The Variable Attenuator is a device used to reduce the power level at the input of microwave components. It is of the side vane type. A plastic fiberglass blade with a resistive coating is used to produce attenuation. The blade is inserted vertically into the waveguide, parallel to the short side walls.

The attenuation produced by the attenuator depends on the position of the blade in the waveguide. The blade position can be changed by using the attenuator's micrometer. The attenuation increases as the blade is moved towards the center of the waveguide.