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== History ==
{{see also|Distributed element filter#History|Waveguide filter#History|Planar transmission line#History}}
[[File:Heaviside face.jpg|thumb|upright|alt=Photo of a bearded, middle-aged Oliver Heaviside|Oliver Heaviside]]
Distributed element modelling was first used in electrical network analysis by [[Oliver Heaviside]]<ref>Heaviside (1925).</ref> in 1881. Heaviside used thisit to find a correct description ofdescribe the behaviour of signals on the [[transatlantic telegraph cable]]. Transmission of early transatlantic telegraph had been difficult and slow due to an effect now called [[dispersion (optics)|dispersion]], butan effect thiswhich was not well understood at the time. Heaviside's analysis, now referred toknown as the [[telegrapher's equations]], identified the problem and suggested<ref>Heaviside (1887).</ref> [[loading coil|methods for overcoming it]]. It This is stillremains the standard analysis of transmission lines.<ref>Brittain, p. 39.</ref>
[[Warren P. Mason]] was the first to investigate the possibility of distributed element circuits., Heand filed a patent<ref>Mason (1930).</ref> in 1927 for a coaxial filter designed by this method. Mason and Sykes published the definitive paper on the method in 1937. Mason was also the first to suggest a distributed element acoustic filter in his 1927 doctoral thesis, and a distributed element mechanical filter in a patent<ref>Mason (1961).</ref> filed in 1941. In fact, theThe acoustic work had come first, and as a result of it Mason's colleagues atin the [[Bell Labs]] in the Radioradio Departmentdepartment requestedasked him to assist with coaxial and waveguide filters.<ref>{{multiref|Johnson ''et al.'' (1971), p. 155.|Fagen & Millman, p. 108.|Polkinghorn (1973).}}.</ref>
Mason's work was concerned with the coaxial form and other conducting wires, although much of it could also be adapted for waveguide. Prior toBefore [[World War II]], there was not muchlittle calldemand for distributed element circuits.; Thethe frequencies chosenused for radio transmissions at the time were always lower than the point at which distributed elements became advantageous. This was due to lowerLower frequencies havinghad a greater range, a primary consideration for [[Broadcasting|broadcast]] purposes.; This all changed withhowever, the wartime requirements for radar. changed that. There was a surge in distributed element filter development (an essential component of radars), and the technology was extended from the coaxial ___domain into the waveguide ___domain.<ref>Levy & Cohn, p. 1055.</ref>
The wartime work was mostly not publishedunpublished until after the war for secrecysecurity reasons., Thiswhich made it difficult to disentangleascertain who exactly was responsible for each development. An important centre for this research was the [[MIT Radiation Laboratory]] (Rad Lab), but work was also undertakendone elsewhere in the US and Britain. The Rad Lab work was published<ref>Fano & Lawson (1948).</ref> by Fano and Lawson.<ref>Levy & Cohn, p. 1055.</ref> Another wartime development was the hybrid ring. This work was carried out at [[Bell Labs]], and was published<ref>Tyrrell (1947).</ref> after the war by W. A. Tyrrell. Tyrrell describes hybrid rings implementedused in waveguide, and analyses them in terms of the well -known waveguide [[magic tee]]. However, otherOther researchers<ref>{{multiref|Sheingold & Morita (1953).|Albanese & Peyser (1958).}}.</ref> soon published coaxial versions of this device.<ref>Ahn, p. 3.</ref>
George Matthaei led a research group at [[Stanford Research Institute]] thatwhich included [[Leo C. Young|Leo Young]]. The groupand was responsible for many filter designs. Matthaei himself first described the interdigital filter<ref>Matthaei (1962).</ref> and the combline filter.<ref>Matthaei (1963).</ref> The group's work was published<ref>Matthaei ''et al.'' (1964).</ref> in a landmark 1964 book in 1964 covering the state of distributed element circuit design at that time. , Itwhich remained a major reference work for many years.<ref>Levy and Cohn, pp. 1057–1059..</ref>
Planar formats startedbegan to takebe offused with the invention of [[stripline]] by [[Robert M. Barrett]]. Although Striplinestripline was another wartime invention, but theits details were not published<ref>Barrett & Barnes (1951).</ref> until 1951. [[Microstrip]], invented in 1952,<ref>Grieg and Englemann (1952).</ref> became a commercial rival toof stripline. ; Howeverhowever, planar formats did not start to become widely used in microwave applications until better dielectric materials became available for the substrates in the 1960s.<ref>Bhat & Koul, p. 3.</ref> Another structure thatwhich had to wait for better materials was the dielectric resonator. Its advantages of (compact size and high quality) were first pointed out<ref>Richtmeyer (1939).</ref> by R. D. Richtmeyer in 1939. However, but materials with good temperature stability were not founddeveloped until the 1970s. Dielectric resonator filters are now common in both waveguide and transmission line filters.<ref>Makimoto & Yamashita, pp. 1–2.</ref>
OnTheoretical thedevelopments theoreticalincluded front,[[Paul anI. important development was theRichards]]' [[commensurate line theory]], ofwhich [[Paul I. Richards]]was published<ref>Richards (1948).</ref> in 1948. [[Kuroda's identities]], an important set of transforms{{Technical thatstatement|date=December 2018}} which allowed many designs to be practically implemented, were providedpublished<ref>{{multiref|First English publication:|Ozaki & Ishii (1958).}}.</ref> by Kuroda in 1955.<ref>Levy & Cohn, pp. 1056–1057.</ref>
== References ==
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