A Study of the Phase and Filter Properties of Arrays of Parallel Conductors between Ground Planes

A number of structures are analyzed which consist of arrays of parallel conductors between ground planes or above a single ground plane. These include interdigital line, meander line, a form of helix, "hairpin line," and reactively-loaded comb line. Equations are derived for determining the phase function Ψ per section of line in terms of voltage coupling factors K
_1n
which are obtained from the static capacitances per unit length of the conductors. Equations for the image impedance of finite arrays are obtained for three of the five cases considered. Data for computing coupling factors are presented for arrays using small wires between ground planes and for arrays having conductor dimensions such that fringing capacitance beyond nearest neighbors can be neglected. Phase characteristics for given coupling factors are presented for the various types of structures considered. These results indicate that certain of the structures have special merit for use as filters, or as slow-wave structures. An interdigital-line filter using ten conductors was constructed and found to have excellent band-pass filter characteristics and a bandwidth which is in very good agreement with the theory.