New microstrip bandpass filter configuration with improved attenuation of one adjacent channel

摘要

A new topology for fourth-order microstrip bandpass filters is investigated in this paper. Compared to the classical quadruplet, the proposed new topology offers an extra coupling between two resonators, allowing this way the design of fourth order filters with two attenuation poles situated on the same side of the passband. A strongly asymmetric transfer characteristic can be obtained by a proper choice of the positions of the two attenuation poles, providing a high attenuation not only at a single frequency, but in a large adjacent frequency band, as needed in some diplexer applications.