Influence of the frequency dispersion of resonators’ coupling coefficients on the accuracy of direct-synthesis formulas for microwave filters

For the case of a wideband filter designed on the basis of parallel oscillatory circuits with combined coupling, the influence of the slope of the frequency characteristics of the coupling coefficients in a tuned filter on the values of these coefficients at the resonant frequency is investigated. The slope angle of these curves is controlled by the ratio of the inductive and capacitive components of the coupling coefficients. The actual values of the coupling coefficients are compared with the values obtained from the direct-synthesis formulas.