Microwaves are electromagnetic waves with a wavelength longer than infrared light, but shorter than radio waves.

Microwaves, also known as Super High Frequency (SHF) signals, have wavelengths approximately in the range of 30 cm (1 GHz) to 1 mm (300 GHz). However, the boundaries between far infrared light, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. Microwaves were discovered by James Clerk Maxwell in 1864.

Note: above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque to higher frequencies of electromagnetic radiation, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.

Uses

A microwave oven uses a magnetron microwave generator to produce microwaves at a frequency of approximately 2.4 GHz for the purpose of cooking food. Microwaves cook food by causing molecules of water and other compounds to vibrate. The vibration creates heat which warms the food. Since organic matter is made up primarily of water, food is easily cooked by this method.

A maser is a device similar to a laser, except that it works at microwave frequencies. Microwaves are also used in satellite transmissions because this frequency passes easily through the earth's atmosphere with less interference than higher wavelengths.

Radar also uses microwave radiation to detect the range, speed, and other characteristics of remote objects.

Wireless LAN communication protocols such as IEEE 802.11 and bluetooth also use microwaves in the 2.4 GHz ISM band, although some variants use a 5 GHz band for communication.

Cable TV and Internet access on coax cable as well as broadcast television use some of the lower microwave frequencies.

Microwaves can be used to transmit power over long distances, and post-World War II research was done to examine possibilities. NASA worked in the 1970s and early 1980s to research the possibilties of using Solar Power Satellite (SPS) systems with large solar arrays that would beam power down to the Earth's survace via microwaves.

The microwave spectrum is defined as electromagnetic energy ranging from approximately 300 MHz to 1000 GHz in frequency. Most common applications are within the 1 to 40 GHz range.

Microwave Frequency Bands are defined below:

 Letter Designation     Frequency Range

    L Band              1 to 2 GHz
    S Band              2 to 4 GHz
    C Band              4 to 8 GHz
    X Band              8 to 12 GHz
    Ku                  12 to 18 GHz
    K Band              18 to 26 GHz
    Ka                  26 to 40 GHz
    Q Band              30 to 50 GHz
    U Band              40 to 60 GHz
    V Band              46 to 56 GHz
    W Band              56 to 100 GHz
For some of the history in the development of electromagnetic theory applicable to modern microwave applications see the following figures: Michael Faraday, James Clerk Maxwell, Heinrich Hertz, Guglielmo Marconi, Samuel Morse, Sir William Thomson later Lord Kelvin, Oliver Heaviside, Lord Rayleigh, Oliver Lodge.

Microwave specific work:

  • Barkhausen and Kurz - Positive grid oscillators
  • Hull - Smooth bore magnetron
  • Varian Brothers - Velocity modulated electron beam --> klystron tube
  • Randall and Boot - Cavity magnetron

See also: