radio frequencies from 300 megahertz (MHz) to 300 gigahertz (GHz). The microwave region of the spectrum thus includes decimeter, centimeter, and millimeter waves (seeRADIO WAVE). In English, the term “microwave” is sometimes used in a narrower sense; for example, the microwave region may be taken as extending from 1 GHz to 300 GHz or from 300 MHz to 30 GHz.
Microwave frequencies are used mainly in radar, radio communication, and radio-frequency spectroscopy. In order to make practical use of the microwave region, it was necessary to create oscillators and amplifiers based on new principles—for example, magnetrons, klystrons, and traveling-wave tubes. Microwave wave guides and special types of antennas were created to channel microwaves. The technology of microwaves is the subject of microwave engineering.