Electronically Adjustable Common Mode Rejection Filter Based on Frequency Selective Coupling

Abstract

The invention discloses an electrically adjusting common mode rejection filter based on selective frequency coupling. The electrically adjusting common mode rejection filter based on selective frequency coupling comprises an upper-layer microstrip structure, loading capacitors, loading variable capacitance diodes, a dielectric substrate and a bottom-layer metal ground plate, wherein the upper-layer microstrip structure is attached to the upper surface of the dielectric substrate, and the lower surface of the dielectric substrate is provided with the bottom-layer metal ground plate; the upper microstrip structure is composed of four half-wavelength resonators, four feeder lines and four ports; both ends of every feeder line form symmetric coupling with both ends of the corresponding half-wavelength resonator; every port is formed in the middle of every feeder line; the loading variable capacitance diodes are arranged at the open ends of the half-wavelength resonators for adjusting the central frequency; the loading capacitors are arranged at the tail ends of the feeder lines and the connecting positions among the feeder lines for controlling external quality factors.

Description

technical field [0001] The invention relates to an electric-tunable common-mode suppression filter, in particular to an electric-tunable common-mode suppression filter based on frequency selective coupling that can be applied to a radio frequency front-end circuit. Background technique [0002] In existing wireless communication systems, common mode rejection filters are in great demand because they have good anti-interference ability against environmental noise. In recent years, scholars at home and abroad have launched a lot of research to design such filters. Some people use an S-shaped resonant ring on the floor of the microstrip structure to suppress common-mode signals. Such a filter circuit can suppress common-mode signals without adding an external circuit structure, but it will generate relatively large losses, and at the same time The suppression effect of common-mode signals is not very good; in addition, a more common way is to design some special circuit struct...

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Problems solved by technology

However, these two methods suppress the common-mode signal by controlling the resonator. So far, there is no publicly proposed electronically tuned filter that suppresses the common-mode signal by controlling the feed structure.

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