Theory And Design Of Wideband Reconfigurable Filter

Nowadays,the development of wireless communication technology is changing rapidly,the filter with frequency selection plays an important role in various communication systems,and the reconfigurable filter which can cover multiple frequency bands is one of the hot research directions.Based on the structure of SIW,this dissertation conducts in-depth research work from the theoretical analysis of filters to the design of practical reconfigurable filters.Based on the traditional conjugate matrix synthesis of filter,the coupling coefficient of resonator and the input / output coupling design,this paper presents a design method of reconfigurable center frequency,reconfigurable bandwidth and reconfigurable input / output coupling,and three new reconfigurable filters are proposed.Two filters use a half-mode substrate integrated waveguide(HMSIW)structure,compared with the full-mode structure,the half-mode structure is only half the size of the full-mode and its performance is close to that of the full-mode.In addition,the half-mold structure also loads the external tuning element easily.In this paper,a reconfigurable filter based on horizontal magnetic coupling structure is proposed firstly,and the bandwidth can be adjusted by switching the metal posts in the magnetic coupling window.In the form of magnetic coupling on the feeder,this weak coupling structure can improve the out-of-band rejection performance.Experimental results show that the center frequency of the filter can be continuously adjusted in the range of 1.72GHz~2.13 GHz,and the bandwidth can be switched individually at each frequency.Secondly,this paper presents another reconfigurable filter based on the magnetic coupling structure,this filter combines the SIW structure and the microstrip line,switching the microstrip line can change the resonant frequency of the resonator.The experimental results show that the center frequency of the filter tuning range is between 1.61GHz~1.96 GHz,and it also can switch bandwidth individually.Finally,this paper presents a reconfigurable filter based on a vertical hybrid electromagnetic coupling structure.The combination of the vertical coupling structure and the HMSIW structure can theoretically reduce the area of the filter by half again and provide a new idea for the miniaturization of the reconfigurable filter.The filter uses the form of direct coupling,this strong coupling structure will also increase the energy of higher harmonics,so this paper also proposes stopband optimization design.The hybrid electromagnetic coupling structure can introduce a transmission zero,besides,a reconfigurable band-stop filter is introduced and the designed filter is cascaded to improve the performance of the stop band,and the out-of-band rejection can be below-20 d B,the best one can be-60 d B below.The experimental results show that the center frequency of the filter tuning range is between 1.21 GHz ~1.72 GHz,close to 510 MHz,and the bandwidth can be tuned individually and continuously at each frequency.The simulation results of the reconfigurable filter designed in this paper are in good agreement with the experimental result.