Research And Design Of Novel Waveguide Filter Based On Evanescent Mode

Modern wireless electronic communication systems are developed toward the trend of high performance,high integration and high stability.Along with the updating in a variety of radio technologies and applications,the resources of available spectrums are increasingly strained.For the sake of efficiently selecting desired frequency,decreasing system signal attenuation,suppressing interference between signals,the filter in wireless electronic communication systems should have the characteristics of high selectivity,low insertion loss,far spurious frequency band,compact size and so on.The main content of this thesis focuses on the suppression of spurious passband in a waveguide filter--evanescent mode technology,and as a basis,develops a novel resonant structure with strong coupling,high power and small size,which can significantly improve the performance of the filter.Evanescent mode technology can make the electromagnetic wave transmitted in the waveguide maintain the cut-off state.Cutoff waveguide can be equivalent to a "(47)" or "T " inductive network,in which the evanescent mode waveguide filter can be constituted by loading the appropriate capacitive components.The innovation of the new resonant structure lies in the adoption of 3 design concepts:1.Ridge is added to the cut-off waveguide to enhance the coupling between resonators;2.Ridge makes the open end of the resonators achieve dielectric capacitive loading and increase power capacity;3.Q value can be increased by modifying the input/output coupling type.The rapid design of the microwave filter can be realized by the combination of the lumped parametric component mapping technique and the coupling matrix theory.A fourth-order new structure filter was designed and simulated based on the above design solutions,of which the center frequency is 10 GHz,the bandwidth is 1.2GHz,and the insertion loss is as low as 0.5d B,the excelent performance of the new structure filter is verified by this example.X-band broadband filter was proposed based on the fourth-order filter with band of 8GHz-12 GHz,the relative bandwidth of 40%,stopband extends from 12 GHz to 38 GHz,26GHz stopband width,which can effectively suppress the out-of-band harmonics.The coupling can be increased or decreased by changing the width of the ridge between resonator,and the miniaturization of the filter can be accomplished with a simulation size of 20mm*9mm*7mm by maintaining the same distance of resonators.The S-band quasi-elliptic function filter can be achieved by bending the linear filter into two rows and adding a capacitive probe to achieve the cross coupling between non-adjacent resonators,with simulation bandwidth of 2.75GHz-3.25 GHz,there is a transmission zero at each band outside the passband 100 MHz,which is symmetrical to central frequency and enables the filter has a high band selectivity;The width of stopband is 3GHz,extends from 3.25 GHz to 6.25 GHz with 30 d B attenuation,out-of-band harmonic suppression is outstanding;After a series of work such as physical processing and testing,quasi-elliptic function filter meets the design goal,the physical volume is 45mm*45mm*30mm,small and compact.