The Design Of Tunable Band-stop Filter

With the development of communication technology,radio frequency systems have put forward many higher requirements for frequency band selectivity.In order to make each system work in the appropriate frequency band,it is important for the selectivity of the filter to the frequency band.Band stop filter is one of the key components of frequency band selection in communication system,which can filter out interference signals.The tunable band stop filter can switch the center frequency of the stop band according to actual needs,which has strong practicability and can save space and cost.After decades of research on tunable band stop filters,although significant progress has been made,there are still many shortcomings.The main disadvantages are that the frequency tuning range of the tunable band stop filter is too small,the stop band suppression is not enough,the insertion loss is too large,the tuning method is complicated,and so on.In this paper,starting from the design theory of band-stop filter,the tunable band stop filter is deeply studied,and three different types of tunable band-stop filter are designed.The first type uses a variable capacitor to load the coaxial cavity and design two narrow-band tunable cavity band-stop filters with the center frequency of the stopband in the tunable range of 1GHz-2GHz and 2GHz-4GHz.The filter's 3d B stopband bandwidth is less than 2%,and the stop-band suppression is above 30 d B.The actual production and debugging have been completed.The second type uses a step impedance resonator to design a tunable cavity band stop filter with the center frequency of the stopband in the tunable range of 1.00GHz-1.40 GHz.The filter's 3d B stopband bandwidth is close to 660-680 MHz,and the stopband suppression is greater than 60 d B.The third type uses a combination of varactor diodes and microstrip lines to design an ESC band stop filter with a tunable stopband center frequency ranging from 2.75GHz-2.90 GHz.The filter's 3d B stopband bandwidth is less than 2%,and the stopband suppression is above 15 d B.These three different filters have the characteristics of wide tuning frequency range,high stopband suppression,and convenient tuning,which can meet different needs.