Upon closure of a switch, the TEM wave
(step) travels at the speed of light between the conducting wires of the transmission line, from battery to load, as depicted in Fig.
Ando, "Single-layer feed waveguide consisting of posts for plane TEM wave
excitation in parallel plates," IEEE Trans.
In the studies mentioned above the authors consider the excitation of the fundamental TEM wave
which has no dispersion in the biconical line.
This situation is similar to the TEM wave
incident normally to the planar boundary .
It can support true TEM wave
propagation and is capable of extremely wideband frequency performance.
Since a coaxial waveguide is used, a TEM wave
is propagating inside the waveguide.
As well-known from electromagnetic field theory, the propagation along such a medium can be described in circuital terms as the propagation of a TEM wave
along a cascade of transmission line segments (see Figure 1(b)), whose key parameters are the characteristic impedances Z and the propagation constants [beta] .
We can get a decent estimate of this impedance by using the radial TEM wave
concepts described previously.
field components pertaining to the fundamental TEM wave
and to the higher order modes.
This is not strictly valid since the waveguide does not propagate a TEM wave
, but nevertheless yields fairly good results.
For example, if the requirement is to design a miniature 20 dB wideband coupler, stripline technique may be chosen, shown in Figure 2, as it provides a miniature size and pure TEM wave
with no dispersion.
The electric field component can be derived from a linear superposition of the TEM wave
and an oscillating magnetic dipole at the end of the conductor.