Figure 1: Cutaway view of a waveguide termination
Waveguide terminations (dummy loads) are an important protective component in a system of line-based energy transmission. It is a resistive load that is matched to the characteristic impedance of the waveguide to prevent the origin of standing waves.
If the energy transported in the waveguide is not to be radiated into the free space at the end of the waveguide, the waveguide must be loaded with a component working as an effective resistor. This is usually a waveguide section that is several wavelengths long and is filled with damping material, for example with a mixture of sand and graphite. This material can also be distributed in steps to reduce reflections. If the fields enter the damping material, currents flow and the energy is converted into heat.
In order to dissipate this heat, the waveguide termination must be cooled well. This cooling can be done by air, but also by water or oil cooling. Oil cooling has the advantage over water cooling that the oil can withstand higher temperatures without evaporating.