A number of methods have been reported for the design of open-circuited interdigital lines. This paper describes a method based on the equivalent transformation of distributed lines. First, multiwire coupled lines are expressed in terms of equivalent circuit elements and simple short-circuited stubs. Using two or three equivalent transformations, cascaded high-pass distributed circuits with transformers at the input and output ports and a third-order attenuation pole at dc are obtained. Transformation from these circuits to open-circuited interdigital circuits is always possible if some redundant unit elements are allowed. By using a Z matrix, the necessary and sufficient condition to be satisfied by a high-pass distributed circuit with transformers and a third-order dc pole are investigated. The relations between the specifications and characteristics of filters and working transfer coefficients are clarified in the cases of Wagner and Chebyshev approximations. When transformers result, they are included in the open-circuited interdigital circuits. It then becomes possible to synthesize open-circuited interdigital circuits from the working attenuation basis. As an example of synthesis, a filter with Chebyshev characteristics is designed and the results are found to agree well with theory.
|Number of pages||10|
|Journal||Electron Commun Jpn|
|Publication status||Published - 1977 Jan 1|
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