TABLE OF CONTENTS We return to our considerations of rectangular wave guides. The wave or phase velocity of the TE fundamental mode with m = l, n = 0 is (cf. Eq. (14.94) and thereafter)
The wavelength is ? = 2 ? c/ ?.
Next we consider the phase velocity in the general case, this means for
In this general case the phase velocity is
Thus the phase velocity is always larger than the velocity of light! In fact it becomes infinite at the critical frequency ? 0.
The velocity of energy transport is here in the case without attenuation, i.e. without loss of energy, the so-called group velocity. This group velocity v g is defined by
We see that the group velocity of the wave in the wave guide is always less than the velocity of light and vanishes at the critical frequency. Finally we observe that
This is again a relation which is of wider generality than our derivation here.
