Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2002-01-02
2003-09-09
Ham, Seungsook (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S172000
Reexamination Certificate
active
06617941
ABSTRACT:
BACKGROUND OF THE INVENTION
Design of a filter system with at least two longitudinal branches that have longitudinal inductors, and a filter arrangement with at least one filter section that has at least one transverse branch interposed between the longitudinal branches and at least one adjacent filter section that directly adjoins the transverse branch.
Such a filter system, which is suitable as a low-pass filter for an ADSL diplexer, is known from the “Handbook of Filter Synthesis” by Anatol I. Zverev, 1967, e.g., p. 59, FIG. 2.39.
A filter system with four connections has two longitudinal branches, which are symmetrically constructed. The filter system has a plurality of filter sections connected in series. The first filter section on the input side has one longitudinal inductor per longitudinal branch. The remaining filter sections, on the input side, each have a transverse branch comprising a capacitor interposed between two coupled transverse inductors and, on the output side, one longitudinal inductor per longitudinal branch. The longitudinal inductors and the transverse inductors of each filter section are coupled with each other, i.e., the inductors consist of windings that are wound around the same magnetic core. These magnetic cores are particularly costly. For each additional filter section, two additional magnetic cores are required. The more filter sections the filter system has, the more expensive it is.
In the older German Patent Application 198 51 872.2, to increase the return loss, each longitudinal inductor is replaced by two longitudinal inductors that are connected in series and are not coupled with each other. An electrical resistor is connected in parallel to one of the longitudinal inductors. This does not substantially change the transmission characteristics, such as group delay distortion.
SUMMARY OF THE INVENTION
The object of the invention is to define a method for designing a filter system, in which the filter system has fewer magnetic cores compared to the prior art, without changing the transmission characteristics.
Embodiments and further developments of the inventive concept are set forth in the dependent claims.
The method according to the invention for designing a filter system with at least two longitudinal branches that have longitudinal inductors, at least one filter section that is provided with at least one transverse branch interposed between the longitudinal branches, and at least one adjacent filter section, which directly adjoins the transverse branch, determines the arrangement of the inductors by means of a first type of transformation characterized by the following process sections:
First, the filter section has at least one free longitudinal inductor of the first longitudinal branch, a free longitudinal inductor of the second longitudinal branch coupled therewith and the transverse branch which consists of a capacitor that is interposed between two transverse inductors that are coupled together. The adjacent filter section first has at least one free longitudinal inductor of the first longitudinal branch and a free longitudinal inductor of the second longitudinal branch coupled therewith.
Subsequently, between the transverse branch and the adjacent filter section, a preliminary longitudinal inductor and a compensation inductor compensating the same and connected in series are inserted in each longitudinal branch. The preliminary longitudinal inductors are coupled with each other and the compensation inductors are coupled with each other.
Subsequently the compensation inductors are integrated into the free longitudinal inductors of the adjacent filter section.
Afterwards, the preliminary longitudinal inductors, the free longitudinal inductors of the filter section and the transverse inductors are replaced by four end inductors coupled with each other such that an equivalent circuit diagram of the four end inductors corresponds with the circuit diagram of the preliminary longitudinal inductors, the free longitudinal inductors of the filter section and the transverse inductors.
A second type of transformation provides for the following process sections:
First, the filter section has a longitudinal inductor of the first longitudinal branch, a longitudinal inductor of the second longitudinal branch coupled therewith and the transverse branch. The adjacent filter section first has at least one longitudinal inductor of the first longitudinal branch and a longitudinal inductor of the second longitudinal branch coupled therewith.
Subsequently, the longitudinal inductors of the filter section are each replaced by a first longitudinal inductor, which forms at least one part of the free longitudinal inductor, and a second longitudinal inductor connected in series therewith, to which a resistor R is connected in parallel. Corresponding longitudinal inductors belonging to the same filter section are coupled with each other.
Then, the preliminary longitudinal inductor and the compensation inductor are inserted.
A third type of transformation provides for the following process sections:
First, the filter section has a longitudinal inductor of the first longitudinal branch, a longitudinal inductor of the second longitudinal branch coupled therewith and the transverse branch. The adjacent filter section first has at least one longitudinal inductor of the first longitudinal branch and a longitudinal inductor of the second longitudinal branch coupled therewith. Subsequently, the longitudinal inductors of the filter section and the adjacent filter section are replaced, respectively, by a first longitudinal inductor and a second longitudinal inductor connected in series therewith, to which a resistor is connected in parallel. Corresponding longitudinal inductors that belong to the same filter section are coupled with each other.
Subsequently, the first longitudinal inductors and the second longitudinal inductors of the same filter section per longitudinal branch are replaced by a new first longitudinal inductor and a new second longitudinal inductor such that the new second longitudinal inductor is connected in series with the resistor. This series connection is connected in parallel to the new first longitudinal inductor. In the same filter section, the new first longitudinal inductors of the first longitudinal branch and the second longitudinal branch are coupled with each other and the new second longitudinal inductors of the first longitudinal branch and the second longitudinal branch are coupled with each other.
Afterwards, in each longitudinal branch of the filter section, an additional preliminary longitudinal inductor and an additional compensation inductor compensating the same and forming at least a portion of the free longitudinal inductor are inserted between the parallel connection of the new first longitudinal inductor to the series connection and the adjacent filter section.
Thereafter, the additional preliminary longitudinal inductors, the new first longitudinal inductors which form an additional circuit diagram, are replaced by four longitudinal end inductors that are coupled with each other, such that an equivalent circuit diagram of the four longitudinal end inductors corresponds with the additional circuit diagram.
Then, the preliminary longitudinal inductor and the compensation inductor are inserted.
A further embodiment of the invention provides for a method in which a first capacitor electrode of the capacitor is connected with a first end inductor that is connected with the adjacent filter section and with a second end inductor,
in which the winding direction of the first inductor relative to the capacitor corresponds with the winding direction of the second end inductor relative to the capacitor,
in which a second capacitor electrode of the capacitor is connected with a third end inductor that is connected with the adjacent filter section and with, a fourth end inductor,
in which the winding direction of the first end inductor relative to the capacitor is opposite to the winding direction of the third end inductor relative to
Ham Seungsook
Kilpatrick & Stockton LLP
Russell Dean W.
Vacuumschmelze GmbH & Co. KG
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