Editing Waveguide (section)

{{Short description|Structure that guides waves efficiently}}
{{use mdy dates|date=October 2022}}

[[File:WaveguideJ-Band.png|thumb|An example of a waveguide: A section of flexible waveguide used for [[RADAR]] that has a [[waveguide flange|flange]].]]

[[File:Waveguide x EM rect TE31.gif|thumb|right|alt=(animation) Electric field Ex component of the TE31 mode inside an x-band hollow metal waveguide. A cross-section of the waveguide allows a view of the field inside.|Electric field Ex component of the TE31 mode inside an x-band hollow metal waveguide.]]

A '''waveguide''' is a structure that guides waves by restricting the transmission of energy to one direction. Common types of waveguides include [[acoustic waveguide]]s which direct [[sound]], [[optical waveguide]]s which direct [[light]], and [[radio-frequency waveguide]]s which direct [[electromagnetic wave]]s other than light like [[radio wave]]s.

Without the physical constraint of a waveguide, waves would expand into three-dimensional space and their intensities would decrease according to the [[inverse square law]].

There are different types of waveguides for different types of waves. The original and most common meaning is a hollow conductive metal pipe used to carry high frequency [[radio wave]]s, particularly [[microwave]]s.{{sfn|Institute of Electrical and Electronics|Radatz|Standards Coordinating Committee|IEEE Computer Society|1997}}  [[Dielectric waveguide]]s are used at higher radio frequencies, and transparent dielectric waveguides and [[optical fiber]]s serve as waveguides for light.   In [[acoustics]], air ducts and [[Horn (acoustic)|horn]]s are used as waveguides for sound in musical instruments and [[loudspeaker]]s, and specially-shaped metal rods conduct ultrasonic waves in [[ultrasonic machining]].

The geometry of a waveguide reflects its function; in addition to more common types that channel the wave in one dimension, there are two-dimensional slab waveguides which confine waves to two dimensions.   The frequency of the transmitted wave also dictates the size of a waveguide: each waveguide has a [[cutoff wavelength]] determined by its size and will not conduct waves of greater wavelength; an [[optical fiber]] that guides [[light]] will not transmit [[microwaves]] which have a much larger wavelength. Some naturally occurring structures can also act as waveguides. The [[SOFAR channel]] layer in the ocean can guide the sound of [[whale sound|whale song]] across enormous distances.{{sfn|Payne|Webb|1971}}
Any shape of cross section of waveguide can support EM waves. Irregular shapes are difficult to analyse. Commonly used waveguides are rectangular and circular in shape.