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436:. The bottom of this board is left completely covered in copper and forms the bottom ground plane. A second board is clamped on top of the first. This second board has no pattern on the bottom and plain copper on the top to form the top ground plane. A sheet of copper foil may be wrapped around the two boards to electrically bond the two ground planes firmly together. On the other hand, stripline for high power applications such as radar will more likely be made as solid metal strips with periodic dielectric supports, essentially air dielectric.
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Underground telegraph cables into large buildings or between stations often needed to carry multiple independent telegraph lines. These cables took the form of multiple insulated conductors enclosed by a metal screen and overall protective jacket. In such cables the screen can be used as the return
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is similar to stripline but is open above the conductor. There is no dielectric or ground plane above the transmission line, there is only dielectric and a ground plane below the line. Microstrip is a popular format, especially in domestic products, because microstrip components can be made using
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circuits with microstrip components. Furthermore, since the board has to be made anyway, the microstrip components have no additional manufacturing cost. For applications where performance is more important than cost a ceramic substrate might be used instead of a printed circuit. Microstrip has
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and highly predictable transmission parameters. The latter is a result of the fixed geometry of the format which leads to a precision not found with loose wires. Open wire systems are also affected by nearby objects altering the field pattern around the conductor. Coax does not suffer from this
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coding. In these systems the cost of the return conductor was not so significant (one conductor in seven for
Schilling's earliest needle telegraph and one conductor in six for the Cooke and Wheatstone telegraph) but the number of coding conductors was progressively reduced with improved systems.
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Planar transmission lines are used for far more than merely connecting components or units together. They can themselves be used as components and units. Any transmission line format can be used in this way, but for the planar formats it is often their primary purpose. Typical circuit blocks
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for the return path. This compares well with balanced cabling which requires two conductors for each line, nearly twice as many. Another benefit of unbalanced lines is that they do not require more expensive, balanced driver and receiver circuits to operate correctly.
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lines (telephone invented 1876) used the same transmission line scheme as telegraph of unbalanced single wires. However, telephone communication started to suffer after the widespread introduction of electrical power lines. Telephone transmission started to use
489:. At microwave frequencies discrete components need to be impractically small and a transmission line solution is the only viable one. On the other hand, at low frequencies such as audio applications, transmission line devices need to be impractically large.
348:(triax) is a variant of coax with a second shield conductor surrounding the first with a layer of insulation in between. As well as providing additional shielding, the outer conductors can be used for other purposes such as providing power to equipment or
179:, but these are entirely separate concepts. The former is a cabling scheme while the latter is a signalling scheme. However, single-ended signalling is commonly sent over unbalanced lines. Unbalanced lines are not to be confused with
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Any line that has a different impedance of the return path may be considered an unbalanced line. However, unbalanced lines usually consist of a conductor that is considered the signal line and another conductor that is
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The chief advantage of the unbalanced line format is cost efficiency. Multiple unbalanced lines can be provided in the same cable with one conductor per line plus a single common return conductor, typically the
270:(1843). In such systems the cost of a return conductor was fully 50 per cent of the cable costs. It was discovered that a return conductor could be replaced with a return path through the Earth using
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Connections within integrated circuits are normally planar so planar transmission lines are a natural choice where these are needed. The need for transmission lines is most frequently found in
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communications. These consisted of single wires strung between poles. The return path for the current was originally provided by a separate conductor. Some early telegraph systems, such as
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Electric power distribution is normally in the form of balanced three-phase transmission. However, in some remote locations where a relatively small amount of power is required, a
326:. It was originally constructed from rigid copper pipes, but the usual form today is a flexible cable with a braided screen. The advantages of coax are a theoretically perfect
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is a flat conductor with a ground plane both above and below the conductor. The variant of stripline where the space between the two ground planes is completely filled with a
318:(coax) has a central signal conductor surrounded by a cylindrical shielding conductor. The shield conductor is normally grounded. The coaxial format was developed during
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and thus manufacturing tolerances and minimum width are less critical on high-impedance lines. A drawback of microstrip is that the mode of transmission is not entirely
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Planar format transmission lines are flat conductors manufactured by a number of techniques on to a substrate. They are nearly always an unbalanced format. At the low
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used by telephones are relatively low and transmission line theory only becomes significant for distances of at least between buildings. However, at the higher
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which use two identical conductors to maintain impedance balance throughout the line. Balanced and unbalanced lines can be interfaced using a device called a
204:. The ground conductor may be, and often is, common to multiple independent circuits. For this reason the ground conductor may be referred to as
461:. Strictly speaking, standard transmission line analysis does not apply because other modes are present, but it can be a usable approximation.
473:(MICs). There are a great many materials and techniques used to make MICs, and transmission lines can be formed in any of these technologies.
413:. Planar technologies were developed for these kinds of small size applications and are not very appropriate for long distance transmissions.
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Coaxial lines are the norm for connections between radio transmitters and their antennae, for interconnection of electronic equipment where
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This article is about the electrical transmission line. For the
American football offensive line, see
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system invented for the telegraph, but rarely used today. Unbalanced lines are to be contrasted with
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the established manufacturing techniques of printed circuit boards. Designers are thus able to mix
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282:, effectively a coaxial cable. The first transatlantic cable of this kind was completed in 1866.
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another small advantage over stripline; the line widths are wider in microstrip for the same
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a device, just a matter of centimetres. At the very high data rates handled by modern
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spikes. Using earth return was a significant cost saving and rapidly became the norm.
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since the field is entirely contained within the cable due to the surrounding screen.
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to combat this problem and the modern norm for telephone presentation is the balanced
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conductor. Undersea telegraph cables were usually a single conductor protected by
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432:. Stripline can be manufactured by etching the transmission line pattern on to a
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is a pair of conductors intended to carry electrical signals, which have unequal
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for a circuit design when the transmission was over many miles. Similarly, the
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used by
British railways required multiple code wires. Essentially, they were
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20:. For three-phase electric power lines carrying unbalanced currents, see
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outside the historic Alice
Springs telegraph station on the now disused
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Soon only one coding wire was required with the data being transmitted
196:, or is ground itself. The ground conductor often takes the form of a
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Microstrip parallel-coupled transmission lines. The design forms a
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frequencies transmission line considerations can become important
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or above is involved, and were formerly widely used for forming
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262:. Important examples of these single-wire systems were the
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The earliest use of unbalanced transmission lines was for
352:. Triax is widely used for the connection of cameras in
568:"A Technology of Thin-Film Hybrid Microwave Circuits"
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of early telegraph it was only necessary to consider
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before twisted pair became popular for this purpose.
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and other circuits. Examples of unbalanced lines are
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Glossary of
American football § unbalanced line
572:IEEE Transactions on Parts, Hybrids, and Packaging
22:Three-phase electric power § Unbalanced loads
251:1837 Cooke & Wheatstone five-needle telegraph
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107:able to support 25 unbalanced transmission lines
56:but its sources remain unclear because it lacks
268:Cooke & Wheatstone single-needle telegraph
175:Unbalanced lines are sometimes confused with
505:on a single-wire earth return line in Canada
553:The Worldwide History of Telecommunications
477:implemented by transmission lines include
87:Learn how and when to remove this message
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483:directions couplers and power splitters
183:which do not use a return path at all.
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566:Curran, J.E.; Jeanes, R.; Sewell, H,
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232:Australian Overland Telegraph Line
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574:, vol. 12, iss. 4, December 1976.
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555:, John Wiley & Sons, 2003
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428:material is sometimes known as
181:single-wire transmission lines
167:circuits can all use the same
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471:microwave integrated circuits
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127:along their lengths and to
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511:single-wire earth return
387:transmission line theory
366:Planar transmission line
42:This article includes a
177:single-ended signalling
71:more precise citations.
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503:pole-mount transformer
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226:Telegraph lines on an
218:Earth-return telegraph
163:. Likewise, multiple
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551:Huurdeman, Anton A.,
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434:printed circuit board
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513:system may be used.
328:electrostatic screen
588:Electrical circuits
465:Integrated circuits
407:computer processors
383:transmission speeds
360:Planar technologies
340:local area networks
187:General description
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493:Power transmission
487:impedance matching
450:discrete component
411:integrated circuit
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354:television studios
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245:1832 experimental
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113:telecommunications
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44:list of references
395:radio frequencies
391:audio frequencies
280:steel-wire armour
202:screen of a cable
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538:Huurdeman, p. 67
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376:band-pass filter
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228:Oppenheimer pole
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63:Please help
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322:for use in
243:Schilling's
69:introducing
561:0471205052
517:References
459:transverse
445:Microstrip
440:Microstrip
426:dielectric
165:microstrip
143:, such as
125:impedances
455:impedance
422:Stripline
417:Stripline
399:microwave
287:telephone
272:grounding
145:twin-lead
77:June 2023
582:Category
430:triplate
260:serially
249:and the
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479:filters
298:cable.
200:or the
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403:inside
285:Early
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153:balun
50:, or
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397:and
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