The Foster Type Circuit For The H-matrix And Application to Coupled Line Filter of Even Order

The Foster-type circuit of even order is realized in a simple configuration by use of the H-matrix. The Foster-type circuit has some superior properties to those of the popular ladder networks. Conventionally, the Foster-type circuits are designed by applying the eigen-mode expansion method only to the Z matrix or the Y matrix. This process is well suited for the realization of the circuits of odd order, and hence the axial symmetrical structure is readily realized. However, in this conventional scheme it is difficult to design the Foster type circuit of even order and the axial anti-symmetrical structure, although the theoretical network synthesis itself is possible. This paper shows that the H-matrix and the G-matrix have complementary characteristics to those of the Z-matrix and the Y-matrix for the Foster-type circuit. We show that the circuit of even order and hence the axially anti-symmetrical structure is well realized by the H-matrix. To demonstrate the usage of these properties, an even order band pass filter of the Foster-type circuit is designed based on the H-matrix.