Investigation of the coupling coefficients of stripline resonators in combline filters on a suspended substrate

Expressions for the frequency-dependent coupling coefficients of codirectional resonators used in a miniature design of a stripline filter on a suspended substrate are derived. The obtained expressions fully reflect the specific features of the frequency response of the analyzed structure. It is shown that the numerical analysis of a 1D model of this device performed in the quasi-static approximation provides sufficiently good agreement with experimental results. The influence of the design parameters of the analyzed structure on the frequency-selective properties of band-pass filters designed on the basis of this structure is theoretically investigated, and the capabilities for a substantial improvement of the selectivity of such devices are demonstrated.