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=== Taper ===
A taper is a transmission line with a gradual change in cross-section. It can be considered the limiting case of the stepped impedance structure with an infinite number of steps.<ref>Zhurbenko, p. 310</ref> Tapers are a simple way of joining two transmission lines of different characteristic impedances. Using tapers greatly reduces the mismatch effects that a direct join would cause. If the change in cross-section is not too great, no other matching circuitry may be needed.<ref>Garg ''et al.'', pp. 180–181</ref> Tapers can provide [[Planar transmission line#Transitions|transitions]] between lines in different media, especially different forms of planar media.<ref>{{multiref|Garg ''et al.'', pp. 404–406, 540|Edwards & Steer, p. 493}}</ref> Tapers commonly change shape linearly<ref>Sangam and Kshetrimayum</ref>, but a variety of other profiles may be used. The profile that achieves a specified match in the shortest length is known as a Klopfenstein taper and is based on the [[Chebychev filter]] design.<ref>{{multiref|Zhurbenko, p. 311|Misra, p. 276|Lee, p. 100}}</ref>
Tapers can be used to match a transmission line to an antenna. In some designs, such as the [[horn antenna]] and [[Vivaldi antenna]], the taper is itself the antenna. Horn antennae, like other tapers, are often linear, but the best match is obtained with an exponential curve. The Vivaldi antenna is a flat (slot) version of the exponential taper.<ref>{{multiref|Bakshi & Bakshi|pp. 3-68–3-70|Milligan, p. 513}}</ref>
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