Research On Wide Stopband Characteristics Of Waveguide Bandpass Filter

In satellite communication,the filter is an indispensable part of the communication link.From satellite transmitting station,high power signal pulse,even all kinds of space signal can cause interference to the satellite communication,or even directly interrupt.With the development trend of miniaturization and integration of communication equipment,wide stopband,high power and miniaturization have become the urgent needs of the research and development of filters.Waveguide bandpass filters are widely used in spaceborne microwave communication systems because of their high power capacity and low insertion loss.However,due to the multi-mode resonance characteristic of rectangular resonator,a large number of higher order modes are generated in traditional waveguide filters,which is the main cause of parasitic passband excitation of the filters.From the point of view of system application,the anti-EMI ability of the filter is greatly reduced.Firstly,the paper introduces the design principle and background of the filter,and analyzes the causes of the parasitic passband through the theoretical derivation and electromagnetic simulation.The suppression methods of parasitic passband,such as capacitor loading,changing the width of the filter,and capacitor loading and changing the combination of the width of the filter,are proposed,and the design verification is carried out.Finally,by adding a pair of capacitive diaphragms in the middle of the resonator and changing the wide and narrow edges,the poles out of the band are tuned to achieve the wide stopband suppression,and an X-band ultra-wide stopband bandpass filter is designed.The technical specifications of the filter design are as follows: center frequency is 9.5GHz,bandwidth is 400 MHz,40dB stopband width reaches 37 GHz,and band insertion loss is less than 0.5dB.Theoretical simulation and actual processing test show that the volume of the filter designed in this paper is reduced sharply,and 54% less than that of the Chebyshev filter prototype,which better meets the development trend of miniaturization and lightweight of the whole machine.In particular,the wide stopband method proposed in this paper can greatly expand the stopband bandwidth of the waveguide filter,and the stopband suppression bandwidth of the 40 dB filter reaches 5.7times the waveguide cutoff frequency.The ultra wide stopband can restrain the electromagnetic interference of the microwave receiver better and improve the EMC performance of the system.