Multi-Band Bandpass Microstrip Filters Based on Two Codirectional Hairpin Resonators

In this paper, we study the frequency properties of structures based on two multistep codirectional hairpin resonators, which provide the possibility to realize one-, two-, tri-, and four-band filters under certain conditions. The authors show that these two-resonator filters have increased frequency selectivity due to the formation by them of a significant number of working attenuation poles, which are four times greater than the number of resonators in the filter. For these structures, topological differences are determined, and the mechanisms of formation of their frequency characteristics are studied. The article shows that the considered two-resonator structures combine compactness, increased frequency selectivity, and reduced loss level.