ANTENNA AND ITS FUNDAMENTAL REPORT

Antenna Fundamentals and its applications

Department of Electronics and Communication

CHAPTER: 1

INTRODUCTION



1. Introduction:-

1.1. Introduction to Doordarshan:-

In November, 1982 DD replay center with 100W transmitter was started. 28th

November, 1982 marked the start of DD1 10KW HPT with BEL transmitter. The

installation and commissioning of studio took place in may, 2000. Commissioning of

10kW (Thom cast) DD2 transmitter (DD news) was done on 3rd July, 2000.

January.2004 marked the starting of 30min local transmission (narrowcasting).

Replacement of DD1 BEL transmitter with 10kW ROHDE and SCHWARZ

transmitter was done on 18thjuly, 2005. Finally starting of additional 30 minutes local

transmission came into effect from 3rd September, 2007.

DD NATIONAL

DD NATIONAL is commissioned from 28th November, 1984. The primary coverage

area is 65 to 70 kilometers. The cost of transmitter is Rs. 1, 10, 87,854.

DD NEWS

DD NEWS is started from 3rd July, 2000. The coverage area is around 65 to 70

kilometers radial. The cost of transmitter is Rs. 1, 95, 01,167.

1.1.1. Studio:-

Finally the studio is established in May, 2000. The floor area is around 14mtrs. The

height of studio is 7.5mts. Three studio cameras, 16 channels for vision mixer and

eight channels for audio mixer are used. The total land area of DDK, Indore is 3.31

areas. In this total constructed area is 2364 square meter. The plot number is 114. The

state government provided the land for free on 28th March,1984. The latitude and

longitude is 22deg.42min.02sec and 75deg.52min.48sec respectively. The height

from mean sea level is 550m.



1.1.2. Mast:-

The height of the tower is 150m. the year of erection is of the tower is 28th January,

1985. The height of platform is 40m, 75m, 104m, 125m. The antenna used is stacked

dipole (wideband,24 panels,6 panel per size). The other antenna used as AIR FM,

IGNOV FM (FM channel at heights 104meters).

1.2 Introduction to Antenna:-

An antenna is a device for converting electromagnetic radiation in space into

electrical currents in conductors or vice-versa, depending on whether it is being used

for receiving or for transmitting, respectively. Passive radio telescopes are receiving

antennas. It is usually easier to calculate the properties of transmitting antennas.

Fortunately, most characteristics of a transmitting antenna (e.g., its radiation pattern)

are unchanged when the antenna is used for receiving, so we often use the analysis of

a transmitting antenna to understand a receiving antenna used in radio

astronomy. First radio antenna was assembled in 1886 by Heinrich Hertz. He

developed a circuit resembling a radio system with end loaded dipoles as a

transmitting antenna while resonant square loop antenna as a receiving antenna

operating at one meter wavelength. The laboratory work done by Hertz was further

completed by Guglielmo Marconi and in 1901; he demonstrated world

communication of signal over long distances. Thus Hertz and Marconi are the

pioneers of antenna.

A RF antenna is defined as a component that facilitates the transfer of a guided wave

into, and the reception from, free space. In function, the antenna is essentially a

transducer that converts alternating currents into electromagnetic fields or vice versa.

The physical components that make up an antenna’s structure are called elements.

From a coat hanger to a tuned Yagi, there are literally hundreds of antenna styles and

variations that may be employed. Receive and transmit antennas are very alike in

characteristics and in many cases are virtual mirror images of each other. However, in



many Part 15 applications it is advantageous to select different characteristics for the

transmitter and receiver antennas. For this reason, we will address each separately.

According to the strict definition of an antenna as a device for converting between

electromagnetic waves in space and currents in conductors, the only antennas in most

radio telescopes are half-wave dipoles and their relatives, quarter-wave ground-plane

verticals. The large parabolic reflector of a radio telescope serves only to focus plane

waves onto the feed antenna. [The term "feed" comes from radar antennas used for

transmitting; the "feed" feeds transmitter power to the main reflector. Receiving

antennas used in radio astronomy work the other way around, and the "feed" actually

collects radiation from the reflector.]

The Transmitter Antenna:-

The transmitter antenna allows RF energy to be efficiently radiated from the output

stage into free space. In many modular and discrete transmitter designs, the

transmitter’s output power is purposefully set higher than the legal limit. This allows

a designer to utilize an inefficient antenna to achieve size, cost, or cosmetic objectives

and still radiate the maximum allowed output power. Since gain is easily realized at

the transmitter, its antenna can generally be less efficient than the antenna used on the

receiver.

The Receiver Antenna:-

The receiving antenna intercepts the electromagnetic waves radiated from the

transmitting antenna. When these waves impinge upon the receiving antenna, they

induce a small voltage in it. This voltage causes a weak current to flow, which

contains the same frequency as the original current in the transmitting antenna. A

receiving antenna should capture as much of the intended signal as possible and as

little as possible of other off-frequency signals. Its maximum performance should be

at the frequency or in the band for which the receiver was designed. The efficiency of

the receiver’s antenna is critical to maximizing range performance. Unlike the

transmitter antenna, where legal operation may mandate a reduction in efficiency, the

receiver’s antenna should be optimized as much as is practical. Actual half-wave

dipoles, backed by small reflectors about quarter wavelength behind them to focus the



dipole pattern in the antenna are almost unidirectional. There is a back lobe which can

be reduced by placing elements close to each other. The folded dipole element

resonates at a frequency of resonance but reflector resonates at a frequency lower

than resonant frequency while director resonates at a frequency greater than resonant

frequency.

1.2.1. Types of Antenna:-

Yagi-Uda Antenna:-

The Yagi-Uda antenna consists of folded dipole as driven element along with

reflector and one or more directors. The director and reflectors are straight conductors

which are called parasitic element. The directors are placed in front of driven

elements while the reflector is placed behind the driven element. The length of folded

dipole is half the wavelength while length of director is less than half the wavelength

and that of reflector is greater than half the wavelength. The radiation pattern of the

Yagi-Uda antenna is almost unidirectional. There is a back lobe which can be reduced

by placing elements close to each other. The folded dipole element resonates at a

frequency of resonance but reflector resonates at a frequency lower than resonant

frequency while director resonates at a frequency greater than resonant frequency

Advantages of Yagi-Uda Antenna:

1) It has excellent sensitivity.

2) Its front to back ratio is excellent.

3) It is useful as receiving antenna at high frequency for TV reception.

4) It has almost unidirectional pattern.

5) It is broadband antenna.

Lens Antenna:-

A lens antenna is an antenna consisting an electromagnetic lens with a feed. In other

words, it is a three dimensional electromagnetic device having refractive index n

other than unity. Its operation is similar to a glass lens used in optics. The lens

antenna can be used in transmitting mode and in receiving mode both. Advantages of

lens Antenna:



1) In lens antenna, the rays are transmitted away from the feed system; hence the

aperture is not obstructed due to feed and feed support.

2) In lens antenna, as the wave enters from one side end leaves out from other end,

greater extent of wrapping and twisting is possible without disturbing electrical

path length.

3) Lens antenna can be used to feed at a point off the axis, so it is most extensive

used in the applications where beam is needed to be moved angularly with respect

to axis.

Turnstile Antenna:-

The turnstile Antenna is formed by placing two half wave dipoles perpendicular to

each other. These dipoles are excited such that the currents are equal in magnitude but

in phase quadrature. The radiation pattern produced is almost unidirectional. The

Turnstile antenna is useful to match 70 ohms dual coaxial line to increase directives

an array of turnstile antennas is used.

Long-wire Antenna:-

The antennas which operate between frequency ranges of 3-30 MHz are called High-

Frequency antennas .For the HF band, the wavelength ranges in 100 -10 meters the

HF antennas can be made in size comparable with the wavelength. The directional

properties can also be obtained for such antennas. In case of Low frequency band and

Mid frequency band, the wavelength is greater, the size of antenna becomes larger

and it becomes difficult to achieve highly directional system.



CHAPTER: 2

DESCRIPTION ABOUT THE

INDUSTRIAL TRAINING



2. Description about the industrial training:-

2.1 Theoretical considerations:-

2.1.1. Various Sections of Doordarshan:-

Studio

Mast

Antenna

Transmitters

Earth Station

CAR

ENG

Video Tape recorders

Computer Section

Non-linear editing

OB-VAN

DSNG

Video chain of OB VAN

Studio:-

Finally the studio is established in may,2000. The floor area is around 14mtrs. The

height of studio is 7.5mts. Three studio cameras, 16 channels for vision mixer and

eight channels for audio mixer are used. The total land area of DDK, Indore is 3.31

area. In this total constructed area is 2364 square meter. The plot number is 114. The

state government provided the land for free on 28th March,1984. The latitude and

longitude is 22deg.42min.02sec and 75deg.52min.48sec respectively. The height

from mean sea level is 550m.

Mast:-

The height of the tower is 150m. the year of erection is of the tower is 28th January,

1985. The height of platform is 40m, 75m, 104m, 125m. The antenna used is stacked



dipole (wideband,24 panels,6 panel per size). The other antenna used as AIR FM,

IGNOV FM (FM channel at heights 104meters). An antenna is a device for

converting electromagnetic radiation in space into electrical currents in conductors or

vice-versa, depending on whether it is being used for receiving or for transmitting,

respectively. Passive radio telescopes are receiving antennas. It is usually easier to

calculate the properties of transmitting antennas. Fortunately, most characteristics of a

transmitting antenna (e.g., its radiation pattern) are unchanged when the antenna is

used for receiving, so we often use the analysis of a transmitting antenna to

understand a receiving antenna used in radio astronomy.

Transmitters DD-I & DD-II:-

The 10KW TV Transmitter NEC for DD-I is being radiated on 150 Meter Mast

having two panels and at present both panels are working satisfactory.

The 10 KW TV Transmitter NEC make for DD-II NEWS is being radiated on 10

KW power and the antenna is installed on same 150 meter mast of DDI. The

antenna for 10 KW power is under installation.

The two Numbers of Diesel Generators set 63KVA each has been provided for dd-I

and DD-II for standby power supply and both are working satisfactory.

For the reception of the programs for DD-I and DD-II NEWS Digital Receivers

(IRD) has been provided. Since this year we also received the KU band equipments

for monitoring as well as used for both the transmitters and the quality of signal is

very good.

The Details of 10 KW Transmitter of DDK is given below:



Table 1. Technical Specifications of Transmitter for DD-I

Transmitter Make NEC-VHF

Transmitter type PCN 1610 SSPH/1

Band of Operation Band-III

Channel for operation CH-6(-)

Channel Frequency (vision) 182.25 M Hz

Channel Frequency (Audio) 187.75 M Hz

Date of Commission as HPT 30th August 1984

Date of Replacement of Transmitter 10th July 2003



Table 2. Technical Specifications of Transmitter for DD-II

Transmitter Make NEC-UHF

Transmitter type PCN 1110 SSP/1

Channel for operation CH-28(-)

Channel Frequency (vision) 527.25 M Hz

Channel Frequency (Audio) 532.75 M Hz

Date of Commission as HPT 18th August 2002

CAR :-

CAR This stands for central apparatus room. Car is basically a channel or path

through which the video signal passes. All studio has its own CCU i.e. camera

control unit. PCR i.e. panel control room The no. or model of video console is PDS



ENG:-

ENG stands for electronic news gathering. The purpose of eng is to gather news from

different outside locations. Cameras used in eng section are small and light weight.

These cameras are called camcorders.

Video Tape recorders:-

Video Tape recorders VTR room is provided at each studio center. It houses at least

two console type 1”videotape recorders (VTRs) and a few Broadcast standard

Videocassette recorders (VCRs). In these recorders, sound and video signals are

recorded simultaneously on the same tape.

Computer Section:-

Computer Section It is basically related to editing. There are two types of editing’s.

Linear editing. Non linear editing. Software used in non-linear editing. For news

editing Velocity 6.0 is used. For graphics MOV CG 2003 n Adobe Photoshop. For

program editing velocity 8.0 and FCP (final cut pro)

Non-linear editing:-

Non linear editing Problem with Linear Editing is sequential – first shot first Long

hours spent on rewinding of tapes , search of material Potential risk of damage to

original footage Difficult to insert a new shot in an edit Difficult to experiment with

Variations Quality loss more in analog; even with digital Limited Compositing,

effects, color correction Capability

NLE:-

NLE is video editing in digital format with standard computer based technology

Computer technology is harnessed in Random access, computational and

manipulation capability, multiple copies, intelligent search, sophisticated project and

media management tools, standard interfaces, and powerful display .

OB-VAN:-

OB-VAN It is known as outdoor broadcasting van and used for outer coverage.

Events like sports, functions are covered by this van. It consists of 8 cameras and 3



external sources and 4 VTR. LSM-LIVE SLOW MOTIN MACHINE. It is used to

play the replays in slow motion. There are also pc racks, mixers racks.

DSNG:-

This is known as direct satellite news gathering. It works simultaneously with OB

van. It’s also called as mobile earth station. The dish can be aligned acc to the

requirement. Monitors are available in this van to check the telecast. High power ups

are also available in this van.

Video chain of OB VAN:-

Video chain of OB VAN Output from the switcher goes to stabilizing amplifier via

PP and VDAs. Output from the stab. Is further distributed to various destinations. It

may be noted that the use of VDAs helps to monitor the video signal at different

locations and the use of PP is very helpful for emergency arrangements during

breakdowns and trouble shooting. A separate monitoring bus is provided in CCU,

LCU and END CONTROL with sources as. END CONTROL also has a remote for

the adjustment of levels etc. in the STAB AMP unit. R out for the other sources is

similar to this and can be understood from the block schematic



2.2 Material and methods:-

2.2.1 Some fundamentals of antenna:-

Radiation pattern

Radiation intensity

Directive gain and directivity

Power gain

Antenna beam width

Antenna bandwidth

Antenna input impedance

Effective aperture

Antenna temperature

Antenna polarization

Radiation pattern:-

Fig. 1 Radiation pattern

http://en.wikipedia.org/wiki/File:Sidelobes_en.svg



The radiation pattern of an antenna is a plot of the relative field strength of the radio

waves emitted by the antenna at different angles. It is typically represented by a three

dimensional graph, or polar plots of the horizontal and vertical cross sections. The

pattern of an ideal isotropic antenna, which radiates equally in all directions, would

look like a sphere. Many non-directional antennas, such as monopoles and dipoles,

emit equal power in all horizontal directions, with the power dropping off at higher

and lower angles; this is called an omnidirectional pattern and when plotted looks like

a doughnut. The radiation of many antennas shows a pattern of maxima or "lobes" at

various angles, separated by "nulls", angles where the radiation falls to zero. This is

because the radio waves emitted by different parts of the antenna typically interfere,

causing maxima at angles where the radio waves arrive at distant points in phase, and

zero radiation at other angles where the radio waves arrive out of phase. In

a directional antenna designed to project radio waves in a particular direction, the

lobe in that direction is designed larger than the others and is called the "main lobe".

The other lobes usually represent unwanted radiation and are called "side lobes". The

axis through the main lobe is called the "principal axis" or "bore sight axis".

Radiation intensity:-

The radiation intensity is defined as power per unit solid angle. It is expressed in

W/Sr (watts/Steradian). A solid angle is a section of the surface of the imaginary

sphere around the antenna. Unlike power density, radiation intensity does not depend

on distance: because radiation intensity is defined as the power through a solid angle,

the decreasing power density over distance (i.e. over of the imaginary sphere

around the antenna) due to the inverse-square law is offset by the increasing area of

the solid angle due to the same law. Therefore, power density can be converted to

radiation intensity by multiplying it with .

Directive gain and directivity:-

The directive gain is defined as the ratio of power density to the average power

radiated. An isotropic antenna is the omnidirectional antenna. The meaning of the

omnidirectional antenna is the antenna acting as a point radiator which radiates

equally in all directions. Directive gain of isotropic antenna is unity. Directive gain

http://en.wikipedia.org/wiki/Isotropic_radiator

http://en.wikipedia.org/wiki/Sphere

http://en.wikipedia.org/wiki/Monopole_antenna

http://en.wikipedia.org/wiki/Dipole_antenna

http://en.wikipedia.org/wiki/Null_(radio)

http://en.wikipedia.org/wiki/Interference_(wave_propagation)

http://en.wikipedia.org/wiki/Out_of_phase

http://en.wikipedia.org/wiki/Directional_antenna

http://en.wikipedia.org/wiki/Sidelobe

http://en.wikipedia.org/wiki/Antenna_boresight



can be defined as a measure of the concentration of the radiated power in a particular

direction. Directivity or maximum directive gain of an antenna is defined as the ratio

of maximum radiation intensity to its average radiation intensity.

Power gain:-

Gain is a parameter which measures the degree of directivity of the antenna's

radiation pattern. A high-gain antenna will preferentially radiate in a particular

direction. Specifically, the antenna gain, or power gain of an antenna is defined as the

ratio of the intensity (power per unit surface) radiated by the antenna in the direction

of its maximum output, at an arbitrary distance, divided by the intensity radiated at

the same distance by a hypothetical isotropic antenna. The gain of an antenna is a

passive phenomenon - power is not added by the antenna, but simply redistributed to

provide more radiated power in a certain direction than would be transmitted by an

isotropic antenna. An antenna designer must take into account the application for the

antenna when determining the gain. High-gain antennas have the advantage of longer

range and better signal quality, but must be aimed carefully in a particular direction.

Low-gain antennas have shorter range, but the orientation of the antenna is relatively

inconsequential. For example, a dish antenna on a spacecraft is a high-gain device

that must be pointed at the planet to be effective, whereas a typical Wi-Fi antenna in a

laptop computer is low-gain, and as long as the base station is within range, the

antenna can be in any orientation in space. It makes sense to improve horizontal range

at the expense of reception above or below the antenna. In practice, the half-wave

dipole is taken as a reference instead of the isotropic radiator. The gain is then given

in dBd (decibels over dipole). 0 dBd = 2.15 dBi. It is vital in expressing gain values

that the reference point be included. Failure to do so can lead to confusion and error.

Antenna beam width:-

Antenna beam width is the measure of the directivity of the antenna. The antenna

beam width is an angular width in degrees. It is measured on a radiation pattern on

major lobe. Antenna beam width is defined as the angular width in degrees between

the two points on a major lobe of a radiation pattern where the radiated power

decreases to half of its maximum value. The beam width is also called 3db beam

http://en.wikipedia.org/wiki/Antenna_gain

http://en.wikipedia.org/wiki/Intensity_(physics)

http://en.wikipedia.org/wiki/Isotropic_radiator

http://en.wikipedia.org/wiki/Wi-Fi



width as reduction of power to half of its maximum value corresponds to a reduction

of power expressed in dB by 3db.

Antenna bandwidth:-

Although a resonant antenna has a purely resistive feed-point impedance at a

particular frequency, many (if not most) applications require using an antenna over a

range of frequencies. An antenna's bandwidth specifies the range of frequencies over

which its performance does not suffer due to a poor impedance match. Also in the

case of a Yagi-Uda array, the use of the antenna very far away from its design

frequency reduces the antenna's directivity, thus reducing the usable bandwidth

regardless of impedance matching. Except for the latter concern, the resonant

frequency of a resonant antenna can always be altered by adjusting a suitable

matching network. To do this efficiently one would require remotely adjusting a

matching network at the site of the antenna, since simply adjusting a matching

network at the transmitter (or receiver) would leave the transmission line with a

poor standing wave ratio. Instead, it is often desired to have an antenna whose

impedance does not vary so greatly over a certain bandwidth. It turns out that the

amount of reactance seen at the terminals of a resonant antenna when the frequency is

shifted, say, by 5%, depends very much on the diameter of the conductor used. A

long thin wire used as a half-wave dipole (or quarter wave monopole) will have a

reactance significantly greater than the resistive impedance it has at resonance,

leading to a poor match and generally unacceptable performance. Making the element

using a tube of a diameter perhaps 1/50 of its length, however, results in a reactance

at this altered frequency which is not so great, and a much less serious mismatch

which will only modestly damage the antenna's net performance. Thus rather thick

tubes are typically used for the solid elements of such antennas, including Yagi-Uda

arrays.

Antenna input impedance:-

As an electro-magnetic wave travels through the different parts of the antenna system

(radio, feed line, antenna, and free space) it may encounter differences in impedance

(E/H, V/I, etc.). At each interface, depending on the impedance match, some fraction

http://en.wikipedia.org/wiki/Bandwidth_(signal_processing)

http://en.wikipedia.org/wiki/Yagi-Uda

http://en.wikipedia.org/wiki/Standing_wave_ratio



of the wave's energy will reflect back to the source, forming a standing wave in the

feed line. The ratio of maximum power to minimum power in the wave can be

measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A

SWR of 1.5:1 is considered to be marginally acceptable in low power applications

where power loss is more critical, although an SWR as high as 6:1 may still be usable

with the right equipment. Minimizing impedance differences at each interface

(impedance matching) will reduce SWR and maximize power transfer through each

part of the antenna system. Complex impedance of an antenna is related to

the electrical length of the antenna at the wavelength in use. The impedance of an

antenna can be matched to the feed line and radio by adjusting the impedance of the

feed line, using the feed line as an impedance transformer. More commonly, the

impedance is adjusted at the load (see below) with an antenna tuner, a balun, a

matching transformer, matching networks composed of inductors and capacitors, or

matching sections such as the gamma match.

Effective aperture:-

The effective area or effective aperture of a receiving antenna expresses the portion of

the power of a passing electromagnetic wave which it delivers to its terminals,

expressed in terms of an equivalent area. For instance, if a radio wave passing a given

location has a flux of 1 pW / m2 (10−12 watts per square meter) and an antenna has an

effective area of 12 m2, then the antenna would deliver 12 pW of RF power to the

receiver (30 microvolts rms at 75 ohms). Since the receiving antenna is not equally

sensitive to signals received from all directions, the effective area is a function of the

direction to the source. Due to reciprocity (discussed above) the gain of an antenna

used for transmitting must be proportional to its effective area when used for

receiving. Consider an antenna with no loss, that is, one whose electrical efficiency is

100%. It can be shown that its effective area averaged over all directions must be

equal to λ2/4π, the wavelength squared divided by 4π. Gain is defined such that the

average gain over all directions for an antenna with 100% electrical efficiency is

equal to 1. Therefore the effective area Aeff in terms of the gain G in a given direction

is given by:

http://en.wikipedia.org/wiki/Standing_wave_ratio

http://en.wikipedia.org/wiki/Impedance_matching

http://en.wikipedia.org/wiki/Complex_number

http://en.wikipedia.org/wiki/Electrical_length_(antenna)

http://en.wikipedia.org/wiki/Transformer

http://en.wikipedia.org/wiki/Antenna_tuner

http://en.wikipedia.org/wiki/Balun

http://en.wikipedia.org/wiki/Inductor

http://en.wikipedia.org/wiki/Capacitor

http://en.wikipedia.org/wiki/Antenna_effective_area

http://en.wikipedia.org/wiki/Radio_frequency

http://en.wikipedia.org/wiki/Root_mean_square

http://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)

http://en.wikipedia.org/wiki/Copper_loss

http://en.wikipedia.org/wiki/Antenna_efficiency




For an antenna with an efficiency of less than 100%, both the effective area and gain

are reduced by that same amount. Therefore the above relationship between gain and

effective area still holds. These are thus two different ways of expressing the same

quantity. Aeff is especially convenient when computing the power that would be

received by an antenna of a specified gain, as illustrated by the above example.

Antenna temperature:-

If we replace a resistor by a lossless antenna of radiation resistance R in an any

anechoic chamber at temperature Tc, then under condition Tr =Tc, the noise power

per unit bandwidth remains same. Finally if we remove antenna form anechoic

chamber and kept pointing to the sky at temperature Ts then the noise power per unit

bandwidth remains unchanged if the temperature Ts and Tr are same. This condition

is studied under the assumption that the whole radiation pattern is at sky temperature

Ts. In this way, antenna can be used to measure distinct temperature and it is called

passive remote sensing. The antenna used for remote sensing is called radio telescope.

To measure the distant temperature, the antenna noise temperature is compared with

that of resistor at temperature Tr. For comparison of the two temperatures, the

antenna is connected to the receiver and then the resistor is connected to the receiver.

When there is no difference in the temperature, we get condition Ta=Ts=Tr. Thus the

noise temperature Ta of a losses antenna is equal to the sky temperature Ts and not

equal to the physical temperature. But this is contradictory to the resistor because it is

loss and hence its noise temperature is equal to the physical temperature. Hence for a

practical antenna used for the remote sensing, the noise power per unit bandwidth is

given by,

P=kTa w/Hz.

Antenna polarization:-

The polarization of an antenna is the orientation of the electric field (E-plane) of the

radio wave with respect to the Earth's surface and is determined by the physical

structure of the antenna and by its orientation. It has nothing in common with antenna


http://en.wikipedia.org/wiki/Polarization_(waves)

http://en.wikipedia.org/wiki/E-plane



directionality terms: "horizontal", "vertical", and "circular". Thus, a simple straight

wire antenna will have one polarization when mounted vertically, and a different

polarization when mounted horizontally. "Electromagnetic wave polarization

filters" are structures which can be employed to act directly on the electromagnetic

wave to filter out wave energy of an undesired polarization and to pass wave energy

of a desired polarization. Reflections generally affect polarization. For radio waves

the most important reflector is the ionosphere - signals which reflect from it will have

their polarization changed unpredictably. For signals which are reflected by the

ionosphere, polarization cannot be relied upon. For line-of-sight communications for

which polarization can be relied upon, it can make a large difference in signal quality

to have the transmitter and receiver using the same polarization; many tens of dB

differences are commonly seen and this is more than enough to make the difference

between reasonable communication and a broken link. Polarization is largely

predictable from antenna construction but, especially in directional antennas, the

polarization of side lobes can be quite different from that of the main propagation

lobe. For radio antennas, polarization corresponds to the orientation of the radiating

element in an antenna. A vertical omnidirectional Wi-Fi antenna will have vertical

polarization (the most common type). An exception is a class of elongated waveguide

antennas in which vertically placed antennas are horizontally polarized. Many

commercial antennas are marked as to the polarization of their emitted signals.

Polarization is the sum of the E-plane orientations over time projected onto an

imaginary plane perpendicular to the direction of motion of the radio wave. In the

most general case, polarization iselliptical, meaning that the polarization of the radio

waves varies over time. Two special cases are linear polarization (the ellipse

collapses into a line) and circular polarization (in which the two axes of the ellipse are

equal). In linear polarization the antenna compels the electric field of the emitted

radio wave to a particular orientation. Depending on the orientation of the antenna

mounting, the usual linear cases are horizontal and vertical polarization. In circular

polarization, the antenna continuously varies the electric field of the radio wave

through all possible values of its orientation with regard to the Earth's surface.

Circular polarizations, like elliptical ones, are classified as right-hand polarized or

http://en.wikipedia.org/wiki/Ionosphere

http://en.wikipedia.org/wiki/Line-of-sight_propagation

http://en.wikipedia.org/wiki/Omnidirectional_antenna

http://en.wikipedia.org/wiki/WiFi

http://en.wikipedia.org/wiki/Ellipse

http://en.wikipedia.org/wiki/Linear_polarization

http://en.wikipedia.org/wiki/Circular_polarization



left-hand polarized using a "thumb in the direction of the propagation" rule. Optical

researchers use the same rule of thumb, but pointing it in the direction of the emitter,

not in the direction of propagation, and so are opposite to radio engineers' use.

2.3 Application of antenna:-

Military applications:-The high velocity aircrafts, space craft, missiles, rockets

require low profile, light weight antennas which can be conformably mounted to the

exterior surfaces of these vehicles. The micro strip antennas are best suited for above

application. Other areas where the micro strip antennas are used include application

areas such as missile guiding fusing telemetry, satellite communications radars,

altimeters, GPS etc.

Space applications:- The micro strip antennas are invariable used in the space

programs such as earth limb measurement Satellite, International sun earth explorer,

Shuttle Imaging radar, solar Mesospheric Explorer, Cosmic Background Explorer,

GEOSTAR, SEASAT and Mars Pathfinder. Out of these space program, the antennas

used for SEASAT and SIR-A, B, C series are all large panels consisting micro strip

arrays nearly 10m in length at L and C band frequencies. These arrays are apart

synthetic aperture radar used to perform earth remote sensing function.

Commercial applications:- The micro strip antenna are used commercially in

applications such as mobile Satellite communication, Direct Broadcast Satellite

services, Global positioning system, Aeronautical and Marine Radar and Earth

Remote sensing.



CHAPTER: 3

METHODOLOGY ADOPTED



3. Methodology Adopted:-

Transmission Lines

Antenna Working

Antenna Tuning

Antenna Matching

Reflector structure

Mount structure

Drive mechanism

Fixing the feed onto the antenna

Description of Transmitter

Driver

Power amplification

3.1 Transmission Lines:-

A transmission line is any medium whereby contained RF energy is transferred from

one place to another. Many times a transmission line is referred to as “a length of

shielded wire” or a “piece of coax”. While technically correct, such casual references

often indicate a lack of understanding and respect for the complex interaction of

resistance, capacitance, and inductance that is present in a transmission line.

The diameter and spacing of the conductors as well as the dielectric constant of the

materials surrounding and separating the conductors plays a critical role in

determining the transmission line’s properties. One of the most important of these

properties is called characteristic impedance. Characteristic impedance is the value in

ohms at which the voltage-to-current ratio is constant along the transmission line. All

Links modules are intended to be utilized with transmission lines having a

characteristic impedance of 50 ohms.



In order to achieve the maximum transfer of RF energy from the transmission line

into the antenna, the characteristic impedance of the line and the antenna at frequency

should be as close as possible. When this is the case the transmission line and antenna

are said to be matched. When a transmission line is terminated into an antenna that

differs from its characteristic impedance, a mismatch will exist. This means that all of

the RF energy is not transferred from the transmission line into the antenna. The

energy that cannot be transferred into the antenna is reflected back on the

transmission line. Since this energy is not reflected into space, it represents a loss.

The ratio between the forward wave and the reflected wave is known as the Standing

Wave Ratio (SWR). The ratio between the sum of the forward voltage and the

reflected voltage is commonly called the Voltage Standing Wave Ratio (VSWR).

3.2 Antenna Working:-

The electric and magnetic fields radiated from an antenna form an electromagnetic

field. This field is responsible for the propagation and reception of RF energy. To

understand an antenna’s function properly, an in-depth review of voltage, current, and

magnetic theory would be required. Since this is not in keeping with the basic nature

of this application note, a simplistic overview will have to suffice. Assume for a

moment that a coaxial transmission line was stripped and the shield and center

conductor were bent at right angles to the line as illustrated. Presto, a basic antenna

called a half-wave dipole has just been formed.

3.3 Antenna Tuning:-

This is the process whereby the resonant point of an antenna is adjusted. In most

instances, this is accomplished by physically adjusting the antenna length. While

simple range tests can be used to blindly tune an antenna, a network analyzer is a

virtual necessity for serious characterization. In some cases external inductive or

capacitive components may be used to match and bring the antenna to resonance.

Such components can introduce loss. It should be



remembered that match and resonance do not necessarily translate into effective

propagation.

3.4 Antenna Matching:-

Antenna resonance should not be confused with antenna impedance. The difference

between resonance and impedance is most easily

understood by considering the value of VSWR at its lowest point. The lowest point of

VSWR indicates the antenna is resonant, but the value of that low point is determined

by the quality of the match between the antenna and the transmission line it is

attached to. This point of attachment is called the feed point. The point of resonance

is largely determined by antenna length, but how is antenna impedance determined.

When an antenna is at resonance it presents a purely resistive load. This resistance is

made up of three factors. First, when considered only as a conductor, there is loss

through the real physical resistance of the antenna element. This is

Called ohmic resistance loss. The second and most important area of loss is through

radiation resistance (Rr). Since the real and leakage resistances are usually negligible,

we will focus on radiation resistance. As mentioned previously, radiation resistance is

a hypothetical concept that describes a fictional resistance that, if substituted in place

of the antenna, would dissipate the same power that the antenna radiates into free

space. The radiation resistance of an antenna varies along the length of the antenna

element but our concern is with the resistance at the feed point. The radiation

resistance increases as a conductor lengthens. In general, the radiation resistance for a

¼-wave vertical is about 37-ohms, for a ½-wave about 73-ohms.

3.5 Reflector structure:-

The 6.3 m diameter antenna is made up of 4 quarter segment. Each and every quarter

is made up of 10 segments fixed on five trusses. Panels which are fixed to the trusses

are made up of fine aluminum expanded mesh strengthened with the help of channel

sections and tee sections whose end share fixed to the backup structure. Trusses are

composed of aluminum square tubes and the welded back up made up of hub and 20



trusses. The hubs and trusses are constructed in such a way that they constitute to the

high level of surface accuracy.

3.6 Mount structure:-

A simple tubular steel space frame makes up most of the mount structure. It allows

rotation about x-axis as well as y axis. The x axis drive rod is connected between the

top of the mounted structure and the concrete foundation. The y axis drive rod is

connected between the base of the x axis bearing mount and the reflector back up

structure on the left hand side as viewed from the rear of the antenna. The mount is

rigidly attached to the concrete base which is facing north such that it can survive

even in wind speeds up to 200 kmph.

3.7 Drive mechanism:-

It has a telescopic pipe arrangement and a screw rod within it along with drive

mechanism. It has a telescopic pipe arrangement and a screw rod within it along with

manual handle. There are mechanical angle indicators along the screw rod which

indicate the exact position and angle of the antenna with respect to both the axes.

3.8 Material:-

Most of the parts of the panel and antenna structure are made up of aluminum alloy

which has corrosion resistance and yield strength.

Fig. 2 Materials



3.9 Finish:-

The reflector is treated in the following order before installation (A) Etch primer is

applied after caustic soda acid treatment (b) Painted with white matt paint. The mount

is treated with the following (a) A hot dip which galvanizes all steel parts (b) Etch

primer treatment (c) White enamel paint is applied as a last coating

3.10 Fixing the feed onto the antenna:-

The feed is supported by a set of four pipes called as a quadruped. It is fixed before

the whole antenna structure is hoisted, that is, it is fixed on the ground itself before

the whole antenna structure is fixed. Care should be taken that the feed is at the exact

focus of the reflector. A maximum tolerance of +3mm is allowed for the separation

between the actual focus and feed position. Also the feed entrances and cable output

ports are water proof Teflon sheet to prevent the entry of moisture into the

arrangement. The LNBC (Low Noise Block Converter) and cables are connected to

the feed output. The x-y adjustment is then done and fixed. The bolts are tightened

with care and the arrangement is set. Care should be taken while lifting and fixing of

the whole apparatus to prevent any damage. The Trivandrum station has the

following specifications which are used for following advantages like the

maintenance personnel of one type can work with the other type as well and spare

parts can be shared. All amplifiers are WB devices (170 to 230 MHz in B3 and 44

and 88 MHz in B1) and can operate in band 3 and band 1 of both sound and vision. In

the driver Audio and video I/P signals are connected to vision and sound IF signals.

These IF proceed prior to concession to RF output frequencies and amplified. The

attenuated 5 and 10 KW sideband pattern is obtained through the use of a lithium

neonate ground wave filter. Each amplifier is equipped with AGC. The driver also

consists of a vision synchronization detection circuit used to automatically switch the

transmitter on and off. Also the transmitter can be controlled locally and remotely.

All IF and RF interconnections use 50ohmcoaxial links to simplify maintenance. By

the use of redundant of the ampliform and power supplies, briefly can estimated



reduced power levels in the event of a failure in several transistors amplifiers or a

power supply.

3.11 Description of Transmitter:-

The TX is in a single cabinet which the diplexer and filter assembly is associated. The

TX as discussed above has two drivers’ two RF amplification channels, power

supplies and associated co-ordination and control system, a diplexer and a RF filter.

All amps power supplies and their driver components are plug-in drawers and sub

assemblies are designed for easy access and removal. The main switch is designed for

use with all types of 3phiW/W with or without neutral 208V or 480V.

3.12 Driver:-

This subassembly is used to generate vision and sound signals corresponding to the

selected standard using input video and audio signals. This subassembly performs the

processing and conversion required to generate the filtered and vision and sound

signals in the selected RF band. The dent also provides phase and amplitude

corrections to ensure that the linearity specifications comply with various standards.

The driver acknowledges s the presence or absence of the video and audio signals that

are applied to the driver. The driver consists of plug-in mounted in a single PCB rack,

6 units high. Each driver has 5 modules connected to the mother board. Each can be

replaced separately without changing the entire assembly. Max Output power is

19ddBm for vision signals and 13dBm for sound signals. Local driver controls are on

the local freq and interface board. In the maintenance mode of the TX these controls

are active. The 2 drivers and associated passive resonance relays are directly

controlled by the control system. (Each driver has +_ 12V power supply).Each driver

has its own internal oscillator. However they can be made to work with an external

frequency synthesizer. In case of synthesizer failure the change into internal oscillator

takes place automatically. In this dual drive configuration the sys automatically

switches over to the reserve driver.



3.13 Power amplification:-

The driver generates a low power vision RF signal and a low power sound RF signal.

They are applied to the vision and sound amplification chains consisting of identical

parallel wired high gain amplifier decreases.

Fig. 3 Power Amplification

These drivers are used for the 10Kw sys. They are distributed as follows each high

gain amplifier provides a power of 1600 W at peak .Three 2X300 W amplifiers

grouped by a empty system diagonal power in the high generator amplifier drawer

to1600W peak .A power supply distribution board. Each amplifier has its own

protection devices for

1. Power surge

2. SWR

3. Temperature rise the LCD screen provides control system monitoring and analysis.



The amplifier drivers are provided by plug in high power supplies. (1 power supply

for 2 amplifiers.) These highly reliable units generate 50V with 120. The dish antenna

does one amplification by concentrating the signals at the focus. The LNB mounted

exactly at the focus amplifies this signal again. This signal cannot be sent through a

coaxial cable because of high frequency attenuation. So the LNB converts it to a

lower frequency between .950MHzto2.150MHz as that is the frequency required by

the IRD. The IRD used is a Scopus IRD. it has a demultiplexer, an MPEG-2 video

and audio decoder as well as data and VBI insertion functions. It can also handle high

seed and low speed data input functions. And has an on board DVB descrambling

with BISS mode1 and BISS-E support. It can be used to descramble Scopus CAS

5000 encryption system and a DSNG CA fixed key encryption system.



CHAPTER: 4

EXPECTED OUTCOME OF

INDUSTRIAL TRAINING



4. Expected Outcome of Industrial Training:-

4.1. Advantages:-

The most widely used antenna is parabolic reflector antenna. It provides following

advantages:

Increased overall gain.

It provides diversity reception.

It cancels out interference from a particular set of directions.

It steer the array so that it is most sensitive in a particular direction.

It determines the direction of arrival of the incoming signals.

To maximize the Signal to Interference plus Noise Ratio (SINR).

Low cross polarization.

Wide bandwidth.

Narrow beam width pattern

4.2 Disadvantages:-

Because of large size antenna, it can’t be used at low frequencies.

Main beam is pencil shaped and is surrounded by number of side lobes producing

electromagnetic interference.

At the edges of parabolic diffraction takes place resulting in side lobes. It

produces electromagnetic induction.

The feed antenna can’t be located at the focus exactly.

The parabolic is not illuminated uniformly and tapers at the edges leading to the

smaller capture area.



5. CONCLUSION

I had a very knowledgeable experience during my industrial training. I have learnt

about different equipment like TV Transmitter, Studio equipment’s, Earth Station and

their associated equipment. There I studied about antenna, structure of antenna, their

radiation patterns, its characteristics, the advantages and disadvantages of many

instruments used for transmitting and receiving audio and video signals, way the

audio and video signals are transmitted over a distance of hundreds of thousands of

kilometers, how the noise interfere the signals and how it can be avoided. I learnt

about antenna working, antenna tuning, antenna matching, feed of antenna, antenna

used in transmitter and receiver, specific antennas used in Doordarshan-I and

Doordarshan-II, number of channels broadcasted by Doordarshan Kendra, Indore. I

came to know about the technique of displaying programs on the television. I had a

practical experience of how the artistes record their shows, type and numbers of

cameras used in studio, the audio and video signals are then synchronized, modulated

and finally telecasted to the house of thousands of people.



6. Reference

1.en.wikipedia.org/wiki/Doordarshan

2. www.ddindia.gov.in/

3. Antenna and Wave Propagation by K.D. Prasad, Deepak Handa

http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22K.D.+Prasad%22

http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22Deepak+Handa%22

ANTENNA AND ITS FUNDAMENTAL REPORT

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