The characteristic impedance of finlines with up to three slots is calculated by a rigorous hybrid-mode analysis which includes the finite metallization thickness and finite depth of the mounting grooves. The transverse resonance principle utifiied reduces considerably the order of the involved matrix eigenvalue problem. The propagation constants for the fundamental HE~mode (and EHO mode at related structures), as well as for the higher order modes (up to HE,), and the characteristic impedances

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... for the fundamental modes are computed as a function of freqnency for the bilateral and unilateral fhdine, as well as for the unilateral finline with two coupled slots, and an additional slot on the opposite side of the substrate surface. The finite metaflization thickness and mounting groove depth considered show significant influence on the behavior of the characteristic impedance.