Chapter - 3 Transmission Lines

Question 1

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

Answer 1

Transmission Lines

Question 2

Two Main Categories of Transmission Lines

Answer 2

• Guided

- Unguided

Question 3

those with some form of conductor that provides a conduit which electromagnetic energy are contained

Answer 3

Guided Media (wired)

Question 4

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

Answer 4

Unguided (Wireless)

Question 5

Types of Transmission Lines

Answer 5

• Balanced

- Unbalanced

Question 6

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

Answer 6

Balanced Transmission Lines

Question 7

it has an advantage that most noise interference is induce equally in both wires, producing longitudinal currents that cancel in the load

Answer 7

Balanced Transmission Lines

Question 8

Example of Balanced Transmission Lines are

Answer 8

Parallel Conductor Transmission Lines

Question 9

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

Answer 9

Unbalanced Transmission Lines

Question 10

Example of Unbalanced Transmission Lines are

Answer 10

Coaxial Cable Transmission Lines

Question 11

current flows in opposite directions are known as

Answer 11

metallic circuit currents

Question 12

current flows in same directions are known as

Answer 12

longitudinal circuit currents

Question 13

balun stands for

Answer 13

balanced and unbalanced

- use to connect balanced and unbalanced transmission lines

Question 14

most common type of balun is

Answer 14

Narrowband Balun which is also known as choke , sleeve or bazooka

Question 15

balun has turns ratio of

Answer 15

4 : 1

Question 16

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 ).

Answer 16

Parallel Conductor Transmission Lines

Question 17

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

Answer 17

Open Wire Line

primary use : voice-grade telephone

Question 18

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)

Answer 18

Twin Lead

primary use : television to rooftop antenna

Question 19

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)

Answer 19

Twisted Pair : UTP and STP

primary use : Local Area Network because it is easy to install and inexpensive

Question 20

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

Answer 20

UTP - Unshielded Twisted Pairs

Question 21

the minimum number of twist for UTP is

Answer 21

Two Twist per Foot

Question 22

7 types of UTP according to EIA/TIA 568 Standard:

Answer 22

Level 1 , 2 , Category 3 ,4 ,5 Enhanced Category 5 and Category 6

Question 23

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

Answer 23

STP - Shielded Twisted Pair

Question 24

7 typer of STP according to EIA/TIA 568 Standard:

Answer 24

Category 3,4,5 Enhanced Category 5 , Category 7 , Foil Twisted Pair , and Shielded Foil Twisted Pair.

Question 25

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.

Answer 25

Crosstalk

Question 26

for twisted pair as category number increases

Answer 26

the number of twist also increases and also the information capacity

Question 27

UTP Connectors are:

Answer 27

RJ:(registerred jack) - 45 - 11

Question 28

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

Answer 28

Coaxial Cable

Question 29

types of coaxial cable:

Answer 29

- Rigid Air-Filled Coaxial Cable | - Solid Flexible Coaxial Cable

Question 30

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.

Answer 30

Rigid Air-Filled Coaxial Cable

Question 31

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).

Answer 31

Solid Flexible Coaxial Cable

Question 32

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

Answer 32

RG ( Radio Government )

Question 33

Coaxial Cable Connectors:

Answer 33

- BNC ( Bayonet Neil Concealman ) Connector | - N-Type Connector

Question 34

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

Answer 34

BNC

Question 35

it is threaded and must be screwed on and off

Answer 35

N-Type Connector

Question 36

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

Answer 36

Shielding

Question 37

coax with one layer of foil and one layer of braided shielding is known

Answer 37

Dual Shielding | there is also Quad Shielding which is two foil and two braided shielding

Question 38

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

Answer 38

electrical properties and physical properties

Question 39

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 )

Answer 39

Primary Constants | RL // RC - lumped parameters

Question 40

primary constants:

Answer 40

--series resistance and series inductance ohm/length and henry/length --shunt conductance and shunt capacitance siemen / length and farad / length

Question 41

parallel conductor transmission line | Series Inductance :

Answer 41

L=(u/pi) ln(2S/d) where : S= Separation or Distance between two Conductors

Question 42

parallel conductor transmission line | Series Capacitance :

Answer 42

C=(pi x e/ ln(2S/d) where: e=permittivity of medium d=diameter of inner diameter

Question 43

Coaxial Cable Transmission Line | Series Inductance :

Answer 43

L= (u/2pi) ln (D/d) where: D=inside diameter of the outer conductor

Question 44

parallel conductor transmission line | Series Capacitance :

Answer 44

C=2 pi e / ln (D/d) where: e=permittivity of medium d=diameter of inner diameter

Question 45

these are the transmission characteristics of a transmission lines:

Answer 45

Secondary Constant: - Characteristic Impedance - Propagation Constant

Question 46

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

Answer 46

Characteristic Impedance

Question 47

Characteristic Impedance Formula:

Answer 47

Zo = sqrt ( R + JwL / G + JwC )

Question 48

Characteristic Impedance Formula for RF / High Frequencies , R = G = 0

Answer 48

Zo = sqrt ( L/C ) ... Lucy Torres

Question 49

Characteristic Impedance Formula for Audio Frequencies / Low Frequencies , wL = wC = 0

Answer 49

Zo = sqrt (R/G) ... Richard Gomez

Question 50

Characteristic Impedance Formula for Parallel Conductor Transmission Lines :

Answer 50

Zo = ( 276 / sqrt(er) ) log (2S/d) er = relative permittivity d=diamter of inner conductor

Question 51

Characteristic Impedance Formula for Coaxial Cable Transmission Lines

Answer 51

Zo = ( 138 / Sqrt(er) ) log (D/d) er = relative permittivity D= inside diameter of the outer conductor d=diamter of inner conductor

Question 52

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

Answer 52

Propagation Constant: y = sqrt ( (R+JwL) (G+JwC) ) y = a + jB

Question 53

Attenuation Coefficient :

Answer 53

``` a = R / Zo a(np/m) = R / (2 x Zo) a(db/100ft) = 4.343 (R / Zo) ```

Question 54

Phase Shift Coefficient :

Answer 54

``` B = 360 / lambda = 2 pi / lambda B = w sqrt(LC) .... for High Frequency ```

Question 55

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.

Answer 55

Velocity Factor

Question 56

Velocity Factor Formula:

Answer 56

``` vf = vp / c vf = 1/sqrt (er) vf = 1/n ```

Question 57

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

Answer 57

Dielectric Constantc

Question 58

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

Answer 58

Delay Lines

Question 59

Time Delay :

Answer 59

td = Distance / Velocity

Question 60

Time Delay For 1 Meter :

Answer 60

td = sqrt (LC)

Question 61

Time Delay For 1 Foot

Answer 61

td = 1.016 sqrt(er)

Question 62

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

Answer 62

" transmission line behavior " : - physical length = 10km - length in terms of wavelength =0.25lambda - electrical length = 120degrees

Question 63

Transmission Line Losses

Answer 63

- Conductor Loss - Dielectric Heating Loss - Radiation Loss - Coupling Loss - Corona

Question 64

it is also known as "conductor heating loss" or "I^2R los", and it is directly proportional to the square of the length of the line and inversely proportional to the characteristic impedance. it is the inherent and unavoidable power loss because of the finite resistance of the transmission lines, and depends somewhat on frequency because of a phenomenon known as "skin effect"

Answer 64

Conductor Loss

Question 65

it is caused by a difference of potential between conductors in a metallic transmission line (ie., 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"

Answer 65

Dielectric Heating Loss

Question 66

if the separation between the conductors in a transmission line is an appreciable fraction of wavelength, the electrostatic and electromagnetic that surrounds the conductor caused 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"

Answer 66

Radiation Loss

Question 67

it occurs whenever a connection is made to or from a transmission line or when two section of transmission lines are connected together.

Answer 67

Coupling Loss

Question 68

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, and when this occurs , usually the transmission line is destroyed

Answer 68

Corona

Question 69

is a phenomenon wherein the signals tend to propagate at the outer edge of the cable if the frequency of the 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

Answer 69

Skin Effect

Question 70

it is also known as Flat Line or a Matched Line, wherein there is no reflected power in the transmission line a transmission line is a resonant line if it is a infinite length or if it is terminated with a resistive load equal to the ohmic value of the characteristic impedance of the transmission line

Answer 70

Non-Resonant Transmission Line: | Zo=Zl

Question 71

it is also known as a mismatched line, in which if the load impedance is not equal to characteristic impedance of the line 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

Answer 71

``` Resonant Transmission Line: Zo not equal to Zl ZL is Shorted ZL is Open ZL = R + jX ```

Question 72

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

Answer 72

``` Reflection Coefficient : r= Vref/Vinc r=Iref/Iinc r=sqrt(Pref/Pinc) r=ZL-Zo/Zl+Zo r= SWR-1/SWR+1 r= Vmax - Vmin / Vmax + Vmin r= Imax - Imin / Imax + Imin ```

Question 73

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 characteristic impedance

Answer 73

``` Standing Wave Ratio : VSWR = Vmax / Vmin ISWR = Imax / Imin SWR = ZL/Zo SWR = Zo/ZL SWR = Vinc + Vref / Vinc - Vref SWR = Iinc + Iref / Iinc - Iref SWR = 1 + r / 1 - r ```

Question 74

Typical Value:

Answer 74

r < 1 | SWR > 1

Question 75

Ideal Value:

Answer 75

``` r = 0 SWR = 1 ```

Question 76

Worst Case Value:

Answer 76

``` r = +1 or -1 SWR = Infinite ```

Question 77

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.

Answer 77

Standing Wave

Question 78

standing wave on an open circuited line

Answer 78

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 waveform is "minimum at open" the sum of incident and reflected voltage waveform is "maximum at open"

Question 79

standing wave on a short circuited line

Answer 79

the "voltage incident wave" is "reflected 180" degrees from how it woulds 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 waveform is "maximum at short" the sum of incident and reflected voltage waveform is "minimum at short"

Question 80

Absorbed Power by the Load :

Answer 80

``` Pabs = Pinc - Pref Pabs = Pinc ( 1 - r^2 ) Pabs = Pinc ( 4SWR / ( 1 + SWR )^2 ) ```

Question 81

Return Loss And Mismatch Loss:

Answer 81

``` RL = 1 / r^2 RL(db) = -20log(r) ```

Question 82

Mismatch Loss :

Answer 82

``` ML = 1 / 1-r ML(db) = -10log(1-r) ```

Question 83

Transmission Line Input Impedance:

Answer 83

Zin = Zo ( Zl + j Zo Tan(Bl ) / Zo + jZl Tan(Bl) )

Question 84

Matched Load : ZL=Zo

Answer 84

V ref = 0 , I ref = 0 , RL=0 , r = 0 , SWR = 0 VL = IL x ZL IL = VL / ZL Zin = Zo = ZL

Question 85

Short Circuited Load: ZL=Zo

Answer 85

``` VL = 0 V ref = -V inc Iref = I inc = IL /2 IL = I inc + I ref IL = 2 Iinc SWR = infinite Zin = jZo Tan (Bl) ```

Question 86

Open Circuited Load : Zl = infinite

Answer 86

``` V ref = V inc = Vl/2 I ref = -I inc VL = V inc + V ref VL = 2 V inc IL = 0 r = 1 ```

Question 87

Traveling waves that are coming from the transmitter.

Answer 87

Incident Waves

Question 88

Traveling waves that are brought back to the transmitter due to unmatched line

Answer 88

Reflected Waves

Question 89

For A Maximum Power Transfer from source to load

Answer 89

a transmission line must be terminated in a purely resistive load equal to the characteristic impedance of the transmission line.

Question 90

vector quantity

Answer 90

reflection coefficient

Question 91

scalar quantity

Answer 91

standing wave ratio

Question 92

the behavior of transmission line depends on its:

Answer 92

Length And Termination

Question 93

when a transmission line is terminated in either short or open circuit, there is an :

Answer 93

impedance inversion in every quarter-wavelength

Question 94

transmission lines that are terminated by either a short or an open circuit can be used as:

Answer 94

REACTANCES or as either SERIES or PARALLEL RESONANTS CIRCUITS depending on their length

Question 95

at UHF and Microwave Frequencies where one-half wavelenght is less than 1 foot :

Answer 95

transmission lines are commonly used to replace conventional LC Tuned Circuits

Question 96

it is a section of a transmission line, electrically a quarter-wavelenght in the length that is used to match a transmission line to a purely resistive load whose resistance is not equal to the characteristic of the line

Answer 96

Quarter Wave Transformer

Question 97

Impedance Of Quarter Wavelength Transformer:

Answer 97

Zo(lambda/4) = sqrt ( Zo x ZL )

Question 98

the quarter wave transformer act as a transformer with :

Answer 98

1:1 turns ratio Zo = ZL a = 1

Question 99

the quarter wave transformer acts as a step-down transformer when :

Answer 99

ZL > Zo | a > 1

Question 100

the quarter wave transformer acts as a step-up transformer when :

Answer 100

ZL < Zo | a < 1

Question 101

it is a short section of line, usually short-circuited at one end that is used for impedance matching, and it is placed across the primary line as close to the load as possible it is used to remove (cancel) the reactive component of the complex impedance of the load and to match it to the transmission line

Answer 101

Stub

Question 102

Types of Stub matching :

Answer 102

- Series Open Stub - Series Short Stub - Shunt Open Stub - Shunt Short Stub

Question 103

Shorted Stubs are preffered because Open Stubs ?

Answer 103

Have tendency to radiate , especially at higher frequencies

Question 104

if the load is inductive

Answer 104

the capacitive stub is used

Question 105

if the load is capacitive

Answer 105

the inductive stub is used

Question 106

is used to match a resistive load while stub is used to match a complex or reactive load

Answer 106

the quarter wave transformer

Question 107

is used to match a complex or reactive load

Answer 107

stub

Question 108

it is used to measure the power being delivered to a load or an antenna through a transmission line, moreover , it allows the measurement of power moving along the line in each direction thus it is possible to measure incident and reflected power separately

Answer 108

Directional Coupler

Question 109

it is used to measure standing waves ; TDR ( Time Domain Reflectometry) it is a technique that can be used to locate an impairement in a metallic cable

Answer 109

Reflectometer

Question 110

in TDR,

Answer 110

a step input or pulse is applied to the input of a transmission line ; by examining the reflected signal , much information can be gained about such things as the length of the line , the way in which it is terminated, and the type and location of any impedance discontinuities on the line.

Question 111

it is a short section of air-dielectric coaxial line, with a slot in the outer conductor through which a probe is inserted; the probe does not actually touch the inner conductor , it is CAPACITIVELY COUPLED , so as to disturb the signal on the line as little as possible it permits convenient and accurate measurement of standing waves

Answer 111

SLOTTED LINE

Question 112

it is the graphical calculator, created and developed by Phillip Smith , used for transmission line matching it is a polar impedance diagram which consist of two sets of circles or arc of circles, which are so arranged that various important quantities connected with mismatched transmission line may be plotted and evaluated fairly easily

Answer 112

Smith Chart

Question 113

at low frequencies

Answer 113

Standard Transmission Lines would be too long fro practical use as reactive components or tuned circuits

Question 114

for high frequency applications,

Answer 114

special transmission lines consctructed with copper patterns on a PCB have been developed to interconnect components on PC boards.

Question 115

these are two printed circuit board implementations of transmisison lines known as _____ and ______are widely used to Create Resonant Circuits and Filters

Answer 115

STRIPLINES , MICROSTRIP

Question 116

it is a flat conductor separated from a ground plane by insulating dielectric material. its characteristic impedance is dependent on its physical characteristics it has advantage over stripline in being simpler construction and easier integration with semiconductor devices, tending itself well to printed circuit and thin film techniques

Answer 116

Microstrip

Question 117

Microstrip Characteristic Impedance :

Answer 117

Zo = ( 87 / sqrt(er + 1.41 ) ) ln (5.98h / 0.8w + t )

Question 118

it is a flat conductor sandwiched between two ground planes. it is more difficult to manufacture than microstrip, but it is less likely to radiate; thus losses in stripline are lower than microstrip

Answer 118

Stripline

Question 119

Stripline Characteristic Impedance :

Answer 119

Zo = ( 60 / sqrt(er) ) ln ( 4d / ( 0.67pi x w ) ( 0.8 + t/h ) )