How We Will Proceed In the early chapters we will focus on the behaviour of transmission lines which will be
frequently of the twin line or coaxial line structure. The lines are usually uniform in
cross section with respect to the longitudinal direction. Magnetic fields will usually be
completely transverse, and a distributed circuit treatment will be possible.
An important property of the transmission lines is that once you take into account
the effects of distributed circuit theory, the current and voltage at one end of the line is
seen to be not the same as the current and voltage at the other. Clearly in this context
the wires of transmission line are not behaving as the conductors of a lumped circuit in
which the potential has the same value all the way along the wire (except for the effect of
resistance) and the current entering one end of the wire is the same as the current leaving.
Later in chapters 8 to 11 we will have to consider more complex geometries for signal
transmission, in which situations magnetic fields in a longitudial direction make it
necessary for us to use a more general treatment based upon electromagnetic field theory.
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