antennas , wave propagation &tv engg

8/12/2019 Antennas , Wave Propagation &Tv Engg

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ANTENNAS & WAVE PROPAGATION

BY:

Deepti ChaharAstt. Professor

DRONACHARYA COLLEGE OF ENGG.


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SYLLABUS SECTION A :

Retarded potential, field of short dipole, antenna pattern andantenna parameters, Gain, Directivity, Radiation resistance,

aperture, beam-width etc, reciprocity theorem for antenna .

SECTION B:Wave Eq for radiated fields from current and voltage sources in

terms of electric scalar potential and magnetic vector potential.Fields and pattern of an infinite small dipole. Definition of

various potentials used in antenna


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Relationship between current distribution and field pattern of anantenna, linear antenna, halfwave dipole, antenna impedance,directivity, radiation resistance, directional properties, effect ofground on antenna pattern, input impedance , broad bandmatching.

SECTI ON C:

two element array, broad side, end fired pattern, beam width pattern multiplication, multi element array and their properties,synthesis of an array, parabolic feed antenna, conical , helix,log periodic horn. Microwave , gndwave, sky wave

propagation .


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SECTION D:

Picture transmission, sound transmiision, picture receptio,sound reception synchronisation, receiver cntrols, color tv.Monochrome picture tube, beam deflection, screen phosphor,face plate, picture tube characteristics, picture tube, circuitscontrols. Tv camera tubes: basic principla. Image orthicon.Vidicon.

Books

1. Antenna and Wave Propagation by K.D Prasad.2. Antennas By: J.D Krauss.


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Antenna Definition

An antenna is an electrical conductor or system of ELEVATEDconductors

Transmission - radiates electromagnetic energy into space

Reception - collects electromagnetic energy from space


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What is an antenna?

Region of transition between guided and free space propagation

Launches waves from a guiding structure into space or air(transmitting case)

Not limited to electromagnetic waves (e.g. acoustic waves)


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Transition from guided wave to free space wave


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Polytechnic University 2002 by H. L. Bertoni 9

Antennas Radiate Electromagnetic Waves

EM waves have: Electric field E (V/m)

Magnetic field H (A/m) E and H

Perpendicular to each other andto direction of propagation

Amplitude depends on direction

of propagation - Radiation Pattern

TransmittingAntenna

Cable

E

H


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Radiation Mechanism


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Antennas Transmission line uses

conductor to carry voltage &

current

Radio signal travels through air

(insulator )

Antennas are transducers

- convert voltage & current into

electric & magnetic field

-bridges transmission line & air- similar to speaker/microphone

with acoustic energy.

Transmission Line Voltage & current variations

produce EM field around conductor

EM field expands & contracts atsame frequency as variations

EM field contractions return energto the source (conductor)

Nearly all the energy in thetransmission line remains in the

system.


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Types of Antennas

Wire antennas Aperture antennas

Array antennas Reflector antennas Lens antennas Patch antennas


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Aperture antennas


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Patch antennas


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Array antennas


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Log Periodic Dipole Array


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Antenna Basics

High Frequency1.6 - 30 Mhz + 50 Mhz

160 - 6 metres

An antennas size/length depends on the frequency Its functionality largely depends on the height aboveground, as well as the polarity and its configuration


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Types of Antennas

1. Isotropic antenna (idealized)1. Radiates power equally in all directions

2. Dipole antennas1. Half-wave dipole antenna (or Hertz antenna)2. Quarter-wave vertical antenna (or Marconi

antenna)

3. Directional Antennas4. Reflective Antenna


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Omnidirectional Antennas


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Parabolic Reflector Antenna


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Isotropic Radiators

An isotropic antenna is one which radiates equally inall directions .

If the total power radiated by the isotropic antenna is P , then

the power is spread over a sphere of radius r ,so that thepower density S at this distance in any direction is given as:


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Half-wave Dipole (Hertz) Antenna

An antenna having a physical length that is one-halfwavelength of the applied frequency is called aHertz antenna

or a half-wave dipole antenna. Hertz antennas are not found at frequencies below

2MHz because of the physical size needed of the

antenna to represent a half-wave


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The Antenna Formula

c 186,000 mi sec

c is the speed of light is the wavelength of the signal use 3 x 10 8 when dealing in meters for the speed of light

frequency of the signal


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The Antenna Formula - applied

If a half-wave dipole antenna needed to beconstructed for a 60 Hz signal, how largewould it need to be?

c 186,000 mi sec

60= 3100 mi

2 = 1550 miles!


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Antenna Parameters

All antenna have important parameterscommon to all types of antenna irrespective oftype of application listed below :

Radiation pattern Radiation Power Density Radiation Intensity Gain, Directive gain


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Antenna Parameters(cont) Directivity, Power Gain Antenna Efficiency Effective Apperture Radiation Resistance

Antenna Bandwidth Antenna Beam width Polarization Antenna Temperature Self Impedance Mutual Impedance

antennas , wave propagation &tv engg

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