Combined microstrip and suspended substrate stripline combline bandpass filter with two transmission zeros

A novel Structure of a narrowband combline bandpass filter with two transmission zeros is introduced. It is composed of two different physical resonator structures which are the microstrip and the suspended substrate stripline on a single layer substrate. The simulated in-band insertion loss is low due to four high-Q stripline resonators, while the transmission zeros are implemented with two microstrip resonators to enhance the selectivity and facilitate the integration of the filter with other system parts. The passband is from 3.41 to 3.48 GHz with a small fractional bandwidth of 2%. Preliminary experimental results are presented to validate the design concept.