A report on Coaxial cable and Transmission line

In his 1880 British patent, Oliver Heaviside showed how coaxial cable could eliminate signal interference between parallel cables.
Schematic of a wave moving rightward down a lossless two-wire transmission line. Black dots represent electrons, and the arrows show the electric field.
Coaxial cable cutaway (not to scale)
One of the most common types of transmission line, coaxial cable.
Schematic representation of the elementary components of a transmission line
Variations on the schematic electronic symbol for a transmission line.
Schematic representation of a coaxial transmission line, showing the characteristic impedance Z_0
RG-6 coaxial cable
A transmission line is drawn as two black wires. At a distance x into the line, there is current I(x) travelling through each wire, and there is a voltage difference V(x) between the wires. If the current and voltage come from a single wave (with no reflection), then V(x) / I(x) = Z0, where Z0 is the characteristic impedance of the line.
RG-142 coaxial cable
Standing waves on a transmission line with an open-circuit load (top), and a short-circuit load (bottom). Black dots represent electrons, and the arrows show the electric field.
RG-405 semi-rigid coaxial cable
A type of transmission line called a cage line, used for high power, low frequency applications. It functions similarly to a large coaxial cable. This example is the antenna feed line for a longwave radio transmitter in Poland, which operates at a frequency of 225 kHz and a power of 1200 kW.
High-end coaxial audio cable (S/PDIF)
A simple example of stepped transmission line consisting of three segments.
1+5/8 in flexible line
1-5/8" Heliax coaxial cable
Semi-rigid coax assembly
Semi-rigid coax installed in an Agilent N9344C 20GHz spectrum analyser
Early coaxial antenna feedline of 50 kW radio station WNBC, New York, 1930s
AT&T coaxial cable trunkline installed between East Coast and Midwest in 1948. Each of the 8 coaxial subcables could carry 480 telephone calls or one television channel.

Coaxial cable is a type of transmission line, used to carry high-frequency electrical signals with low losses.

- Coaxial cable

Types of transmission line include parallel line (ladder line, twisted pair), coaxial cable, and planar transmission lines such as stripline and microstrip.

- Transmission line
In his 1880 British patent, Oliver Heaviside showed how coaxial cable could eliminate signal interference between parallel cables.

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Coaxial cable feedline emerging from a VHF ground plane antenna.

Feed line

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Coaxial cable feedline emerging from a VHF ground plane antenna.
Complicated waveguide feed of a military radar

In a radio antenna, the feed line (feedline), or feeder, is the cable or other transmission line that connects the antenna with the radio transmitter or receiver.

The most widely used types of feed line are coaxial cable, twin-lead, ladder line, and at microwave frequencies, waveguide.

A stack of "fishbone" and Yagi–Uda television antennas

Antenna (radio)

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Antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver.

Antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver.

A stack of "fishbone" and Yagi–Uda television antennas
Animation of a half-wave dipole antenna radiating radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods connected to a radio transmitter (not shown). The transmitter applies an alternating electric current to the rods, which charges them alternately positive (+) and negative (−). Loops of electric field leave the antenna and travel away at the speed of light; these are the radio waves. In this animation the action is shown slowed down enormously.
Electronic symbol for an antenna
Antennas of the Atacama Large Millimeter/submillimeter Array.
An automobile's whip antenna, a common example of an omnidirectional antenna.
Half-wave dipole antenna
Diagram of the electric fields ( blue ) and magnetic fields ( red ) radiated by a dipole antenna ( black rods) during transmission.
Cell phone base station antennas
Standing waves on a half wave dipole driven at its resonant frequency. The waves are shown graphically by bars of color ( red for voltage, V and blue for current, I ) whose width is proportional to the amplitude of the quantity at that point on the antenna.
Typical center-loaded mobile CB antenna with loading coil
Polar plots of the horizontal cross sections of a (virtual) Yagi-Uda-antenna. Outline connects points with 3 dB field power compared to an ISO emitter.
The wave reflected by earth can be considered as emitted by the image antenna.
The currents in an antenna appear as an image in opposite phase when reflected at grazing angles. This causes a phase reversal for waves emitted by a horizontally polarized antenna (center) but not for a vertically polarized antenna (left).
frame

An antenna lead-in is the transmission line, or feed line, which connects the antenna to a transmitter or receiver.

Such a structure is normally connected to the return connection of an unbalanced transmission line such as the shield of a coaxial cable.

Schematic representation of the elementary components of a transmission line.

Telegrapher's equations

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Schematic representation of the elementary components of a transmission line.
Schematic showing a wave flowing rightward down a lossless transmission line. Black dots represent electrons, and the arrows show the electric field.
In the presence of losses the solution of the telegrapher's equation has both damping and dispersion, as visible when compared with the solution of a lossless wave equation.
Changes of the signal level distribution along the single dimensional transmission medium. Depending on the parameters of the telegraph equation, this equation can reproduce all four patterns.

The telegrapher's equations (or just telegraph equations) are a pair of coupled, linear partial differential equations that describe the voltage and current on an electrical transmission line with distance and time.

In long distance rigid coaxial cable, to get very low dielectric losses, the solid dielectric may be replaced by air with plastic spacers at intervals to keep the center conductor on axis.

Heaviside c. 1900

Oliver Heaviside

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English self-taught mathematician and physicist who brought complex numbers to circuit analysis, invented a new technique for solving differential equations (equivalent to the Laplace transform), independently developed vector calculus, and rewrote Maxwell's equations in the form commonly used today.

English self-taught mathematician and physicist who brought complex numbers to circuit analysis, invented a new technique for solving differential equations (equivalent to the Laplace transform), independently developed vector calculus, and rewrote Maxwell's equations in the form commonly used today.

Heaviside c. 1900
Comparison of before and after the restoration project.

Undertaking research from home, he helped develop transmission line theory (also known as the "telegrapher's equations").

That same year he patented, in England, the coaxial cable.

300 ohm twin-lead

Twin-lead

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Two-conductor flat cable used as a balanced transmission line to carry radio frequency signals.

Two-conductor flat cable used as a balanced transmission line to carry radio frequency signals.

300 ohm twin-lead
A 300-to-75-ohm balun, showing twin-lead on the right hand side

It can have significantly lower signal loss than miniature flexible coaxial cable, the main alternative type of feedline at these frequencies; for example, type RG-58 coaxial cable loses 6.6 dB per 100 m at 30 MHz, while 300 ohm twin-lead loses only 0.55 dB.

Twin-lead is also used in amateur radio stations as a transmission line for balanced transmission of radio frequency signals.

A transmission line drawn as two black wires. At a distance x into the line, there is current phasor I(x) traveling through each wire, and there is a voltage difference phasor V(x) between the wires (bottom voltage minus top voltage). If.

Characteristic impedance

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A transmission line drawn as two black wires. At a distance x into the line, there is current phasor I(x) traveling through each wire, and there is a voltage difference phasor V(x) between the wires (bottom voltage minus top voltage). If.
Consider one section of the transmission line for the derivation of the characteristic impedance. The voltage on the left would be V and on the right side would be This figure is to be used for both the derivation methods.

The characteristic impedance or surge impedance (usually written Z0) of a uniform transmission line is the ratio of the amplitudes of voltage and current of a single wave propagating along the line; that is, a wave travelling in one direction in the absence of reflections in the other direction.

The characteristic impedance of coaxial cables (coax) is commonly chosen to be 50 Ω for RF and microwave applications.

Radio frequency

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Oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around 20 kHz to around 300 GHz.

Oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around 20 kHz to around 300 GHz.

When conducted by an ordinary electric cable, RF current has a tendency to reflect from discontinuities in the cable, such as connectors, and travel back down the cable toward the source, causing a condition called standing waves. RF current may be carried efficiently over transmission lines such as coaxial cables.