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Uses of Transmission Lines

Transmission lines are commonly used for getting either power or signals in a regulated

way from one point to another, without those signals radiating into space or becoming

otherwise coupled to other circuits where they are not wanted.

Transmission lines are normally madę uniform in cross section. One reason for making

them uniform in cross section is that if the geometry is regular all of the effects discussed

earlier become predictable without undue complexity.

As stated briefly above, a reason for the use of transmission lines, particularly of the

coaxial variety, is that they can reduce or eliminate unwanted coupling between different

parts of the Circuit. When such coupling comes about from electric fields, those electric

fields terminate on charges which remain on the outside of the outer conductor and do not

become part of the voltage or currents which are flowing on the inside. When the unwanted

coupling is via magnetic field, twin lines may be used in the twisted pair configuration so

that the magnetic flux which links a part of the Circuit is approximately cancelled by the

magnetic flux linking another part, and only smali net coupling exists.