As shown in the given diagram the saw filter consists of a piece of quartz crystal material on the surface of which the metallic fingers are engraved. One pair of metallic figures is used for the input and the other pair is used for filtered output.
When the wide band of microwave length of frequencies is applied at the input of the saw filter, the crystal particles starts to vibrate. The frequency of its vibration or the output frequency depends upon the distance between the figures.
This vibration of the crystal particles at the input transfers towards the output figures. There the vibration of crystal particles results to induced voltage in the output metallic figure.
The frequency of the output figures will be the desired frequency selected by the design of the filter device. Saw stands for surface acoustic waves which are the principal of the saw filter.