Editing Waveguide (section)

== History ==
{{Duplication|section=yes|dupe=Waveguide (electromagnetism)#History|date=November 2020}}
The first structure for guiding waves was proposed by [[J. J. Thomson]] in 1893, and was first experimentally tested by [[Oliver Lodge]] in 1894. The first mathematical analysis of electromagnetic waves in a metal cylinder was performed by [[John Strutt, 3rd Baron Rayleigh|Lord Rayleigh]] in 1897.{{sfn|McLachlan|1964}}{{rp|8}}  For sound waves, Lord Rayleigh published a full mathematical analysis of [[propagation mode]]s in his seminal work, "The Theory of Sound".{{sfn|Rayleigh|1894}}  [[Jagadish Chandra Bose]] researched [[Extremely high frequency|millimeter]] wavelengths using waveguides, and in 1897 described to the Royal Institution in London his research carried out in Kolkata.{{sfn|Emerson|1997a}}{{sfn|Emerson|1997b|loc=[https://www.cv.nrao.edu/~demerson/bose/bose.pdf  Reprint]}}

The study of dielectric waveguides (such as optical fibers, see below) began as early as the 1920s, by several people, most famous of which are Rayleigh, [[Arnold Sommerfeld|Sommerfeld]] and [[Peter Debye|Debye]].{{sfn|Balanis|1989}}  Optical fiber began to receive special attention in the 1960s due to its importance to the communications industry.

The development of radio communication initially occurred at the lower frequencies because these could be more easily propagated over large distances.  The long wavelengths made these frequencies unsuitable for use in hollow metal waveguides because of the impractically large diameter tubes required.  Consequently, research into hollow metal waveguides stalled and the work of Lord Rayleigh was forgotten for a time and had to be rediscovered by others.  Practical investigations resumed in the 1930s by [[George C. Southworth]] at [[Bell Labs]] and [[Wilmer L. Barrow]] at [[MIT]].  Southworth at first took the theory from papers on waves in dielectric rods because the work of Lord Rayleigh was unknown to him.  This misled him somewhat; some of his experiments failed because he was not aware of the phenomenon of [[waveguide cutoff frequency]] already found in Lord Rayleigh's work.  Serious theoretical work was taken up by [[John R. Carson]] and [[Sallie Pero Mead|Sallie P. Mead]].  This work led to the discovery that for the TE<sub>01</sub> mode in circular waveguide losses go down with frequency and at one time this was a serious contender for the format for long-distance telecommunications.{{sfn|Oliner|2006|loc=[https://www.worldradiohistory.com/BOOKSHELF-ARH/History/History-Of-Wireless.pdf Reprint]}}{{rp|544–548}}

The importance of [[radar]] in [[World War II]] gave a great impetus to waveguide research, at least on the [[Allies of World War II|Allied]] side.  The [[magnetron]], developed in 1940 by [[John Randall (physicist)|John Randall]] and [[Harry Boot]] at the University of Birmingham in the United Kingdom, provided a good power source and made microwave radar feasible.  The most important centre of US research was at the [[Radiation Laboratory (MIT)|Radiation Laboratory]] (Rad Lab) at [[MIT]] but many others took part in the US, and in the UK such as the [[Telecommunications Research Establishment]].  The head of the Fundamental Development Group at Rad Lab was [[Edward Mills Purcell]].  His researchers included [[Julian Schwinger]], [[Nathan Marcuvitz]], Carol Gray Montgomery, and [[Robert H. Dicke]].  Much of the Rad Lab work concentrated on finding [[lumped element model]]s of waveguide structures so that components in waveguide could be analysed with standard circuit theory.  [[Hans Bethe]] was also briefly at Rad Lab, but while there he produced his small aperture theory which proved important for [[waveguide filter#Resonant cavity filter|waveguide cavity filters]], first developed at Rad Lab.  The German side, on the other hand, largely ignored the potential of waveguides in radar until very late in the war.  So much so that when radar parts from a downed British plane were sent to [[Siemens & Halske]] for analysis, even though they were recognised as microwave components, their purpose could not be identified.
{{blockquote|At that time, microwave techniques were badly neglected in Germany.  It was generally believed that it was of no use for electronic warfare, and those who wanted to do research work in this field were not allowed to do so.|H. Mayer, wartime vice-president of Siemens & Halske}}
German academics were even allowed to continue publicly publishing their research in this field because it was not felt to be important.{{sfn|Oliner|2006}}{{rp|548–554}}{{sfn|Levy|Cohn|1984}}{{rp|1055,1057}}

Immediately after World War II waveguide was the technology of choice in the microwave field.  However, it has some problems; it is bulky, expensive to produce, and the cutoff frequency effect makes it difficult to produce wideband devices.  Ridged waveguide can increase bandwidth beyond an octave, but a better solution is to use a technology working in [[Transverse mode|TEM mode]] (that is, non-waveguide) such as [[coaxial]] conductors since TEM does not have a cutoff frequency.  A shielded rectangular conductor can also be used and this has certain manufacturing advantages over coax and can be seen as the forerunner of the planar technologies ([[stripline]] and [[microstrip]]).  However, planar technologies really started to take off when printed circuits were introduced.  These methods are significantly cheaper than waveguide and have largely taken its place in most bands.  However, waveguide is still favoured in the higher microwave bands from around [[Ku band]] upwards.{{sfn|Oliner|2006}}{{rp|556–557}}{{sfn|Han|Hwang|2012}}{{rp|21-27,21-50}}