Air stripline
Structure
Structure
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[thumb\|upright\=1\.7\|Diagram of the structure of dielectric supported air stripline](/wiki/File:Air_stripline_structure.svg "Air stripline structure.svg")
Air stripline is a form of [stripline](/wiki/Stripline "Stripline") using air as the [dielectric](/wiki/Dielectric "Dielectric") material between the central conductor and the [ground planes](/wiki/Ground_plane "Ground plane"). Using air as the dielectric has the advantage that it avoids the [transmission losses](/wiki/Transmission_loss "Transmission loss") usually [associated with dielectric materials](/wiki/Dielectric_loss "Dielectric loss").Maichen, pp. 87–88

There are two basic ways that air stripline is constructed. In dielectric supported stripline, also called suspended stripline or suspended substrate, the strip conductor is deposited on a thin solid dielectric substrate, sometimes on both sides and connected together to form a single conductor.Oliner, p. 557–558 This substrate is then clamped in place between the walls supporting the two ground planes. In this method the strip can be manufactured by printed circuit techniques making it cheap and leading to the further advantage that other components can be printed on the dielectric in the same operation. The purpose of the solid dielectric is mechanical support for the conductor,Rosloniec, p. 253 but it is made as thin as possible to minimise its electrical effect. The flimsy nature of the substrate means that it can easily be distorted. Because of this, the design needs to take account of thermal stability issues.Han \& Hwang, p. 21\-60 High end designs may use a crystalline substrate, such as [boron nitride](/wiki/Boron_nitride "Boron nitride") or [sapphire](/wiki/Sapphire "Sapphire"), as the suspended substrate.Bhat \& Koul, p. 302

The other method of construction uses a more substantial solid metal bar as the strip, supported on periodically spaced insulators. This method may be more suitable for high power applications. In such applications the corners of the conductor cross\-section may be rounded to prevent high field intensities and [arcing](/wiki/Arcing "Arcing") occurring at those points. The insulators are electrically undesirable; they detract from the goal of having a purely air dielectric, add [discontinuities](/wiki/Discontinuity_%28transmission_lines%29 "Discontinuity (transmission lines)") to the line, and are potentially a point at which [tracking](/wiki/Electrical_treeing "Electrical treeing") can occur. In some components, there are points at which the lines need to be grounded, either directly or through a discrete component. In such circuits these grounding points can double as mechanical supports and the need for supporting insulators avoided.Matthaei *et al.*, pp. 422–423


Is air stripline more expensive than other types of stripline?