Chapter - 3 Transmission Lines Flashcards
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
Transmission Lines
Two Main Categories of Transmission Lines
- Guided
- Unguided
those with some form of conductor that provides a conduit which electromagnetic energy are contained
Guided Media (wired)
signals are emitted then radiated through air or vacuum those signals propagating down the unguided transmission media are available to anyone who has a device capable of receiving them
Unguided (Wireless)
Types of Transmission Lines
- Balanced
- Unbalanced
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 direction
Balanced Transmission Lines
it has an advantage that most noise interference is induce equally in both wires, producing longitudinal currents that cancel in the load
Balanced Transmission Lines
Example of Balanced Transmission Lines are
Parallel Conductor Transmission Lines
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. its disadvantages is its reduced immunity to common mode signals
Unbalanced Transmission Lines
Example of Unbalanced Transmission Lines are
Coaxial Cable Transmission Lines
current flows in opposite directions are known as
metallic circuit currents
current flows in same directions are known as
longitudinal circuit currents
balun stands for
balanced and unbalanced
- use to connect balanced and unbalanced transmission lines
most common type of balun is
Narrowband Balun which is also known as choke , sleeve or bazooka
balun has turns ratio of
4 : 1
it is comprised of two or more metallic conductors , separarted by non conductive insulating material known as dielectric (air , rubber , polyethylene , paper ,mica , glass and teflon ).
Parallel Conductor Transmission Lines
it is also known as ladder cable , which consist 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 distance between conductors is generally between 2 to 6 inches. but because no shielding radiation losses are high
Open Wire Line
primary use : voice-grade telephone
it is also known as ribbon cable. and it is the same with open wire transmission lines 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 between two conductors is 5/16 inches for Television Transmission Cable. the most common dielectric is TEFLON (polytetrafluoroethylene)
Twin Lead
primary use : television to rooftop antenna
it is formed by twisting together two insulated conductors around each other; the purpose of twisting is to reduce the effects of EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference)
Twisted Pair : UTP and STP
primary use : Local Area Network because it is easy to install and inexpensive
it consist of two copper wires where each wire is separately encapsulated in PVC ( polyvinyl chloride ) insulation
it is inexpensive , flexible and easy to install but it is also the most susceptible to external electromagnetic interference
UTP - Unshielded Twisted Pairs
the minimum number of twist for UTP is
Two Twist per Foot
7 types of UTP according to EIA/TIA 568 Standard:
Level 1 , 2 , Category 3 ,4 ,5 Enhanced Category 5 and Category 6
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 FOIL
if sleeve is woven into a mesh it is known as BRAID
more expensive than UTP but greater security and greater immunity to interference
STP - Shielded Twisted Pair
7 typer of STP according to EIA/TIA 568 Standard:
Category 3,4,5 Enhanced Category 5 , Category 7 , Foil Twisted Pair , and Shielded Foil Twisted Pair.
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.
Crosstalk
for twisted pair as category number increases
the number of twist also increases and also the information capacity
UTP Connectors are:
RJ:(registerred jack)
- 45
- 11
it consist of center conductor surrounded by a dielectric material, then a concentric shielding, and finally a rubber environmental protection outer jacket
it provide excellent shielding against external interference, it is commonly used in high frequency applications to reduce losses and to isolate transmission paths
Coaxial Cable
types of coaxial cable:
- Rigid Air-Filled Coaxial Cable
- Solid Flexible 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.
Rigid Air-Filled 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 color).
Solid Flexible Coaxial Cable
are military standards and specifications for coaxial cables by the US Department of Defense
RG ( Radio Government )
Coaxial Cable Connectors:
- BNC ( Bayonet Neil Concealman ) Connector
- N-Type Connector
it is also known as bayonet mount as they can easily twisted on or off
BNC
it is threaded and must be screwed on and off
N-Type Connector
refers to the woven stranded mesh that surrounds some types of coaxial cables
Shielding
coax with one layer of foil and one layer of braided shielding is known
Dual Shielding
there is also Quad Shielding which is two foil and two braided shielding
the characteristics of a transmission lines are determined by its ______, such as wire conductivity and insulator dielectric constant, and its ______, such as wire diameter and conductor spacing
electrical properties and physical properties
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 )
Primary Constants
RL // RC - lumped parameters
primary constants:
–series resistance and series inductance
ohm/length and henry/length
–shunt conductance and shunt capacitance
siemen / length and farad / length
parallel conductor transmission line
Series Inductance :
L=(u/pi) ln(2S/d)
where :
S= Separation or Distance between two Conductors
parallel conductor transmission line
Series Capacitance :
C=(pi x e/ ln(2S/d)
where:
e=permittivity of medium
d=diameter of inner diameter
Coaxial Cable Transmission Line
Series Inductance :
L= (u/2pi) ln (D/d)
where:
D=inside diameter of the outer conductor
parallel conductor transmission line
Series Capacitance :
C=2 pi e / ln (D/d)
where:
e=permittivity of medium
d=diameter of inner diameter
these are the transmission characteristics of a transmission lines:
Secondary Constant:
- Characteristic Impedance
- Propagation Constant
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
Characteristic Impedance Formula:
Zo = sqrt ( R + JwL / G + JwC )