Hollow pipes of relatively small dimensions

Summary Several cross sectional shapes for hollow-pipe transmission lines are described that provide lower operating frequencies for given outside dimensions than do the simple shapes heretofore proposed. The theory for one such line, the “septate coaxial cable” is derived, and experiments are reported. Cavity resonator embodying these principles are also described. Introduction The hollow-pipe type of conductor^1,2 for ultrahigh-frequency electromagnetic energy, although possessing several desirable features, has the disadvantage that its transverse dimensions are relatively large; namely, of magnitude comparable to the wave length. The object of this paper is to lessen this encumbrance by describing pipes that have transverse dimensions several times smaller than those of the simple forms previously proposed.^∗