Highly Selective Microstrip Filters Based on Three-Resonator Structures

Using three-resonator structures as an example, the constructing principles of highly selective microstrip filters with a significantly limited number of resonators are being researched. The base element of such filters is a multi-step quarter-wave lattice section, in which three working attenuation poles are formed. Three-resonator filters contain two such electromagnetically interacting lattice sections, which ensures the formation of up to eight working attenuation poles in the structure. The formation mechanisms of working attenuation poles in three-resonator structures of various designs have been researched and a comparative analysis of their characteristics with the characteristics of traditional four-resonator filters with parallel energy transfer paths, in which only three working attenuation poles are realized, has been performed. Three-resonator structures using multi-step lattice sections have increased frequency selectivity and provide discharge of the spectrum of parasitic passbands is shown