator and end-coupling theory.The stopband rejection of this wide stopband filter can reach 3.43f₀,and the speed of out of band rejection is improved by introducing transmission zeros.Compared with the full-mode structure,the area is reduced by more than half.Then,a grounded patch resonator is proposed.A wide stopband filter based on patch resonator is designed by using the high order mode suppression theory.The area of device is further reduced by introducing LC resonant mode.In addition,the stopband suppression width of the filter reaches 6.01f₀,and FBW reaches 40%,which meets the broadband characteristics of the filters.3.Design of reconfigurable filters based on substrate integrated waveguide:A tunable filter which can switch between single bandpass and dual passband is proposed based on the fluidity of liquid metal.The filter can be swithched among low frequency bandpass,high frequency band pass and dual bandpass by controlling the inflow or outflow of liquid metal through the non-metallic hole.Then,a tuning structure of“via posts with island”is proposed,which uses PIN diodes to control its on-off state.A tunable filter based on PIN diode tuning is designed,which can not only realize frequency switching,but also realize the independent tunable bandwidth of each frequency state.