Jupiter missions could also help search for dark matter

In a recent study published in the Journal of High Energy Physics, two researchers from Brown University demonstrated how data from past missions to Jupiter can help scientists examine dark matter, one of the most mysterious ...

Chiral sources for metamaterial interface waveguides

Metamaterial interface waveguides can confine and guide electromagnetic (EM) waves, which has attractive potential in integrated photonics physics and wireless devices, from radio frequencies to optical bands. The energy ...

Astronomers are helping find elusive atoms across the universe

Astronomers at the University of Toronto have spotted some of the most elusive stuff in our universe by taking a deep look at the cosmic web, the network of filaments and knots that trace the large-scale distribution of galaxies.

A massive galaxy supercluster in the early universe

The structure of the universe is often described as being a cosmic web of filaments, nodes, and voids, with the nodes being clusters of galaxies, the largest gravitationally bound objects known. These nodes are thought to ...

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Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz. This broad definition includes both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often putting the lower boundary at 1 GHz (30 cm), and the upper around 100 GHz (3 mm).

Apparatus 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, practical microwave technique tends to move away from the discrete resistors, capacitors, and inductors used with lower-frequency radio waves. Instead, distributed circuit elements and transmission-line theory are more useful methods for design and analysis. Open-wire and coaxial transmission lines give way to waveguides and stripline, and lumped-element tuned circuits are replaced by cavity resonators or resonant lines. Effects of reflection, polarization, scattering, diffraction, and atmospheric absorption usually associated with visible light are of practical significance in the study of microwave propagation. The same equations of electromagnetic theory apply at all frequencies.

The prefix "micro-" in "microwave" is not meant to suggest a wavelength in the micrometer range. It indicates that microwaves are "small" compared to waves used in typical radio broadcasting, in that they have shorter wavelengths. The boundaries between far infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study.

Electromagnetic waves longer (lower frequency) than microwaves are called "radio waves". Electromagnetic radiation with shorter wavelengths may be called "millimeter waves", terahertz radiation or even T-rays. Definitions differ for millimeter wave band, which the IEEE defines as 110 GHz to 300 GHz.

Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that it is in effect opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.

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