2  Microwaves
Microwaves (short-wavelength radio waves), with frequencies in the
gigahertz (GHz) range, are produced by special vacuum tubes (called
klystrons, magnetrons and Gunn diodes) Due to their short wavelengths,
they are suitable for the radar systems used in aircraft navigation Radar
also provides the basis for the speed guns used to time fast balls, tennis-
serves, and automobiles Microwave ovens are an interesting domestic
application of these waves