Selective properties of ladder-type microstrip filters on the basis of irregular resonators

Selective properties of ladder-type microstrip filters on the basis of resonators with stepwise variation of the width of a microstrip dumbbell conductor are studied in the quasi-static approximation. Designs with from three to six sections, in which the regions of coupling of neighboring resonators are determined by the length of their external low-resistivity regions, are considered. Dependences of the gain slope on the length of the resonators coupling regions and other design parameters for a fixed relative passband width are obtained. It is shown that a symmetric amplitude-frequency characteristic can be attained only by connecting the filter to transmission lines in the big diagonal. A good agreement between calculations and the experiment is observed both for open and screened designs.