Portal:Physics/Selected article/April 2008

Microwaves are electromagnetic waves with wavelengths between one meter and one millimeter, or with frequencies between 300 megahertz and 300 gigahertz.

Apparatuses and techniques may be described qualitatively as "microwave" when the wavelengths of signals are roughly the same as the dimensions of the equipment, so that lumped-element circuit theory is inaccurate. As a consequence, devices that utilize microwaves, such as the microwave communications tower pictured, tend to move away from the discrete resistors, capacitors, and inductors used with lower frequency radio waves. Open-wire and coaxial transmission lines give way to waveguides, and lumped-element tuned circuits are replaced by cavity resonators or resonant lines. Similarly to visible light, the phenomena of reflection, polarization, scattering, diffraction, and atmospheric absorption are observed in microwaves.

Microwaves were first theorized in 1864 by James Clerk Maxwell, and were later detected in the 1940s by Sir John Randall and Dr Harry Boot. Since then, microwaves have been used in communication, remote sensing of both earth based and astronomical bodies, food preparation, and non lethal weaponry.