Balanced filter using improved coupling feed line

Abstract

The invention discloses a balanced filter using an improved coupling feed line. The balanced filter comprises input and output ports and two cascaded improved coupling feed lines. One improved coupling feed line comprises a first coupling transmission line, a second coupling transmission line and a first branch knot loaded between the first coupling transmission line and the second coupling transmission line, wherein the first coupling transmission line and the second coupling transmission line are symmetrically distributed. The other improved coupling feed line comprises a third coupling transmission line, a fourth coupling transmission line, a second branch knot, a third branch knot, a fourth branch knot and a fifth branch knot, wherein the third coupling transmission line and the fourth coupling transmission line are symmetrically distributed; the second branch knot, the third branch knot, the fourth branch knot and the fifth branch knot are loaded between the third coupling transmission line and the fourth coupling transmission line. The first coupling transmission line, the second coupling transmission line, the third coupling transmission line and the fourth coupling transmission line are connected to one input and output port respectively. Each input and output port is loaded with a coupling branch knot which is used for introducing a transmission zero point. By using the filter of the invention, because of common mode rejection of the filter itself, a differential mode and a common mode can be designed separately and the common mode rejection can be obviously improved.

Description

technical field [0001] The invention relates to the technical field of microwave communication, in particular to a balanced filter using an improved coupling feeder. Background technique [0002] Balanced filters have attracted more and more attention since they were proposed, and there are different structures to meet different needs. However, the design methods are basically based on the comprehensive design of band-stop filters and band-pass filters. The design is more complicated, and it is difficult to achieve high selectivity and high common-mode rejection at the same time. Therefore, it is becoming more and more important to study novel common-mode suppression structures. [0003] On the other hand, coupled lines are often used in the design of filters, but traditional coupled feeders transmit common-mode signals as well as differential-mode signals. The coupled feeder itself does not suppress the common-mode signal of the filter, so additional measures need to be t...

AI Technical Summary

Problems solved by technology

[0009] The purpose of the present invention is to overcome the deficiencies in the prior art, provide a balanced filter using an improved coupling feeder, overcome the difficulties of simultaneous realization of high selectivity and high common-mode rejection of the balanced filter, and realize common-mode rejection at the feeder end, Make the design of the filter focus on the realization of the differential mode passband; overcome the problem of flat passband selectivity of the existing balanced filter, provide a new type of short-circuit coupling stub loading with multiple transmission zeros; overcome the high frequency resistance of the differential mode of the balanced filter To solve the problem of difficult band control, provide a wide stop band implementation with harmonic suppression

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