transmission lines lecture 01

7/31/2019 Transmission Lines Lecture 01

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ECEn513 Lecture # 1

Transmission Lines

Ramel E. Recentes

La Salle University


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Introduction

Transmission Media can be generally

categorized as either

guided

unguided


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Guided media are those with some form ofconductor that forms a conduit between Tx and Rx.Unguided media include free space, air or even

water.

Guided Media can be further be categorised as

transmission lines or metallic cables

optical fibers


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A transmission lineis a metallic conductor

system used to transfer electrical energy from

one point to another. It is made up of 2 or more

electrical conductors separated by insulator.

When propagating signals at DC or low

frequencies the behaviour of TL is predictable.

However, at high frequencies it becomescomplex.


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Wave Basics

Types of waves

1. longitudinal waves the displacement

(amplitude) is in the direction of propagation.Examples: water waves, sound wave

2. transverse waves the direction of displacementis perpendicular to the direction of propagation.

Ex. TEM


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TEM (Transverse Electromagnetic Waves) are

waves consisting of electric and magnetic

components. Transmission of power along a TL

is in the form of TEM.

The TEM propagates primarily in the dielectric

part.


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In conductors, current and voltage are always

accompanied by an electric ( E) field and a

magnetic (H) field.

Electromagnetic waves that travel from sourceto load are called incident waves. Waves that

travel back are referred to as reflected waves.


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The Transverse Electromagnetic Wave


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Wave Velocity, Frequency and

Wavelength

Wave Velocity speed of TEM waves along a certainmedium.

Light Speed = 186.283 miles/ sec or 299,793,000 m/s

TEM waves travel slightly slower depending on thedielectric used. But generally it is approximated at

3 X 108

Frequency The rates at which the wave repeats

Wavelength The distance of one cycle.


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A wave


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Examples:

1. Calculate the wavelength of a wave with

frequency of 145Mhz.

2. Determine the frequency for electromagnetic

waves with wavelengths 1cm and 10m.


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Types of Transmission Lines

balanced

unbalanced


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Balanced Transmission Line

With two wire balanced transmission lines , both

conductors carry current; however , one conductorcarries the signal and the other is the return path.

Unbalanced Transmission Line

With unbalanced transmission line, one wire is atground potential, whereas the other wire is atsignal potential.


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Figure A . Differential or Balanced Transmission Line


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Figure A : Single ended or unbalanced transmission system


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Balun- A circuit device used to connect a

balanced transmission line to unbalanced

transmission line (balanced to unbalanced)

Examples of balun

transformer balun

bazooka balun or choke /sleeve


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Transformer Balun


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Metallic Transmission Lines

Standard metallic transmission lines can either

be :

Parallel Conductor TL

Coaxial (Concentric) TL


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Parallel Conductor TL are comprised of two or

more metallic conductors (usually copper)

separated by a nonconductive insulating

material called dielectric. Dielectrics canbe air, rubber, polyethylene, paper, mica,

glass, and Teflon.


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Common types

open wire TL

twin lead

twisted pair ( includes UTP or unshielded

twisted pair and STP or shielded twisted pair)


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Open Wire Transmission Line


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Twin Lead Transmission Line


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Twisted Pair Transmission Line


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EIA/TIA 568 UTP and STP levels and

Categories

UTP Unshielded twisted pair (100 ohms)

STP Shielded twisted pair (150 ohms)

Size of twisted pair varies from 16AWG to 26AWG.

Standards cable varies from 22AWG to 24AWG.

Minimum number of twists is 2 per foot.


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EIA/TIA 568 UTP and STP levels and

Categories


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Cat 5 cable

Most commonly used in todays local areanetworks

Comprised of 4 pairs of wires 2 are unused.

Pair 1 : blue/white stripe and blue

Pair 2 : orange/white stripe and orange

Pair 3 : green/white stripe and green

Pair 4 : brown/white stripe and brownCan be Cat5 flex or Cat5 solid

An improved version is CAT5E (enhanced)


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Proposed new categories


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Cat 5 cable


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Plenum Cable

a cable that is laid in the plenum spaces of

buildings. The plenum is the space that can

facilitate air circulation for heating and air

conditioning systems, by providing pathwaysfor either heated/conditioned or return

airflows.

A plenum type cable meets thermalrequirements to be used in the plenum.


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Coaxial Cables


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Coaxial Cables

Basic Types

(a)rigid air field

(b)solid flexible


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RG series cables (RG = Recommended

Guide)


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Coaxial cable Connectors

BNC Connector

BNC Barrel

BNC T

Type N

Type N barrel


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BNC Connector


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BNC Barrel


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BNCT


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Type N connector


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Type N Barrel


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Assignment

Choose a specific cable number ( parallel or

coaxial) and do the following:

(a) Secure a sample (at least 1 meter long)

(b) Research the specification

(c) Identify the common uses(d) Bring your cable and prepare a short

presentation for b and c.


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End of Part 1


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Now the engineering part.

transmission lines lecture 01

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