UHF-Band High Performance Tunable Bandpass Filter Technical Research

The UHF band for mobile communications,the main frequency can electronic tuning of the frequency band filter can realize the efficient utilization of spectrum resources and improve the system,the compatibility between the electrically tuned filter at the same time has the characteristics of the "flexible" very adapt to the requirement of modern communication,has become one of the important task to filter research.HTS filter has low insertion loss,high degree of restraint outside the band's unique advantages,but its work on the essential condition of refrigeration environment make the price lower and greatly limits its application scope,the use of electronic tuning way makes a single superconducting filter can work at different frequencies is expand application field of superconducting technology is an important means.This paper proposes the use of piezoelectric ceramic filter electrically adjustable tuning method,using the tuning method implements a UHF band high-temperature superconductivity bandpass filter,which has small volume,good reconfigurable,low insertion loss and high degree of restraint outside the band edge,can greatly reduce the cost of superconducting technology,has important application significance.The main research work of this paper is summarized as follows:1.Based on the research status of tunable filter,the cut-off waveguide band-pass filter has good electromagnetic shielding performance and high power capacity,which solves the problem of large insertion loss and low power capacity of planar structure filter;combined with cut-off waveguide characteristics and capacitance;The theory of loading transmission line shortening solves the problem of large volume of the cavity filter in the low frequency band,and realizes miniaturization of the device;2.Based on the characteristics of high-temperature superconducting materials,the high-temperature superconducting tape is loaded in the cavity of the cut-off waveguide band-pass filter to improve the quality factor of the cavity and reduce the insertion loss of the filter;The surface of the superconducting tape is selected by mirror image method.The resistor is tested to provide the necessary parameters for the filter design;3.Based on the filter design index and the network parameter design of the cut-off waveguide bandpass filter,the initial data of the filter is obtained,and the cavity model and feed coupling mode are optimized by HFSS simulation software,and optimized,and finally the design is satisfied.A filter model of the indicator to determine the size of each structure of the filter;4.Based on the law that the central frequency of the filter obtained by simulation changes with the size of the structure,it is proposed to use piezoelectric ceramic plates to complete the design of the electric tuning device,and realize the electric tuning of the cavity filter without sacrificing the system power capacity.5.The physical processing and assembly of the filter was completed,and the filter was tested.The filter size is 5.84 cm × 2.87 cm × 1.92 cm,which is 1/9 of the size of the traditional waveguide filter under the same index;It can be quickly tuned,the center frequency can be electrically adjusted from 1.746 to 1.894 GHz,and the bandwidth within the adjustable range is at 15 MHz,the passband interpolation loss is less than 0.6dB,and the filter stopband width is up to 6 octaves.