Design Procedure of a Microstrip Filter Facilitated by Lumped-Element Equivalent Circuit Representation

In this paper, a lumped-element equivalent circuit is derived for representing a microstrip filter so that the physical mechanism of the latter is expounded. If conventional filter synthesis technique is used to synthesize this equivalent circuit, the electric parameters or structural parameters of the microstrip filter can be determined by virtue of equivalence relationship from the lumped-element values. The analysis shows that the latter is capable of realizing a third-order quasi-Elliptic bandpass response. The response has two transmission zeros adjacent to its passband, which effectively improve frequency selectivity. The design procedure is summarized to facilitate its practical use. Finally, an example is presented for demonstration.