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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



into a conducting material. This is done essentially by fabricating the con- 

 ductor of many insulated laminae or filaments of conducting material ar- 

 ranged parallel to the direction of current flow. If the transverse dimensions 

 of the laminae or filaments are small compared to the skin depth 5 at the 

 frequency under consideration, and if the velocity of the electromagnetic 

 wave along the conductor is close to a certain critical value, the wave will 

 penetrate into the composite conductor a distance great enough to include 

 a thickness of conducting material many skin depths deep. Physically speak- 

 ing, the lateral change of the wave through the conducting regions is very 

 nearly cancelled by the change through the insulating regions. 



In Fig. 1 there is shown a cross-section view of a coaxial cable with a 



Fig. 1 — Laminated transmission line. 



laminated center conductor. The center conductor is formed of a non-con- 

 ducting core surrounded by alternate layers of a conductor of thickness W 

 and conductivity a, and an insulator of thickness / and dielectric constant e. 

 The center conductor is embedded in an insulator of dielectric constant ci 

 which is in turn encased in the outer conductor. We will assume all the 

 conductors and insulators to have the permeability fio of free space. 



We will associate with the inner laminated conductor an average dielectric 

 constant^ for transverse electric fields given by 



(-?) 



(1-2) 



' A similar average dielectric constant has been considered by Tokio Sakurai, Journal 

 of Physical Society of Japan, Vol. 5, No. 6, pp. 394-398, Nov.-Dec. 1950. 



