reflected from one wall. The reflected energy returns to the point where it
was applied and is completely reflected again. These reflections continue
for a period of time; so we say the cavity is oscillating.
b. Now, if we terminate a resonant cavity in its characteristic
impedance, the energy applied will be absorbed by the load, and there won't
This is exactly what we do with
The fields in a waveguide, however, are not in the same
positions as they are in a resonant cavity. Look at Figure 110.
The E and H Fields Inside a Resonant
Cavity and a Waveguide.
c. Part A of Figure 110 shows a resonant cavity with its E and H
fields. Part B of Figure 110 shows a length of waveguide with its E and H
fields. Notice that the fields in the waveguide are in-phase, but those in
a resonant cavity are 90 degrees out-of-phase with each other.
d. Both illustrations in Figure 110 show the fields at one instant of
time. Figure 111 shows the field one-half cycle later.