CH:3 TRANSMISSION LINES

Transmission Line

It is a metallic conductor system used to transfer electrical energy from one point to another using electrical current flow, and it is designed to deliver RF power from the transmitter to the antenna and maximum signal from the antenna to the receiver.

Guided Transmission Media

Those with some form of conductor that provides a conduit in which electromagnetic energy are contained.

Unguided Transmission Media

Signals are emitted then radiated through air or a vacuum (those signals propagating down the unguided transmission media are available to anyone who has a device capable of receiving them).

BALANCED TRANSMISSION LINE, UNBALANCED TRANSMISSION LINE

TYPES OF TRANSMISSION LINES

BALANCED TRANSMISSION LINE

It is also known as differential transmission line, which is made up of two parallel conductors spaced from one another by a distance of 1/2 inch up to several inches, and both conductors carry signal currents, which are equal in magnitude with respect to electrical ground but travel in opposite directions (one conductor carries the signal and the other conductor is the return path).

BALANCED TRANSMISSION LINE

• It has an advantage that most noise interference is induced equally in both wires, producing longitudinal currents that cancel in the load.

• Examples of balanced transmission lines are parallel conductor transmission lines.

UNBALANCED TRANSMISSION LINE

It is also known as single-ended transmission lines or concentric transmission lines, which consists of a solid conductor surrounded by an insulator, wherein one wire is at ground potential and the other wire is at signal potential.

UNBALANCED TRANSMISSION LINE

It has the advantage of requiring only one wire for each signal, and only one ground line is required no matter how many signals are grouped into one conductor.

UNBALANCED TRANSMISSION LINE

• Its primary disadvantage is its reduced immunity to common-mode signals, such as noise and other interference.

• Examples of unbalanced transmission lines are coaxial cable transmission lines.

Metallic circuit currents

Currents that flow in opposite direction are known as

longitudinal circuit currents.

Currents that flow in the same direction are known as

Balun

This stands for balance to unbalanced. It is a circuit device used to connect a balanced transmission line to an unbalanced load.

Narrowband balun

The most common type of Balun; it is also known as a choke, sleeve, or bazooka balun. A certain balun has a typical turns ratio of 4:1

Parallel Conductor Transmission Line

• It is comprised of two or more metallic conductors (usually copper) separated by a non-conductive insulating material known as a dielectric (common dielectric materials include air, rubber, polyethylene, paper, mica, glass, and Teflon).

Open - Wire Line

It is also known as ladder cable, which consists of two parallel wires, closely spaced and separated by air; it has non-conductive spacers which are placed at periodic intervals for support and to keep the distance between the conductors constant (the distance between the two conductors is generally between 2 and 6 inches).

Open - Wire Line

Its advantage is its simple construction, however, because there is no shielding, radiation losses are high, and the cable is susceptible to picking up signals through mutual induction, which produces crosstalk.

Open - Wire Line

It is primarily used in standard voice-grade telephone applications.

Twin Lead

It is also known as ribbon cable, and it is the same with open wire transmission line except that the spacers between the two conductors are replaced with a continuous solid dielectric that ensures uniform spacing along the entire cable (the distance of two conductors is 5/16 inches for television transmission cable).

Twin Lead

• It uses commonly a dielectric material known as Teflon (polytetrafluoroethylene).

• It typically has a characteristic impedance of 300 ohms and is commonly used to connect televisions to rooftop antennas.

Twisted Pair

• It is formed by twisting together two insulated conductors around each other, the purpose of twisting is to reduce the effects of EMI (electromagnetic field interference) and RFI (radio frequency interference) from external sources.

Twisted Pair

• It is used for most local area networks because it is easy to install and inexpensive when compared to coaxial and optical fiber cables.

UTP (Unshielded twisted pair) and STP (shielded twisted pair)

Twisted Pair has two types

UTP (Unshielded Twisted Pair)

• It consists of two copper wires where each wire is separately encapsulated in PVC (polyvinyl chloride) insulation.

• It is inexpensive, flexible, and easy to install (it is the least expensive transmission medium), but it is also the most susceptible to external electromagnetic interference.

• The minimum number of twists for UTP cables is two (2) twists per foot.

• There are seven primary UTP cables classified by the EIA/TIA 568 standard:

  • Level 1

  • Level 2

  • Category 3

  • Category 4

  • Category 5

  • Enhanced Category 5

  • Category 6

Shielded Twisted Pair (STP)

• It consists of two copper conductors separated by a solid dielectric material, and its wires and dielectric are enclosed in a conductive metal sleeve known as a foil (if the sleeve is woven into a mesh, it is known as a braid).

• It is thicker and less flexible than UTP cable, making it more difficult and expensive to install.

• It requires additional grounding connector and is more expensive to manufacture, but offers:

  • Greater security

  • Greater immunity to interference

• There are seven primary STP cables classified by the EIA/TIA 568 standard: Category 3, Category 4, Category 5, enhanced category 5, category 7, foil twisted pair, and shielded-foil twisted pair.

Category:
Level 1 (UTP)

Applications: Standard voice and low-speed data
Data Rate: 2400bps
Distance: 18000ft

Level 2 (UTP)

Applications: Standard voice and low-speed data
Data Rate: 4Mbps
Distance: 18000ft

Category 3 (UTP/STP)

Applications: Low-speed local area networks
Data Rate: 16 Mbps and all level 2 applications
Distance: 100 m

Category 4 (UTP/STP)

Applications: Low-speed local area networks
Data Rate: 20 Mbps and all CAT 3 Applications
Distance: 100 m

Category 5 (UTP/STP)

Applications: High-speed local area networks
Data Rate: 100 Mbps
Distance: 100 m

Enhanced Category 5 (UTP/STP)

Applications: High-speed local area networks and asynchronous transfer mode (ATM)
Data Rate: 350 Mbps
Distance: 100 m or more

Category 6 (UTP/STP)

Applications: Very high-speed local area networks and asynchronous transfer mode (ATM)
Data Rate: 550 Mbps
Distance: 100 m or more

Category 7 Shielded Screen Twisted Pair (SSTP)

Applications: Ultrahigh-speed local area networks and asynchronous transfer mode (ATM)
Data Rate: 1Gbps
Distance: 100 m or more

Foil Twisted Pair (STP)

Applications: Ultrahigh-speed local area networks and asynchronous transfer mode (ATM); designed to minimized EMI susceptibility and maximize EMI immunity
Data Rate: >1Gbps

Shielded Foil Twisted Pair (STP)

Applications: Ultrahigh-speed local area networks and asynchronous transfer mode (ATM); designed to minimized EMI susceptibility and maximize EMI immunity
Data Rate: >1Gbps

Crosstalk

Is an electromagnetic interference between two conductors that occurs when current flows through one conductor, it produces a magnetic field that can interfere with the adjacent conductor.

For Twisted Pair cables

As the category number increases, the number of twists increases and the information capacity also increases.

RJ Connectors

• are UTP connectors such as RJ-45 and RJ-11, RJ stands for Registered jack.

• RJ-45 has 8 connections

• RJ-11 has 6 connections

COAXIAL CABLE TRANSMISSION LINE

• It consists of a center conductor surrounded by a dielectric material, then a concentric shielding, and finally a rubber environmental protection outer jacket.

• It provides excellent shielding against external interference; it is commonly used in high-frequency applications to reduce losses and to isolate transmission paths.

Rigid Air-Filled Coaxial Cable, Solid Flexible Coaxial Cable

TYPES OF COAXIAL CABLE TRANSMISSION LINES

Rigid Air-Filled Coaxial Cable

It has a center conductor surrounded coaxially by a tubular outer conductor, and the insulating material is air (some are pressurized with an inert gas to prevent moisture from entering).

Solid Flexible Coaxial Cable

It consists of a flexible inner conductor and a concentric outer conductor of metal braid. The two are separated by a continuous insulating material (commonly Teflon, which is white in color).

CHARACTERISTIC IMPEDANCE OF COMMON COAXIAL CABLES:
Type Number: RG-8/U

IMPEDANCE (Ω):
50 Ω

CHARACTERISTIC IMPEDANCE OF COMMON COAXIAL CABLES:
Type Number: RG-8/A-AU

IMPEDANCE (Ω)
52 Ω

CHARACTERISTIC IMPEDANCE OF COMMON COAXIAL CABLES:
Type Number: RG-11

IMPEDANCE (Ω)
75 Ω

CHARACTERISTIC IMPEDANCE OF COMMON COAXIAL CABLES:
Type Number: RG-58

IMPEDANCE (Ω)
50 Ω

CHARACTERISTIC IMPEDANCE OF COMMON COAXIAL CABLES:
Type Number: RG-58/A-AU

IMPEDANCE (Ω)
53 Ω

CHARACTERISTIC IMPEDANCE OF COMMON COAXIAL CABLES:
Type Number: RG-59

IMPEDANCE (Ω)
75 Ω

CHARACTERISTIC IMPEDANCE OF COMMON COAXIAL CABLES:
Type Number: RG-59/A-AU

IMPEDANCE (Ω)
73 Ω

CHARACTERISTIC IMPEDANCE OF COMMON COAXIAL CABLES:
Type Number: RG-214

IMPEDANCE (Ω)
50 Ω

RG (radio government)

are military standards and specifications for coaxial cables by the US Department of Defense

BNC (Bayonet Neil Concealman) Connector

it is also known as bayonet mount as they can easily twisted on or off.

N-type Connector

it is threaded and must be screwed on and off.

Shielding

refers to the woven stranded mesh that surrounds some types of coaxial cables.

Dual shielded

A coaxial cable with one layer of foil insulation and one layer of braided shielding is known as?

Quad shielding

Environments that are subject to high interference used, which consists of two layers of foil insulation and two layers of braided metal shielding

Uniformly Distributed Transmission Line

The characteristics of a transmission line are determined by its electrical properties, such as wire conductivity and insulator dielectric constant, and its physical properties, such as wire diameter and conductor spacing.

Primary Constants

These are uniformly distributed throughout the length of the line and are commonly known as distributed parameters
(The combined parameters are known as lumped parameters).

Series Resistance (R)

It is the total resistance of the transmission line per unit length, including both line conductors (both combinations of conductors making up the two sides of the line).
📏 Unit: Ohm per unit length

Series Inductance (L)

It is the total series inductance of the transmission line per unit length, including inductance due to magnetic flux both internal and external to the conductors.
📏 Unit: Henry per unit length

Shunt Conductance (G)

It is the shunt conductance of the transmission line per unit length. It is the circuit representation of losses that are proportional to the square of the voltage between the conductors or the square of the electric field in the medium.
📏 Unit: Siemens per unit length

Shunt Capacitance (C)

it is the shunt capacitance of the transmission line per unit length. It is usually expressed in Farad per unit length.

Secondary Constants

These are the Transmission Characteristics of a transmission line. Examples are: Characteristic Impedance, Propagation Constant

Characteristic Impedance

It is also known as surge impedance, and it is defined as the impedance seen looking into an infinite long line or the impedance seen looking into a finite length of a line that is terminated in a purely resistive load with resistance equal to the characteristic impedance of the line.

Characteristic Impedance

It is a complex quantity that is expressed in Ohms, and is ideally independent of length, and cannot be directly measure.

Propagation Constant

It is also known as propagation coefficient that is used to express the attenuation (signal loss) and the phase shift per unit length of the transmission lines.

WAVE PROPAGATION IN A TRANSMISSION LINE:
Velocity Factor

It is also known as velocity constant, and it is defined as the ratio of the actual velocity of propagation of an electromagnetic wave through a given medium to its velocity of propagation in free space (vacuum)

Dielectric Constant

It is simply the relative permittivity of a material, and it depends on the type of insulating material used.

Velocity Factor & Dielectric Constant of Some Materials:
Vacuum

Velocity Factor: 1.0000
Dielectric Constant: 1.0000

Velocity Factor & Dielectric Constant of Some Materials:
Air

Velocity Factor: 0.9997
Dielectric Constant: 1.0006

Velocity Factor & Dielectric Constant of Some Materials:
Teflon Foam

Velocity Factor: 0.8200
Dielectric Constant: 1.4872

Velocity Factor & Dielectric Constant of Some Materials:
Teflon

Velocity Factor: 0.6901
Dielectric Constant: 2.1000

Velocity Factor & Dielectric Constant of Some Materials:
Polyethylene

Velocity Factor: 0.6637
Dielectric Constant: 2.2700

Velocity Factor & Dielectric Constant of Some Materials:
Paper (Parafinned)

Velocity Factor: 0.6325
Dielectric Constant: 2.5000

Velocity Factor & Dielectric Constant of Some Materials:
Polystyrene

Velocity Factor: 0.6325
Dielectric Constant: 2.5000

Velocity Factor & Dielectric Constant of Some Materials:
Polyvinyl Chloride

Velocity Factor: 0.5505
Dielectric Constant: 3.3000

Velocity Factor & Dielectric Constant of Some Materials:
Rubber

Velocity Factor: 0.5774
Dielectric Constant: 3.0000

Velocity Factor & Dielectric Constant of Some Materials:
Mica

Velocity Factor: 0.4472
Dielectric Constant: 5.0000

Velocity Factor & Dielectric Constant of Some Materials:
Glass

Velocity Factor: 0.3651
Dielectric Constant: 7.5000

slower

• The velocity of propagation of a radio signal is __________ in a transmission line than in free space.

• This difference is expressed as the velocity factor for different types of transmission lines.

Coaxial Cable

has a velocity factor of 0.6 to 0.7 and for open wire line or twin lead is in the 0.7 to 0.8 range.

the velocity factor must be considered.

In computing the length of a transmission line at a specific frequency

DELAY LINES

• These are transmission lines designed to intentionally introduce a time delay in the path of the electromagnetic wave.

• The amount of time delay is a function of the transmission line’s inductance and capacitance.

Length of Transmission Line

The length of a transmission line relative to the length of the wave propagating down it is an important consideration when analyzing transmission line behavior.

Conductor Loss, Dielectric Heating Loss, Radiation Loss, Coupling Loss, Corona

Transmission Line Losses

Conductor Loss

• It is also known as conductor heating loss or I² R loss, and it is directly proportional to the square of the length of the line and inversely proportional to the characteristic impedance.

• It is inherent and unavoidable power loss because of the finiite resistance of the transmission lines, and depends somewhat on frequency because of a phenomenon known as skin effect
  

Dielectric Heating Loss

• It is caused by a difference of potential between conductors in a metallic transmission line (i.e., it is caused by the heating of the dielectric material between conductors, taking power from the source).

• It increases for solid dielectric lines because of gradually worsening properties with increasing frequency.

Radiation Loss

• If the separation between the conductors in a transmission line is an appreciable fraction of wavelength, the electrostatic and electromagnetic field that surrounds the conductor causes the line to act as an antenna (radiation of signal occurs).

• It depends on dielectric material, conductor spacing, and length of the transmission line, and it can be reduced by properly shielding the cable.

Coupling Loss

• It occurs whenever a connection is made to or from a transmission line, or when two sections of transmission lines are connected together.

Corona

• It is a luminous discharge that occurs between the two conductors of a transmission line when the difference of potential between them exceeds the breakdown voltage of the dielectric insulator.

• When this occurs, usually the transmission line is destroyed.

Skin Effect

is a phenomenon wherein the signals tend to propagate at the outer edge of the cable if the frequency of operation is too high.
This happens when frequency increases, the region of high current density becomes thinner, reducing the cross-sectional area and increasing the resistance of the conductor.

NON-RESONANT TRANSMISSION LINE

• Also known as a flat line or a matched line, wherein there is no reflected power in the transmission line.

• A transmission line is non-resonant if it is of infinite length or if it is terminated with a resistive load equal to the ohmic value of the characteristic impedance of the transmission line.

  Z_O = Z_L

RESONANT TRANSMISSION LINE

• Also known as a mismatched line, in which the load impedance is not equal to the characteristic impedance of the line, so some of the incident power is reflected back to the load.

• In a resonant line, the energy is alternately transferred between the magnetic and electric fields of the distributed inductance and capacitance of the line.

  Z_O is not equal Z_L Z_L = R+jX

  Z_L = open Z_L = shorted

Reflection Coefficient

it is also known as coefficient of reflection, wherein it is a vector quantity that represent the ratio of the reflected voltage to the incident voltage or reflected current to the incident current.

Standing Wave Ratio

• It is defined as the ratio of the maximum voltage or current to the minimum voltage or current of a standing wave in a transmission line.

• It is a measure of mismatch between the load impedance and the characteristic impedance of a transmission line.

Typical Value

Reflection Coefficient: Γ<1
Standing Wave ratio: SWR > 1

Ideal Value

Reflection Coefficient: Γ=0
Standing Wave Ratio: SWR = 1

Worse - Case Value

Reflection Coefficient: Γ=±1
Standing Wave ratio: SWR = ∞

Standing Wave

• It is an interference pattern setup by two travelling waves.

• It is the formation of which due to the interaction between the incident and reflected waves that causes what appears to the stationary pattern of waves on the line.

Standing Wave on an Open-Circuited Line:

• The voltage incident wave is reflected back just as if it were to continue down the line.

• The current incident wave is reflected 180 degrees from how it would have continued.

• The sum of incident and reflected current waveforms is minimum at the open.

• The sum of incident and reflected voltage waveforms is maximum at the open.

Standing Wave on a Short-Circuited Line

• The voltage incident wave is reflected 180 degrees from how it would have continued.

• The current incident wave is reflected back just as if it were to continue down the line.

• The sum of incident and reflected current waveforms is maximum at the short.

• The sum of incident and reflected voltage waveforms is minimum at the short.