A Tunable Filter with Stable Wide Stopband

Abstract

The invention discloses an adjustable filter with a stable wide stop band, which solves the technical problem that in the prior art, an upper stop band is not stable enough as the harmonic frequency links along with a fundamental wave passband when the filter is designed. The adjustable filter with the stable wide stop band primarily comprises two phase step impedance resonators (SIR) which separately load varactors Cv11 and Cv12, a pair of feeders and two varactors Cv21 and Cv22 connected to the resonators and the feeders, wherein the varactors Cv11 and Cv12 loaded to zero points of the spread voltages of the lowest subharmonic (third harmonic) radio frequency are used for adjusting the fundamental frequency and meanwhile, the third harmonic frequency does not link and tune along with fundamental frequency, so that the stable distance between the fundamental waves and the harmonic waves is stable. The adjustable filter optimizes the characteristic parameters of SIR on the premise of stabilizing the upper stop band, so that the frequency tuning range of the fundamental wave passband is expanded, and the performance index can meet the application demand of microwave frequency band.

Description

Technical field [0001] The invention relates to the technical field of radio frequency communication, and in particular to a tunable filter with a stable and wide stop band. Background technique [0002] With the rapid development of wireless communication technology, reconfigurable / tunable microwave components are highly concerned by scholars. As an important frequency selection component, tunable band-pass filter has been widely studied because of its advantages in reducing system size, cost and complexity. In the past period of time, a variety of frequency tuning techniques such as microelectromechanical systems, ferroelectrics, piezoelectric actuators, varactor diodes, and microfluidics have been used to study tunable filters. However, filters based on flat transmission lines (such as microstrips) loaded with varactors have the advantages of small size, fast tuning speed and low cost in use, and are popular in the design of tunable filters. [0003] In recent years, most tuna...

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Problems solved by technology

[0003] In recent years, most tunable filters load a varactor diode to the open end of a quarter-wavelength (λ / 4) uniform impedance resonator (UIR) or stepped impedance resonator (SIR) for analysis to obtain the maximum frequency However, the tunable filter with this structure does not take into account that its harmonic frequency will be linked with the fundamental passband, which will cause the problem that the upper stopband is not stable enough, so it cannot meet the diverse wireless communication needs.

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