Basics of _antennas (1)

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Basic Antenna Theory &Communications Antenna

System

ComeC 513 2013



Agenda

Antenna definition

Antenna theory

Antenna parameters Types of Antenna

Applications







Antenna

An antenna is a circuit element that provides a transition from aguided wave on a transmission line to a free space wave and itprovides for the collection of electromagnetic energy.



Antenna Definition-cont‟d

In transmit systems the RF signal is generated,

amplified, modulated and applied to the

antenna

In receive systems the antenna collectselectromagnetic waves that are “cutting”

through the antenna and induce alternating

currents that are used by the receiver



Antenna Types

High Frequency1.6 - 30 Mhz + 50 Mhz

160 - 6 meters

An antenna‟s size/length depends on the

frequency

It‟s functionality largely depends on the

height above ground, as well as the polarity

and it‟s configuration



Antennas A good antenna works A bad antenna is a waste of time & money

Antenna systems can be very inexpensive and simple

They can also be very, very expensive

Antenna Considerations –The space available for an antenna

–The proximity to neighbors

–The operating frequencies you will use

–The output power

–Money



Isotropic Antenna

The isotropic antenna is a hypothetical point source.

It does not exist in reality but is considered as an

important starting point considering different antennas

from the theoretical to the practical

The pattern is a Cardioid - a donut shape or a sphere



Current and voltage distribution on an antenna.

1. A current flows in theantenna with an amplitude

that varies with the generator

voltage.

1. A sinusoidal distribution of charge exists on the

antenna. Every 1/2 cycle, the

charges reverse polarity.

2. The sinusoidal variation in

charge magnitude lags the

sinusoidal variation in current

by 1/4 cycle.



Standing wavesof voltage and

current on an

antenna.



Reciprocity

An antenna ability to transfer energy form the

atmosphere to its receiver with the same

efficiency with which it transfers energy from the

transmitter into the atmosphere.

Antenna characteristics are essentially the

same regardless of whether an antenna is

sending or receiving electromagnetic energy



Reciprocity

RECIPROCITY of

antennas means that

the various propertiesof the antenna apply

equally to transmitting

and receiving



Polarization

Polarization is the direction of the electric fieldand is the same as the physical attitude of the

antenna

A vertical antenna will transmit a vertically

polarized wave

The receive and transmit antennas need to

possess the same polarization



Antenna Polarization

- Vertical or horizontal

Vertical waves travel @ 90 to the earths surface

Horizontal waves travel parallel to the earth‟s surface

Usually wire antennas are horizontal but an inverted„V‟ dipole has a vertical component

Yagi type antennas can be either vertical or horizontal

Circular antennas can be both vertical and horizontal Usually, horizontally polarized antennas receives less

noise



Terms And Definitions

RADIATION RESISTANCE is the amount of

resistance which, if inserted in place of the

antenna, would consume the same amount of

power that is actually radiated by the antenna.

RADIATION PATTERNS can be plotted on a

rectangular- or polar-coordinate graph. These

patterns are a measurement of the energy

leaving an antenna.



Dipole antenna



EEE381B

Dipole Antenna

Characteristics

Polarization: vertical

Beamwidth: 80° x 360°

Bandwidth: 10%

Gain: 2 dB

Typical Applications

TV “Rabbit ears”

FM radio (folded dipole)

Radio mast transmitters



EEE381B

Simplified Radiation PatternsElevation,El

Azimuth, Az



3-D pattern

• Antenna radiation pattern is 3-

dimensional

The 3-D plot of antenna patternassumes both angles θ and ϕ varying,

which is difficult to produce and to

interpret 3-D pattern

Source: NK Nikolova



Reference antenna (λ/2 dipole)

• Isotropic antenna or isotropic radiator is a hypothetical (not

physically realizable) concept, used as a useful reference to describe

real antennas.

Isotropic antenna radiates equally in all directions. Its radiation

pattern is represented by a sphere whose center coincides with the

location of the isotropic radiator.

Source: NK Nikolova



Generally speaking, there are two „types‟ of antenna:

1. Direc tio nal

- this type of antenna has a narrow beamwidth; with

the power being more directional, greater distances

are usually achieved but area coverage is sacrificed

- Yagi, Panel, Sector and Parabolic antennae

2. Omn i -Direc tional

- this type of antenna has a wide beamwidth and

radiates 3600

; with the power being more spread out,shorter distances are achieved but greater coverage

attained

- Omni antenna



Omni- typical gains of 3 to 10 dBi



Radiation Pattern

Radiation pattern is an indication of radiated fieldstrength around the antenna.

Power radiated from a /2 dipole occurs at right

angles to the antenna with no power emitting

from the ends of the antenna.

Optimum signal strength occurs at right angles or 180° from opposite the antenna



Radiation Patterns

Radiation pattern

Graphical representation of radiation properties of

an antenna

Depicted as two-dimensional cross section

Beamwidth (or half-power beam width)

Measure of directivity of antenna

Reception pattern

Receiving antenna‟s equivalent to radiation pattern



Radiation Pattern for Vertical Antennas

antenna

/4

/2



Antenna Radiation Patterns

Common parameters

– main lobe (boresight)

– half-power beamwidth (HPBW)

– front-back ratio (F/B)

– pattern nulls

Typically measured in two planes:

• Vector electric field referred to E-field

• Vector magnetic field referred to H-field



Typical Radiation Pattern for an Omni



A LOBE is the area

of a radiation pattern

that is covered by

radiation.

A NULL is the area of a radiation pattern

that has minimum

radiation.



Beamwidth

Beamwidth is the angular separation

of the half-power points of theradiated pattern



beamwidth

antenna

• A

Power 3dB down

from maximum

point A

Max power

2 dipole

Directional Antenna

Radiated energy is

focused in a specific

direction



TYPES OF ANTENNAS

Isotropic antenna (idealized) Radiates power equally in all

directions

Dipole antennas

Half-wave dipole antenna (or

Hertz antenna)

Quarter-wave vertical antenna

(or Marconi antenna)

Parabolic Reflective Antenna



Antenna

HERTZ (half-wave) and MARCONI (quarter-

wave) are the two basic classifications of

antennas.



HERTS ANTENNA OR HALFWAVE

DIPOLE -consists of two lengths of

rod or tubing, each a quarter-wave

long at a certain frequency, whichradiates a doughnut pattern.

physical length - one-half wavelength

of the applied frequency

called a Hertz antenna or a half-wave

dipole antenna.

Hertz antennas are not found at

frequencies below 2MHz because of

the physical size needed of theantenna to represent a half-wave.



A QUARTER-WAVE

ANTENNA (Marconi) is a ¼

antennna (total of half-wave

antenna) cut in half with oneend grounded.

Also called Vertical Antennas

are used for frequencies under

2 MHz. It uses a conducting path to

ground that acts as ¼

wavelength portion the antenna

above the ground. The above ground structure

represents a /4 wavelength



Types of Antennas

Simple wire

– Dipole – Folded dipole

– Trap dipole

– Offset or Windom antenna – Phased dipoles

– Vertical or horizontal (both)

– Beverage wave antenna



Types of Antennas

–Metal

–Vertical

–Yagi

–Trap Yagi

–Phased arrays –Loops

–Vertical or Horizontal

–Horns for super ultra high frequencies –Mobile antennas



Horizontal and Dipole Antennas

38

A “horizontal antenna” is an antenna that is a simple dipolemounted so the elements are parallel to the earth's surface.

So what’s a dipole?

A dipole antenna consists of two sections that areeach approximately one-quarter of the wavelengthof that band, so that the total length is equal toabout one-half wavelength. It is a simple antennadesigned to work best on a single band.

The transmission line from the radio is connectedto this antenna in the middle of the two sections.



Dipole Antenna

39

This is an example of a dipole antenna. Many hams getting on HF for the first time often start with a dipole. If you have the room for one, thedipole is cheap and easy to build.



Dipole Antenna



Vertical Antennas A “Vertical Antenna”- is an antenna that consists of a

single element mounted perpendicular to the earth's

surface.

Most mobile antennas are verticals.

Verticals usually require some sort of counterpoise towork their best. In a fixed station, a vertical may either bemounted on the ground or on a mast, and it may alsohave several radials for counterpoise.

These radials may be laid out on the ground, as in thenext slide, or mounted just underneath the verticalelement, as in an elevated ground plane.

In a mobile installation, the metal body of the car usuallyserves as the counterpoise.



Vertical (Marconi) Antenna – cont‟d

Poor grounding conditions of the earth/soil

surrounding the antenna can result in serious

signal attenuation.

This problem is alleviated by installing a

counterpoise



Counterpoise

Counterpoise is a grounding grid established

where the earth grounding cannot satisfy

electrical requirements for circuit completion.

It is designed to be non-resonant at the

operating frequency



Counterpoise-cont‟d

supports

antenna

radius = ¼



Typical Ground-Mounted Vertical

45

This is a rough diagram of a ground-mounted vertical. Theorange radials you see may be laid along the top of the ground or buried just beneath the surface.



The GROUND SCREEN and the COUNTERPOISE are used to reducelosses caused by the ground in the immediate vicinity of the antenna.

The ground screen is buried below the surface of the earth. The

counterpoise is installed above the ground.



Ground Plane Antenna

47

Ground plane antenna – another type of verticalantenna. It is designed to be mounted on a mast,and usually has three or four radials coming fromthe base of the antenna.





EEE381B

Loop

El

Az

Characteristics

Polarization: horizontal Beamwidth: 80° x 360°

Bandwidth: 10%

Gain: -2 dB


AM Broadcasting



The FOLDED DIPOLE consists of a dipole

radiator, which is connected in parallel at its ends

to a half-wave radiator.

A LONG WIRE ANTENNA i t th t i



A LONG-WIRE ANTENNA is an antenna that is a

wavelength or more long at the operating

frequency.

These antennas have directive patterns that are

sharp in both the horizontal and vertical planes.



BEVERAGE ANTENNAS consist of a single wire

that is two or more wavelengths long.



A V ANTENNA is a bidirectional antenna consisting

of two horizontal, long wires arranged to form a V.



The RHOMBIC ANTENNA uses four conductors joined toform a rhombus shape. This antenna has a wide frequencyrange, is easy to construct and maintain, and is noncritical asfar as operation and adjustment are concerned.



Helical

El & Az

Characteristics

Polarization: circular (axial

mode) Beamwidth: 50° x 50°

Bandwidth: 70%

Gain: 10 dB


Mobile communications GPS

Space communication

Animal tracking



The TURNSTILE ANTENNA consists of two

horizontal, half-wire antennas mounted at right

angles to each other.





Antenna Array

Antenna array is a group of antennas or

antenna elements arranged to provide the

desired directional characteristics.

Generally any combination of elements can

form an array. However, equal elements in a

regular geometry are usually used.



AN ARRAY is a combination of half-wave elements operating together

as a single antenna. It provides more gain and greater directivity than

single element antennas.

A DRIVEN ARRAY derives its power directly from the source.

A PARASITIC ARRAY derives its power by coupling the energy from

other elements of the antenna.

The BIDIRECTIONAL ARRAY radiates energy equally in two opposingdirections.

The UNIDIRECTIONAL ARRAY radiates energy efficiently in a single

direction.

The COLLINEAR ARRAY has elements in a straight line. Maximum

radiation occurs at right angles to this line. The BROADSIDE ARRAY has elements parallel and in the same

plane. Maximum radiation develops in the plane at right angles to the

plane of the elements.



• The BROADSIDE ARRAY has elements parallel and in the sameplane. Maximum radiation develops in the plane at right angles to

the plane of the elements.



The END-FIRE ARRAY has elements parallel to each other and in thesame plane. Maximum radiation occurs along the axis of the array.



Phased Array

El

Az

Characteristics

Polarization: linear / circular Beamwidth: 0.5° x 30°

Bandwidth: varies

Gain: 10 to 40 dB


Radio broadcasting Search & track radar

Weather radar

(severe storm watch)



Military Phased Array Usage



Phased array antennas

Phased array antennas have become anextremely important type of radar for militaryuse, particularly airborne use.

In radar applications, phased arrays permit

near instant switching from one target toanother, and from search to track mode.

Phased arrays combined with “smart skin”technology have radically altered airborne

avionics designs.



EEE381B

Basic phased array architecture

Signal Divider / Combiner

Phase

Shifter

Phase

Shifter

Phase

Shifter

Phase

Shifter

Phase

Shifter

Phase

Shifter

Steering angle, s

Element spacing









Pointers in antenna design:

MATCHING STUBS are used between elements to maintain

current in the proper phase.

The GAIN OF A COLLINEAR ANTENNA is greatest when the

elements are spaced from 0.4 to 0.5 wavelength apart or when

the number of elements is increased.

The OPTIMUM GAIN OF A BROADSIDE ARRAY is obtained

when the elements are spaced 0.65 wavelength apart.

A PARASITIC ARRAY consists of one or more parasiticelements with a driven element. The amount of power gain and

directivity depends on the lengths of the parasitic elements andthe spacing between them.



ARRAYS, such as the YAGI, have a narrow Frequency

response as well as a narrow beamwidth.





Yagi-Uda Antenna-cont‟d

reflector

dipole

antenna

/4

Radiated Directed Signal



antenna

2 dipole radiated signal

without reflector

2 dipole radiated signal

with reflector

Radiated Directed Signal



The Antenna Formula

c

f = frequency of the signal

c = is the speed of light = 186,000 mi/sec

= is the wavelength of the signal, use 3 x 108

when dealing in meters for the speed of light



The Antenna Formula - applied

If a half-wave dipole antenna needed to beconstructed for a 60 Hz signal, how large

would it need to be?

c 186,000 mi sec

60= 3100 mi

2 = 1550 miles!



Radiation & Induction Fields

The mechanics launching radio frequencies

from an antenna are not fully understood.

The RF fields that are created around theantenna have specific properties that affect

the signals transmission.

The radiated field is known as the radiation

field

R di ti & I d ti Fi ld t‟d



Radiation & Induction Fields-cont‟d

There are two induction fields or areas wheresignals collapse and radiate from the antenna.

They are known as the near field and far

field .

The distance that antenna inductance has onthe transmitted signal is directly proportional

to antenna height and the dimensions of the

wave.

R 2D2



Radiation & Induction Fields-cont‟d

R 2D2

Where: R = the distance from the antenna

D = dimension of the antenna

= wavelength of the transmitted signal



Radiation Resistance

Radiation Resistance is the portion of the antenna’s

impedance that results in power radiated into space

(i.e., the effective resistance that is related to the power

radiated by the antenna.

Radiation resistance varies with antenna length.

Resistance increases as the increases



Antenna Impedance

A proper Impedance Match is essential for maximumpower transfer. The antenna must also function as a

matching load for the Transmitter ( 50 ohms).

Voltage Standing Wave Ratio (VSWR), is an indicator of how well an antenna matches the transmission line

that feeds it. It is the ratio of the forward voltage to the

reflected voltage.

The better the match, the lower the VSWR. A value of

1.5:1 over the frequency band of interest is a practical

maximum limit.



• Return Loss is related to VSWR, and is a measure of

the signal power reflected by the antenna relative to

the forward power delivered to the antenna.

• The higher the value (usually expressed in dB), the

better.

• A figure of 13.9dB is equivalent to a VSWR of 1.5:1.

• A Return Loss of 20dB is considered quite good, and is

equivalent to a VSWR of 1.2:1.



VSWR Return Loss Transmission Loss

1.0:1 0.0 dB

1.2:1 20.83 dB 0.036 dB

1.5:1 13.98 dB 0.177 dB

5.5:1 3.19 dB 2.834 dB

P i t S R di t



Point-Source Radiator

Consider a source of electro-magnetic radiation that

radiates in all directions equally.

Such a source is called isotropic.

Let the total power radiated by the source be P T .

Let the source be surrounded by a sphere or radius d . If there are no objects inside the sphere to absorb or

reflect the radiation, all of the power from the source

will hit or cross the sphere.

The surface area of a sphere is 4πd 2

.



Antenna Gain



Antenna Gain

• The antenna power gain is defined as

• Since an antenna is a passive device, it has the same gain whether it is transmitting or receiving.

Effective Isotropic Radiated Power



Effective Isotropic Radiated Power

The Effective Isotropic Radiated Power (EIRP) of

an antenna is power input required of an isotropicantenna to produce the same power density on thebore sight as the actual antenna.

P ERIP = P T GT

Power Density at d = (P ERIP )/ (4π d 2 )= (P T GT )/(4π d 2 ) (w/m2 )

d = distance from the antenna

The EIRP is the transmitted power multiplied by thegain of the transmitting antenna.

Eff ti R di t d P (ERP)



Effective Radiated Power (ERP)

ERP = the power input value multiplied by the

gain of the antenna

dBi = isotropic radiator gain dBd = dipole antenna gain

Effective Area



If the receiving antenna is placed d meters fromthe transmitting antenna, it will act like a catcher‟s

mitt and intercept the power in an effective area

of Ae (m2).

watt





Effective area - Related to physical size and shape of

antenna





Antenna Gain

Antenna gain is the measure in dB

how much more power an antenna

will radiate in a certain direction withrespect to that which would be

radiated by a reference antenna

Antenna Gain



Directive Gain – ratio of the power density in a particulardirection of one antenna to the power density that would

be radiated by an omnidirectional antenna (isotropicantenna).

Directivity – refers to the ability of an antenna to send

and/or receive signals over a narrow horizontal directionalrange.

Gain of Hertzian Dipole with respect to an isotropicantenna = 1.5:1 or 10 log 1.5 = 1.76 dB gain over

isotropic source.

The gain of a half-wave dipole compared to the isotropicantenna = 1.64:1 or 10 log 1.64 = 2.15 dB.



Antennas – Gain



Gain

, ,G eD

The power gain, G, of an antenna is very much like itsdirective gain, but also takes into account efficiency

The maximum power gain

max maxG eD

The maximum power gain is often expressed in dB.

max max1010logG GdB



Antenna Height

Antenna height above the ground is directly related toradiation resistance. Ground reflections causing out-of-phase signals to be radiated to receiving antennas

will degrade the transmission.

Physical length and electrical length of most antennasare approximately 95% of the physical length. Ideal

antenna height is usually based on trial and error procedures

Di l L th



Dipole Length:

Antenna is a frequency sensitive device.

λ = c/f λ = 984/f (MHz); λ/2 = 492/f (MHz) (feet)

Example:

f = 122 MHzλ/2 = 492/f (MHz) = 492/122 = 4.033 feet.

End Effect:λ/2 = 492/f (MHz) x 0.95 = 468/f(MHz)

If f= 27 MHz. L = 468/27 = 17.333 feet,therefore λ/4 = 8.66 feet.

Antenna Q and Bandwidth:



Bandwidth is determined by the frequency of operation while “Q” is thequality of the antenna circuit.

BW = f/Q

If Q is high bandwidth is narrow, if Q is low, BW is wider.For resonant circuit Q>10, which makes the circuit more selective.

SWR below 2:1 – good design

Q and BW- are determined primarily by the ratio of the length to thediameter of the conductor. Also affected by the number of conductorsused and their spacing to the dipole.

Q= XL / R BW = F/Q

Note: Lowering Q increases the BW; lower Xl reduces Q and increases BW. UHF

antenna- short and fat conductors are used to improve Q and BW.



λ = c/f c= velocity of EMW

L = c/f x 0.95 Vf= 0.95 c (end effect)

L = (3x 108 / 5 X 105)X 0.95 = 570 meters

or 2244 feet

Problem:

Determine the length of an antenna operating atfrequency 500 KHz.



Directivity and Power Gain



Directivity and Power Gain

Power Gain – comparison of the output power of anantenna in a certain direction to that of an isotropicantenna.

Antenna Gain – is the power ratio comparison between

an omnidirectional and unidirectional radiator.

A(dB) = 10 log (P2 /P1)

Where: P1 = power of unidirectional antennaP2 = power of the reference antenna



A (dB) = 10 log (P2 /P1)

2.15 dB = 10 log (P2 /1000)

P2 /1000 = log -1 (2.15/10)

P2 = 1.64 x 1000 = 1640 watts

Problem:

A half-wave dipole antenna is capable of radiating 1-kWand has a 2.15 dB gain over an isotropic antenna. Howmuch power will be delivered to the isotropic(omnidirectional) antenna, to match the filed strength of a directional antenna?

ERP (Effective Radiated Power) - field gain of the



gantenna and the efficiency of the transmitter.

ERP = Po x (Field Gain)2

Example:

If an antenna has a field gain of 2 and the transmitter

has an overall efficiency of 50% (circuit and x’missionline losses) then, if a 1-kW signal is fed to the finals,this will results in 500 w being fed to the antenna.What is the ERP?

ERP = Po x (Field Gain)2 = 500 x 2 2 = 2000 w

Radiation and Field Intensity



Radiation and Field Intensity

Field Intensity – the field of an antenna’s radiation at agiven point in space, is equal to the amount of voltageinduced in a wire antenna 1 meter long, located a thatgiven point.

Factors affecting FI: time, atmospheric condition anddistance.

Antenna Resistance – hypothetical value which, if replaced

by an equivalent resistor, would dissipate exactly the sameamount of power that the antenna would radiate. This isthe ration of the power radiated by the antenna to thesquare of the current at the feed point.

Antenna Losses and Efficiency



Antenna Losses – due to the ground resistance, corona effects,imperfect dielectric near the antenna, energy loss due to eddy current

induced into nearby metallic objects, and I2R losses in the antennaitself.

P in = P d + P rad

P in – power delivered to the feed point

P d – power lostP rad – power actually radiated

I 2 R in = I 2 R d + I 2 R rad

R in = R d + R rad

Antenna Efficiency = η = (R rad / (R d + R rad )

Low and medium frequency antenna approximately 75 to 95 %efficiency. HF antenna have approximately 100% efficency.

Antennas – Efficiency



Power is fed to an antenna through a T-Line and

the antenna appears as a complex impedance

Efficiency

.ant ant ant

Z R jX

ant rad dis R R R

where the antenna resistance consists of radiation resistance and and a dissipativeresistance.

21

2

rad o rad P I R

21

2

diss o diss P I R

The power dissipated by ohmic losses isThe power radiated by the antenna is

An Antenna Efficiency “e” can be defined as the ratio of the radiatedpower to the total power fed to the antenna.

rad rad

rad diss rad diss

P Re

P P R R

For the antenna is driven by phasor current j

o s I I e



Polarization



An antennas polarization is relative to the E-field of antenna.

– If the E-field is horizontal, than the antenna is

Horizontally Polarized.

– If the E-field is vertical, than the antenna isVertically Polarized.

Polarization

No matter what polarity you choose, all antennas inthe same RF network must be polarized identically

regardless of the antenna type.

Polarization may deliberately be used to:



– Increase isolation from unwanted signal sources (Cross

Polarization Discrimination (x-pol) typically 25 dB)

– Reduce interference

– Help define a specific coverage area

Horizontal

Vertical







Beam Antennas - Quad



113

The quad, Yagi, and dish are all examples of beamantennas. A quad antenna looks something like a metalframe for a box kite. If you look closely, you can see theantenna wires supported by the “X” framework.

Quad antenna



Quad antenna

Beam Antennas Yagi



Beam Antennas - Yagi

115

The yagi is a one dimensional beam antenna

consisting of several elements. It may be mountedhorizontally, as shown here, or vertically.

Log Periodic

http://upload.wikimedia.org/wikipedia/commons/f/f7/Schwarzbeck_UHALP_9108_A.jpg



EEE381B

Log Periodic

El

Az

Characteristics

Polarization: vertical / horizontal


Bandwidth: 10 to 1

Gain: 6 to 8 dB


Amateur radio

Yagi



EEE381B

Yagi

El

Az

Characteristics

Polarization: horizontal


Bandwidth: 5%

Gain: 5 to 15 dB


WWII airborne radar Amateur radio



Yagi- better suited for shorter links

- lower dBi gain; usually between 7 and 15 dBi



Typical Radiation Pattern for a Yagi

LOG PERIODIC ANTENNA



LOG PERIODIC ANTENNA





Cavity Backed Spiral



EEE381B

y

El & Az

Characteristics

Polarization: circular


Bandwidth: 9 to 1

Gain: -15 to +3 dB


Radar altimeter

Electronic warfare

Conical Spiral



EEE381B

El & Az

Characteristics

Polarization: circular


Bandwidth: 4 to 1

Gain: 5 to 8 dB


Ground penetrating radar

Electronic warfare





Beam Antennas - Dish



Beam Antennas - Dish

127

Another beam antenna is the dish or parabolic

reflector. It is often used to receive UHF signals or TV signals beamed from satellites, such as DishNetwork ® antennas.

Parabolic



EEE381B

El & Az

Characteristics

Polarization: depends on feed

Beamwidth: 0.5° x 30°

Bandwidth: varies

Gain: 10 to 55 dB


Satellite TV

Cellular telephony, Wi-Fi

Radio astronomy

Search & track radar

PARABOLIC ANTENNA



PARABOLIC ANTENNAThe parabolic dish antenna -

consists of one circular parabolic reflector and a point

source situated in the focal

point of this reflector. This

point source is called „primary

feed” or „feed” .

The circular parabolic

(paraboloid) reflector is

constructed of metal, usually a

frame covered by metal mesh

at the inner side. The width of the slots of the metal mesh

has to be less than λ/10. This

metal covering forms the

reflector acting as a mirror for

the radar energy.

Parabolic



- used in medium to long links

- gains of 18 to 28 dBi- most common



Typical Radiation Pattern for a Parabolic

PARABOLIC ANTENNA

RADIATION PATTERN



RADIATION PATTERN

THE CASEGRAIN ANTENNA



In telecommunication and radar use, a Cassegrain antenna is an antenna inwhich the feed radiator is mounted at or near the surface of a concave main

reflector and is aimed at a convex subreflector. Both reflectors have a common

focal point. Energy from the feed unit (a feed horn mostly) illuminates the

secondary reflector, which reflects it back to the main reflector, which then forms

the desired forward beam.











QUESTIONS

Isotropic Source



Isotropic Source

1.What is an isotropic antenna? hypotheticalpoint source

2. Describe the antenna radiation pattern for anisotropic radiator? A sphere

3. What determines the polarization of an

antenna? the electric field4. What does horizontal wave polarization

mean? The electric lines of force of theradio wave is parallel to the earth's surface

5. What does vertical wave polarization mean?The electric lines of force of a radio waveare perpendicular to the earth's surface



Microwave Parameters:



2

DG

141

General Equation:

B. Parabolic Antenna Gain, G

where:D = antenna diameter in mλ = signal wavelength in m

η = efficiency




2

6

DG

142

Antenna Gain for Typical Values of η (0.55 to 0.75):

Parabolic Antenna Gain for Typical Values of η (0.55 to0.75) in Metric system:

)(10)(10

log20log204.42m MHz

D f G

)(10)(10 log20log208.17 mGH z D f G




143

Parabolic Antenna Gain for Typical Values of η (0.55 to 0.75) in English system:

)(10)(10 log20log206.52 ft MHz D f G

)(10)(10 log20log205.7 ft GHz D f G







S t l



Sectoral

- directional in

nature, but can be

adjusted anywhere

from 450 to 1800

- typical gains vary

from 10 to 19 dBi



GSM and CDMA cellsite

antenna

array for thecellular

telephone

system``

0

0



90

180

270 0 -3 -6 -10

-15

-20

-30

dB90

180

270 0 -3 -6 -10

-15

-20

-30

dB

Typical Radiation Pattern for a Sector

Beamforming Antenna



g



Smart Antennas



SMART ANTENNA



A smart antenna is a digital wireless communicationsantenna system that takes advantage of diversity effect atthe source (transmitter), the destination (receiver), orboth.

Diversity effect involves the transmission and/or receptionof multiple radio frequency (RF) waves to increase dataspeed and reduce the error rate.

SMART ANTENNA

Smart antennas fall into three major categories:



Smart antennas fall into three major categories:1.SIMO (single input, multiple output),

2.MISO (multiple input, single output), and3.MIMO (multiple input, multiple output).

• In SIMO technology, one antenna is used at the source,

and two or more antennas are used at the destination.• In MISO technology, two or more antennas are used atthe source, and one antenna is used at the destination.

• In MIMO technology, multiple antennas are employed atboth the source and the destination.

• MIMO has attracted the most attention recently becauseit can not only eliminate the adverse effects of multipathpropagation, but in some cases can turn it into anadvantage.

Smart Antennas Smart antennas (also known as adaptive



Smart antennas (also known as adaptive

array antennas, multiple antennas and,recently, MIMO)

are antenna arrays with smart signal

processing algorithms used to identify spatialsignal signature such as the direction of

arrival (DOA) of the signal, and use it to

calculate beamforming vectors, to track and

locate the antenna beam on the mobile/target.

The antenna could optionally be any sensor.

Smart Antennas



Smart Antennas are base station antennas with apattern that is not fixed, but adapts to the current

radio conditions

Smart Antennas have the possibility for a large

increase in capacity: an increase of three times

for TDMA systems and five times for CDMA

systems has been reported.

Major drawbacks and cost factors include

increased transceiver complexity and more

complex radio resource management

Smart Antennas



The idea of smart antennas is to use basestation antenna patterns that are not fixed, but

adapt to the current radio conditions.

This can be visualized as the antenna directing

a beam toward the communication partner only Smart antenna techniques are used notably

in acoustic signal processing, track and

scan RADAR, radio astronomy and radio

telescopes, and mostly in cellular systemslike W-CDMA and UMTS.

Smart Antennas



Smart antennas add a new way of separatingusers, namely by space, through SDMA

(space division multiple access)

By maximizing the antenna gain in the desired

direction and simultaneously placing minimal

radiation pattern in the directions of the

interferers, the quality of the communicationlink can be significantly improved

Smart Antenna





Elements of a Smart Antenna



Smart antennas consists of a number of radiating

elements, a combining/dividing network and a

control unit





Intelligent Antennas-



Dynamically phased array (PA):

By including a direction of arrival (DoA) algorithm

for the signal received from the user, continuoustracking can be achieved and it can be viewed as

a generalization of the switched lobe concept

Intelligent Antennas-



Adaptive array (AA): In this case, a DoA algorithm for determining the direction toward interference sources(e.g., other users) is added.

The radiation pattern can then be adjusted to null outthe interferers.

In addition, by using special algorithms and spacediversity techniques, the radiation pattern can beadapted to receive multipath signals which can becombined.

These techniques will maximize the Signal ToInterference Ratio (SIR)



SMDA



SPACE DIVISION MULTIPLE ACCESS

(SDMA) implies that more than one user can beallocated to the same physical communications

channel simultaneously in the same cell, onlyseparated by angle.

In a TDMA system, two users will be allocated to

the same time slot and carrier frequency at thesame time and in the same cell



Antenna Installation Considerations



Safety

standard operating procedure priority

Grounding

lightning strikes static charges

Surge protection

lightning searches for a second path to ground

Antenna Installation

Considerations-



Considerations

Adaptive array antenna placement needs to beconsidered differently than current technologiesserving the mobile environment.

They need to be placed so as to have a greater angular approach to the receiving units.

Existing tower placement with close proximity toroads and highways would need to bereconsidered.



Antenna Installation Considerations



Base, mast, and supportingstructure needs clearance,

serviceability (access), and

complies with the municipalguidelines (electrical and building

code)

Antenna selection



EEE381B

Selection of an appropriate antenna for a system

is highly application dependent

Factors include:

Angular coverage

Frequency of operation & bandwidth Polarization

Power gain

Antenna types]



EEE381B

Antenna types]

Angular

Coverage

Polarization Bandwidth Type

360°

azimuth

Linear Narrow

Wide

Whip, dipole, loop

Biconical, swastika

Circular Narrow

Wide

Helix

Conical spiral

Directional

Linear Narrow

Wide

Yagi, dipole array

Log periodic, horn, dish*

Circular NarrowWide

Horn with polarizer Cavity-backed spiral, dish*

* Dish characteristics depend on the feed



QUESTIONS?????

1. What are the two basic classifications of antennas?

2. What are the three parts of a complete antenna system?

3. What three factors determine the type, size, and shape of

an antenna?



an antenna?

4. If a wave travels exactly the length of an antenna fromone end to the other and back during the period of 1cycle, what is the length of the antenna?

5. What is the term used to identify the points of highcurrent and high voltage on an antenna?

6. What is the term used to identify the points of minimum

current and minimum voltage on an antenna?7. The various properties of a transmitting antenna can

apply equally to the same antenna when it is used as areceiving antenna. What term is used for this property?

8. The direction of what field is used to designate the

polarization of a wave?9. If a wave's electric lines of force rotate through 360

degrees with every cycle of rf energy, what is thepolarization of this wave?

ANSWERS:1. Half-wave (Hertz) and quarter-wave



(Marconi).2. Coupling device, feeder, and antenna.3. Frequency of operation of the transmitter,

amount of power to be radiated, and

general direction of the receiving set.4. One-half the wavelength.5. Current and voltage loops.6. Current and voltage nodes.

7. Reciprocity of antennas.8. Electric (E) field.9. Circular polarization.



ANSWERS:

10 V ti l l i ti



10. Vertical polarization.

11. Less interference is experienced by man-madenoise sources.

12. Vertical polarization.13. 73 ohms.

14. Anisotropic radiator.15. Isotropic radiator.16. Anisotropic radiator.17. Dipole, doublet and Hertz.18. Nondirectional.

19. Vertical plane.



ANSWERS:

20. The pattern would flatten.



p21. To connect one end through a capacitor to the

final output stage of the transmitter.22. A circular radiation pattern in the horizontal

plane, or same as a half wave.23. It is composed of a series of conductors

arranged in a radial pattern and buried 1 to 2feet below the ground.

24. Nine times the feed-point impedance.25. Folded dipole.

Problems:

1. A TV receiving antenna is to be constructed for channel 13. The spacing

between the reflector and dipole should be 2/10 of the wavelength. The



spacing between director and dipole should be 1/10 of a wavelength. The

length of the director is 5% shorter than the dipole and the reflector is 5%longer than the dipole. Determine the following: a. Length of the dipole; b.

Length of the reflector; c. Length of the director d. Spacing between the

dipole and the reflector; e. Spacing between the dipole and the director.

Note: the length of the dipole should be 5% shorter than λ/2 to

compensate for the “end effect” due to capacitance of the antenna.

2. A half-wave antenna has a center impedance of 70 ohms. It is coupled to

a flat 600 ohms transmission line through a quarter wavelength

transmission line. A. Determine the required impedance of the quarter wave section.; B. Determine the length of the quarter wavelength section

if it is constructed of an air insulated parallel line. Assume that the velocity

factor is 0.975 and the operating frequency of the antenna is 8 MHz.

Problems:

3. A 25 watt SSB transceiver operates on 10 KHz for a point



to point communication. A balanced open two-wire feeder

line spaced 10 inches apart with a wire diameter of 0.125

inch and a half dipole antenna is used for this system.

Determine a) Length of the antenna; b) system

wavelength; c) Zo of the feeder line; d) differentiate shortand long antenna

4. Calculate the length of the following antennas and state

their radiation resistance at 310 . a) dipole; b. Folded

dipole (twin lead; Z = 300 ohms; Vf= 0.8); c. Bow tieantenna (θ = 35 o; 0.73λ); d) ground plane vertical.



QUESTIONS ??????

Wavelength vs Physical Length



1. The speed of a radio wave: is the same as the

speed of light

2. The velocity of propagation of radio frequency

energy in free space is: 300 000 kilometers per

second3. If an antenna is made longer, what happens to its

resonant frequency? It decreases

4. If an antenna is made shorter, what happens to its

resonant frequency? It increases5. The resonant frequency of an antenna may be

increased by: shortening the radiating element


T l th t f f t th



1. To lower the resonant frequency of an antenna, the

operator should: lengthen it

2. Adding a series inductance to an antenna would:

decrease the resonant frequency


1. The wavelength for a frequency of 25 MHz is:



12 metres (39.4 ft)

1. The wavelength corresponding to a frequency of 2

MHz is:

150 m (492 ft)

1. At the end of suspended antenna wire, insulatorsare used. These act to: limit the electrical length

of the antenna

2. One solution to multi-band operation with a

shortened radiator is the "trap dipole" or trapvertical. These "traps" are actually: a coil and

capacitor in parallel

Gain, Directivity

1. What is meant by antenna gain?

The numerical ratio relating the radiated signal strength of an



The numerical ratio relating the radiated signal strength of anantenna to that of another antenna

1. The gain of an antenna, especially on VHF and above, is quoted in dBi.The "i" in this expression stands for: Isotropic

2. Approximately how much gain does a half-wave dipole have over anisotropic radiator? 2.1 dB

3. What is a parasitic beam antenna?

An antenna where some elements obtain their radio energy byinduction or radiation from a driven element

1. If a slightly shorter parasitic element is placed 0.1 wavelength away froman HF dipole antenna, what effect will this have on the antenna's radiationpattern? A major lobe will develop in the horizontal plane, toward theparasitic element

2. If a slightly longer parasitic element is placed 0.1 wavelength away from

an HF dipole antenna, what effect will this have on the antenna's radiationpattern? A major lobe will develop in the horizontal plane, away fromthe parasitic element, toward the dipole

Gain, Directivity

1. In free space, what is the radiation characteristic of ahalf-wave dipole? Minimum radiation from the ends,



maximum broadside

2. The front-to-back ratio of a beam antenna is: the ratioof the maximum forward power in the major lobe tothe maximum backward power radiation

3. The property of an antenna, which defines the range of

frequencies to which it will respond, is called its:Bandwidth

4. What is meant by antenna bandwidth? The frequencyrange over which the antenna may be expected toperform well

5. How can the bandwidth of a parasitic beam antenna beincreased? Use larger diameter elements

Vertical Antenna

1 To calculate the length in metres (feet) of a quarter wave



1. To calculate the length in metres (feet) of a quarter wave

vertical antenna you would : Divide 71.5 (234) by theantenna's operating frequency (in MHz)

2. If you made a quarter-wavelength vertical antenna for21.125 MHz, how long would it be? 3.6 metres (11.8 ft)

3. If you made a half-wavelength vertical antenna for 223MHz, how long would it be? 64 cm (25.2 in)

4. If a magnetic-base whip antenna is placed on the roof of a car, in what direction does it send out radio energy? It

goes out equally well in all horizontal directions

5. What is an advantage of downward sloping radials on aground plane antenna? It brings the feed pointimpedance closer to 50 ohms

Vertical Antenna1. What happens to the feed point impedance of a ground-

plane antenna when its radials are changed from horizontalto downward-sloping? It increases



to downward-sloping? It increases

2. Which of the following transmission lines will give the bestmatch to the base of a quarter-wave ground-plane antenna?50 ohms coaxial cable

3. The main characteristic of a vertical antenna is that it will:receive signals equally well from all compass pointsaround it

4. Why is a loading coil often used with an HF mobile verticalantenna? To tune out capacitive reactance

5. What is the main reason why so many VHF base and mobileantennas are 5/8 of a wavelength? The angle of radiationis low

6. Why is a 5/8-wavelength vertical antenna better than a 1/4-wavelength vertical antenna for VHF or UHF mobileoperations? A 5/8-wavelength antenna has more gain

Yagi Antenna1. How many directly driven elements do most Yagi antennas

have? One

2. Approximately how long is the driven element of a Yagi



2. Approximately how long is the driven element of a Yagiantenna for 14.0 MHz? 10.21 metres (33 feet and 6inches)

3. Approximately how long is the director element of a Yagiantenna for 21.1 MHz? 6.4 metres (21 feet)

4. Approximately how long is the reflector element of a Yagiantenna for 28.1 MHz? 5.33metres (17.5 feet long)

5. The spacing between the elements on a three-element Yagiantenna, representing the best overall choice, is : 0.2 of awavelength.

6. What is one effect of increasing the boom length and addingdirectors to a Yagi antenna? Gain increases

7. What are some advantages of a Yagi with wide elementspacing? High gain, less critical tuning and wider bandwidth

Wire Antenna

1 If you made a half wavelength dipole antenna for



1. If you made a half-wavelength dipole antenna for

28.550 MHz, how long would it be? 5.08 metres(16.62 ft)

2. What is the low angle radiation pattern of an ideal

half wavelength dipole HF antenna installed

parallel to the earth? It is a figure-eight,

perpendicular to the antenna

3. The impedances in ohms at the feed point of the

dipole and folded dipole are, respectively: 73 and300

Wire Antenna

1. A dipole transmitting antenna, placed so that theends are pointing North/South, radiates: mostly to



p g , y

the East and West2. How does the bandwidth of a folded dipole antenna

compare with that of a simple dipole antenna? It isgreater

3. What is a disadvantage of using an antennaequipped with traps? It will radiate harmonics

4. What is an advantage of using a trap antenna? Itmay be used for multi- band operation

5. What is one disadvantage of a random wireantenna? You may experience RF feedback inyour station

Quad / Loop antenna

1. What is a cubical quad antenna? Two or more parallel four-sided wire loops, each approximately one-electrical



sided wire loops, each approximately one electricalwavelength long

2. What is a delta loop antenna? A type of cubical quad antenna,except with triangular elements rather than square

3. The cubical "quad" or "quad" antenna consists of two or moresquare loops of wire. The driven element has an approximateoverall length of: one wavelength

4. The delta loop antenna consists of two or more triangular structures mounted on a boom. The overall length of the drivenelement is approximately: one wavelength

5. Approximately how long is each side of a cubical quad antennadriven element for 21.4 MHz? 3.54 metres (11.7 feet)

6. Approximately how long is each side of a cubical quad antenna

driven element for 14.3 MHz? 5.36 metres (17.6 feet)7. Approximately how long is each leg of a symmetrical delta loop

antenna driven element for 28.7 MHz? 3.5 metres (11.5 feet)

Quad / Loops

1. Which statement about two- element delta loops and quadantennas is true? They compare favorably with a three



antennas is true? They compare favorably with a three

element Yagi

2. Compared to a dipole antenna, what are the directionalradiation characteristics of a cubical quad antenna? Thequad has more directivity in both horizontal and

vertical planes

3. Moving the feed point of a multi-element quad antenna froma side parallel to the ground to a side perpendicular to theground will have what effect? It will change the antennapolarization from horizontal to vertical

Basics of _antennas (1)

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