A Trisection Filter Design With Negative Slope of Frequency-Dependent Crosscoupling Implemented in Substrate Integrated Waveguide (SIW)

This letter reports on a novel realization of a microwave bandpass filter in a triplet configuration with a frequency-dependent crosscoupling implemented in substrate integrated waveguide (SIW). The design involves implementing dispersive coupling with a negative slope, a feature that allows the capabilities of the classic triplet topology to be extended. In this particular case, the implementation of two transmission zeros on the upper stopband is considered. The dispersive coupling with negative slope in SIW is achieved with a coupling with a positive slope whose sign is inverted using balanced line theory. The filter was fabricated in SIW technology, and good agreement was achieved between the simulated results and those measured.