Research On Miniaturized Wide Stop-band Waveguide Filter

Microwave filter is a very important component of communication system and radar system.The filter can pass through the required frequency band of the system signal and effectively suppress the interference signal.Microwave filters often have the characteristics of miniaturization,wide stop-band,low insertion loss,high frequency selectivity and high power capacity.Waveguide filter is widely used in satellite communication system because of its low insertion loss and high power capacity.However,the traditional waveguide band-pass filter is not ideal due to it's out of band suppression characteristics.In system applications,the low-pass filter structure is often used to replace the band-pass filter function.The narrow edge reduction technology and high filter order in the waveguide low-pass filter make the filter volume larger.In this paper,the miniaturization and wide stop-band characteristics of metal waveguide band-pass filter are studied theoretically and experimentally,and the miniaturization filter of dielectric waveguide structure is also simulated.Based on the direct coupled waveguide filter,this dissertation proposes a new technology of transverse uniform capacitive diaphragm loading and heterodyne tuning of out of band transmission poles in the resonator,which realizes the miniaturization and wide stop-band characteristics of the waveguide filter.Taking the X-band waveguide band-pass filter as an example,the filter parameters are:the center frequency is 9.2GHz,and the bandwidth is 400MHz.The theoretical calculation and practical processing of half-wavelength direct coupled waveguide filter,capacitive-loaded filter and capacitive-loaded combined out-of-band poles control filter are carried out respectively.The simulation and experimental tests show that the total length of the capacitive loaded combined pole control filter is reduced to 42%of the direct coupled waveguide filter,and the 40 dB stop-band suppression system bandwidth exceeds the fourth harmonic(TE₄₀ mode).The experimental results of the small signal parameters of the filter are basically consistent with the simulation results,which verifies the feasibility of the miniaturization and wide stop-band design method proposed in this paper;and the filter with similar technical ideas has been applied in a space system.Finally,aiming at the demand of miniaturized filter in 5G communication application,this paper studies the miniaturized filter filled with high dielectric constant media,and designs a folded dielectric waveguide filter by simulation.The overall volume of the dielectric filter can be reduced to 0.1%of the volume of traditional waveguide structured filter with the same order.