Antennas

ANTENNASANTENNAS

A structure that is generally a metallic object, often a wire or group of wires, used to convert

high frequency signals into electromagnetic waves and vice

versa.

ANTENNA

A device whose function is to radiate

electromagnetic energy and/or

intercept electromagnetic

radiation

ANTENNA

Basic Consideration:

Maximum Power

Transfer

FIELDS OF AN ANTENNA

FIELDS OF AN ANTENNA

INDUCTION FIELDINDUCTION FIELD

Considered to extend out from the antenna

to a distance of D2/8λ

Near Field or Fresnel Region

RADIATION FIELDRADIATION FIELD

Considered to extend out from a distance of

2D2/λFar Field or

Fraunhoffer Region

TRANSITION ZONETRANSITION ZONEZone between the

two(2) regions

BASIC FORMULAS

ANTENNAS

T = 1/f

Where: T – time

F - frequency

λ = c/f

Where: λ – wavelength

F – frequency

C – velocity in free space

RADIATION PATTERN

ANTENNA PARAMETERS

A line drawn to join points in space which

have equal field intensity due to the

source.

RADIATION PATTERN

Major Lobe – the direction of maximum

radiationMinor Lobe – the

direction of minimum radiation

Null – the direction with radiation intensity

equal to zero.

a. Antenna a. Antenna heightheight

b. Power lossesb. Power losses

d. Thickness of the antenna d. Thickness of the antenna wirewire

RADIATION PATTERN

FACTORS WHICH DETERMINE THE RADIATION PATTERN OF

AN ANTENNA

c. Terminations at its c. Terminations at its endend

PRINCIPLE OF RECIPROCITYPRINCIPLE OF RECIPROCITY

The characteristics of antennas, such as impedance and radiation pattern are identical, regardless of use

for reception or transmission.

GENERAL CHARACTERISTICS OF ANTENNAS

ISOTROPIC ANTENNAISOTROPIC ANTENNA

An antenna that radiates uniformly in all directions in space

DIRECTIVE GAINDIRECTIVE GAIN

The ratio of the power density in a particular direction of one antenna to the power density that

would be radiated by an isotropic antenna.

HERTZIAN DIPOLE: 1.5 : 1 (1.76 dB)

HALF WAVE DIPOLE: 1.64 : 1 (2.15 dB)

GENERAL CHARACTERISTICS OF ANTENNAS

NOTESNOTES

The longer the antenna, the higher the directive gain

Non resonant antennas have higher directive gain than resonant antennas

GENERAL CHARACTERISTICS OF ANTENNAS

The directive gain of all practical antennas is greater than unity

DIRECTIVITY, DDIRECTIVITY, D

The gain in the direction of one of the major lobes in the antenna’s radiation pattern.

Maximum directive gain

GENERAL CHARACTERISTICS OF ANTENNAS

GENERAL CHARACTERISTICS OF ANTENNAS

POWER GAINPOWER GAIN

Overall gain considering losses and efficiency

Ap = %D

Where: % - antenna efficiency

D - directivity

ANTENNA RESISTANCEANTENNA RESISTANCE

The ratio of the applied voltage to the flowing current

AC resistance

GENERAL CHARACTERISTICS OF ANTENNAS

The ratio of the power radiated by the antenna to the square

1. RADIATION RESISTANCE, Rr1. RADIATION RESISTANCE, Rr

Antenna and ground resistance

Discharge or corona effects

GENERAL CHARACTERISTICS OF ANTENNAS

Losses in imperfect dielectric very near the antenna

Eddy current loss

2. LOSS RESISTANCE, Rd2. LOSS RESISTANCE, Rd

ANTENNA EFFICIENCYANTENNA EFFICIENCY

The ratio of the power radiated by the antenna to the power delivered at the

feedpointThe ratio of radiation resistance to the total

system resistance

GENERAL CHARACTERISTICS OF ANTENNAS

% = Rr / Rr + Rd

SAMPLE QUESTION

Ex. An antenna has a radiation resistance of 72 ohms, a loss resistance of 8 ohms, and a power gain of 16. What efficiency and directivity does it have.a. 90% and 17.78b. 10% and 160c. 90% and 160d. 10% and 17.78

REVIEW QUESTIONS

Ex. To produce a power density of 1 mw/m2 in a given direction, at a distance of 2 km, an antenna radiates a total of 180 w. An isotropic antenna would have to radiate 2400 w to produce the same power density at that distance. What, in dB, is the directive gain of the practical antenna?a. 11.25 dBb. 13.21 dBc. 10 dBd. 6 dB

EFFECTIVE EFFECTIVE RADIATED POWER RADIATED POWER

(ERP)(ERP)

The product of the power fed to an antenna and its power gain.

ERP = Total Radiated Power x Power Gain

The power radiated by an antenna in its favored direction, taking the gain of the antenna into

account as referenced to an isotropic radiator

EFFECTIVE EFFECTIVE ISOTROPIC RADIATED ISOTROPIC RADIATED

POWER (EIRP)POWER (EIRP)

GENERAL CHARACTERISTICS OF ANTENNAS

FRONT TO BACK RATIOFRONT TO BACK RATIO

Ratio of the power at the optimum direction of the antenna to that of the power 180

degrees from the optimum direction

The operating frequency range of an antenna

GENERAL CHARACTERISTICS OF ANTENNAS

BANDWIDTHBANDWIDTH

BEAMWIDTHBEAMWIDTH

Angular separation between two half power points in a major lobe of an

antenna radiation pattern

The degree of concentration of the antenna’s radiation

GENERAL CHARACTERISTICS OF ANTENNAS

POLARIZATIONPOLARIZATION

Space orientation of the waves that

the antenna radiates

The electric field vector is always parallel to the

antenna elements.

GENERAL CHARACTERISTICS OF ANTENNAS

FIELD STRENGTHFIELD STRENGTH

Radiated power per unit area

Is inversely proportional to the square of the distance from the

source.

GENERAL CHARACTERISTICS OF ANTENNAS

PHYSICAL PHYSICAL LENGTHLENGTH

Actual length of the antenna

λ/2 is the shortest length of a conductor which will resonate at

a given frequency

ANTENNA LENGTHS

L =λ/2; λ= c/f

ELECTRICAL LENGTHELECTRICAL LENGTH

Dependent upon the velocity coefficient or

velocity factor

The velocity factor is dependent upon the

ratio of the half wavelength to

conductor diameter

L = k λ

REVIEW QUESTIONS

EFFECTS OF GROUND ON EFFECTS OF GROUND ON ANTENNASANTENNAS

Whereas an ungrounded antenna with its image forms an antenna array, the bottom of the grounded

antenna is joined to the top of the image; the system acts as an antenna of double size.

GENERAL CHARACTERISTICS OF ANTENNAS

FUNCTIONS OF GROUNDFUNCTIONS OF GROUND

To help dissipate energy from lightning strikes  

EFFECTS OF GROUND ON ANTENNAS

To provide safety in case something tries to energize the chassis of equipment with dangerous voltages  

To provide a controlled RF return path for end-fed antennas  

To provide a highly conductive path for induced radio-frequency currents or fields rather than having them flow in lossy

EFFECTS OF GROUND ON EFFECTS OF GROUND ON ANTENNASANTENNAS

Whereas an ungrounded antenna

with its image forms an antenna array, the

bottom of the grounded antenna is joined to the

top of the image; the system acts as an

antenna of double size.

EFFECTS OF GROUND ON ANTENNAS

GROUND SCREENGROUND SCREEN

A network of buried wires directly under the antenna, consisting of a large number of radials

extending from the base of the tower, like spokes on a wheel, and placed 15 and 30 cm

below the ground

GROUNDING SYSTEMS

COUNTERPOISECOUNTERPOISE

A substitute for ground screen in areas of low conductivity, i.e. rock,

mountains and antennas on top of

buildings

GROUNDING SYSTEMS

ANTENNA HEIGHTANTENNA HEIGHT

The actual antenna height should at least be /4, but where this is

not possible, the effective height should

correspond to /4.

EFFECTS OF ANTENNA HEIGHT

TOP LOADINGTOP LOADING

A good method of increasing radiation resistance by having a

horizontal portion at the top of the antenna

EFFECTS OF ANTENNA HEIGHT

Effect: to increase the current at the base of the antenna and to

make the current distribution more uniform

EFFECTIVE EFFECTIVE LENGTHLENGTH

Antennas behave as though (electrically) they were longer

than their physical length

EFFECTS OF ANTENNA HEIGHT

The result of physical antennas having finite thickness, instead of

being infinitely thin.

END EFFECTEND EFFECT

ANTENNA ANTENNA COUPLINGCOUPLING

A network composed of reactances and

transformers, which may be lumped or

distributed, to provide impedance matching

COUPLING NETWORK

To tune out the reactive component of the antenna

impedance

REASONS FOR REASONS FOR COUPLINGCOUPLING

To provide the transmitter with the correct value of

load resistance

To prevent illegal radiation of spurious

frequencies

ANTENNA COUPLERSANTENNA COUPLERS

COUPLING NETWORK

The antennas are coupled directly to their transmitters

Affords a wider reactance range, giving adequate harmonic

suppression

Used for balanced lines

Direct CouplerDirect Coupler

CouplerCoupler

Symmetrical Symmetrical CouplerCoupler

IMPEDANCE MATCHINGIMPEDANCE MATCHING

IMPEDANCE MATCHING

Accomplished by connecting the coax or twin lead to the stub

and sliding the connections up or down the stub until the proper

SWR is indicated by a meter connected in the

system.

Stub Stub MatchingMatching

ANTENNA COUPLERSANTENNA COUPLERS

IMPEDANCE MATCHING

Accomplished by spreading the ends of the feedline and

adjusting the spacing until

optimum performance is

reached.

Delta MatchingDelta Matching

ANTENNA COUPLERSANTENNA COUPLERS

IMPEDANCE MATCHING

A sliding clamp is included in the

assembly to permit fine tuning for

minimum SWR at the time of installation

Gamma MatchingGamma Matching

ANTENNA COUPLERSANTENNA COUPLERS

IMPEDANCE MATCHING

A section of transmission line

one quarter wavelength long placed between the load and the

line

Quarter Wave Quarter Wave MatchingMatching

BalunBalun

Used to connect an unbalanced (coaxial line)

to a balanced antenna

CURRENT FED (LOW Z FEED)CURRENT FED (LOW Z FEED)

An antenna is said to be current fed if it is fed at the point of current maximum

SELECTION OF FEEDPOINT

Includes all feed point impedances below 600

ohms

Ex. Center fed half wave dipole or Marconi

antenna

VOLTAGE FED (HIGH Z FEED)VOLTAGE FED (HIGH Z FEED)

An antenna is said to be voltage fed if it is fed at the point of voltage maximum

SELECTION OF FEEDPOINT

Includes all feed point impedances in excess of 600

ohmsEx. Center fed full

wave dipole

1. A polar diagram or graph representing field strengths or power densities at various angular positions relative to an antenna.

a. Venn Diagramb. Figure 8 patternc. Lissajous figured. Radiation Pattern

REVIEW QUESTIONS

2. Refers to the orientation of the electric field radiated from an antenna.

a. radiationb. polarizationc. beamwidthd. bandwidth

REVIEW QUESTIONS

3. Pertains to a wire structure placed below the antenna and erected above the ground which is a form of capacitive grounding system.

a. imageb. counterpoisec. antenna orientationd. polarization

REVIEW QUESTIONS

4. What is the technique used to electrically increase the antenna length?

a. loadingb. using image antennac. using antenna arraysd. increasing antenna height

REVIEW QUESTIONS

5. Antenna supported by insulators seems electrically longer than its physical length due to

a. imageb. reflectionc. end effectd. broadside effect

REVIEW QUESTIONS

6. The ratio of the power radiated by the antenna to the total input power.

a. power gainb. directive gainc. antenna efficiencyd. radiation efficiency

REVIEW QUESTIONS

The ratio of the front lobe power to the back lobe power

front to side ratiofront to back ratioback to front ratio

minor to major ratio

REVIEW QUESTIONS

5What is the length of an antenna operating at a frequency of 500 kHz?

500 m570 m600 m630 m

REVIEW QUESTIONS

The gain of a hertzian dipole with respect to an isotropic antenna

1.76 dB2.15 dB1.5 dB1.64 dB

REVIEW QUESTIONS

A half wave dipole antenna is capable of radiating 2000 watts and has a 2.15 dB gain over an

isotropic antenna. How much power must be delivered to the isotropic antenna to match the

field strength of the directional antenna?1640 watts3280 watts4300 watts3520 watts

REVIEW QUESTIONS

5. Calculate the beamwidth between nulls of a 1m paraboloid reflector used at 6GHz.

3.5˚7˚

1.75˚14˚

REVIEW QUESTIONS

An antenna has a radiation resistance of 72 ohms, a loss resistance of 8 ohms and a power gain of 16.

What efficiency and directivity does it have?90% and 17.7810% and 17.7890% and 14.410% and 14.4

REVIEW QUESTIONS

Device that converts high frequency current into electromagnetic waves.

antennaloudspeakermicrophone

lightning arrester

REVIEW QUESTIONS

An ungrounded antenna near the groundacts as a single antenna of twice the height

is unlikely to need a ground screenacts as an antenna array

must be horizontally polarized

REVIEW QUESTIONS

Top loading is sometimes used with an antenna in order to increase itseffective height

bandwidthbeamwidth

input capacitance

REVIEW QUESTIONS

Very low signal strength in antennaminor lobes

nullsantenna patterns

major lobes

REVIEW QUESTIONS

A horizontal antenna is ______ polarized.vertically

horizontallycentrallycircularly

REVIEW QUESTIONS

Which of the following improves antenna directivity?driven element

reflectordirector

parasitic element

REVIEW QUESTIONS

What is the front to back ratio of an antenna which radiates 500 watts in a northernly direction and

50 watts in a southernly direction?25000 dB

10 dB100 dB20 dB

REVIEW QUESTIONS

If a 4 kw antenna produces 50 uV/m in a receiving antenna, a 16 kw will produce

200 uV/m10 uV/m100 uV/m20 uV/m

REVIEW QUESTIONS

If the radiated power increases 10.89 times, the antenna current increases by

3.3 times6.6 times1.82 times

10.89 times

REVIEW QUESTIONS

Shortening effect of an antenna that makes it appear as if it were 5% longer

end effectflywheel effect

skin effectcapture effect

REVIEW QUESTIONS

A simple half wavelength antenna radiates the strongest signal

at 45 degrees to its axisparallel to its axis

at right angles to its axisat 60 degrees to its axis

REVIEW QUESTIONS

If an antenna is too short for the wavelength being used, the effective length can be increased by

addingcapacitance in seriesinductance in seriesresistance in parallelresistance in series

REVIEW QUESTIONS

Actual height of an antenna should be at least1λλ/2λ/4¾ λ

REVIEW QUESTIONS

The directivity pattern of an isotropic radiatorfigure 8a sphere

unidirectional cardioidparabola

REVIEW QUESTIONS

Where are the voltage nodes in a half wave antenna?

at the endsthree quarters of the way from the feedpoint

towards the endone half of the way from the feedpoint towards the

endat the feedpoint

REVIEW QUESTIONS

A Herts antenna is operating on a frequency of 2182 kHz and consists of a horizontal wire that is

hanged between two towers. What is the frequency of its third harmonic?

727 kHz6546 kHz436 kHz

6.546 kHz

REVIEW QUESTIONS

What is the gain of an antenna over a half wavelength dipole when it has 6 dB gain over an

isotropic radiator?6 dB

8.1 dB3.9 dB10 dB

REVIEW QUESTIONS

Top loading is sometimes used with an antenna in order to increase itseffective height

bandwidthbeamwidth

input capacitance

REVIEW QUESTIONS

Top loading is sometimes used with an antenna in order to increase itseffective height

bandwidthbeamwidth

input capacitance

REVIEW QUESTIONS

Top loading is sometimes used with an antenna in order to increase itseffective height

bandwidthbeamwidth

input capacitance

REVIEW QUESTIONS

Top loading is sometimes used with an antenna in order to increase itseffective height

bandwidthbeamwidth

input capacitance

REVIEW QUESTIONS

Top loading is sometimes used with an antenna in order to increase itseffective height

bandwidthbeamwidth

input capacitance

REVIEW QUESTIONS

Top loading is sometimes used with an antenna in order to increase itseffective height

bandwidthbeamwidth

input capacitance

REVIEW QUESTIONS

Top loading is sometimes used with an antenna in order to increase itseffective height

bandwidthbeamwidth

input capacitance

REVIEW QUESTIONS

BASIC ANTENNAS

a standard reference antenna , radiating equally in all directions,

so that the radiation pattern is spherical.

ISOTROPIC ANTENNAISOTROPIC ANTENNA

ELEMENTARY DOUBLETELEMENTARY DOUBLET

A theoretical antenna shorter than a wavelength used as a standard to

which all other antenna characteristics can be compared

FIELD STRENGTH OF AN ELEMENTARY DOUBLET

= 60 le I sin = 60 le I sin θθ / / λλrr

Where

– antenna length

r – antenna length

Le – antenna length

I – antenna current

θθ – angle of axis and point of maximum radiation

REVIEW QUESTIONS

An elementary doublet is 10 cm long. If the 10 MHz current flowing through it is 2 A, what is the field strength 20 km away from the doublet in a direction of maximum radiation?

a. Announceb. Broadcastc. Transmitd. Media

BASIC ANTENNAS

An antenna made up of two wires bent at 90

degrees to each other so as to be in the same line and signal is fed at

the center

DIPOLEDIPOLE

DIPOLE

BASIC ANTENNAS

HALF WAVE DIPOLEHALF WAVE DIPOLE

Length is λ/2 and radiation pattern is a toroid (bidirectional)

DIPOLE

VOLTAGE AND CURRENT CHARACTERISTICS

VOLTAGEVOLTAGE CURRENTCURRENT

TYPES OF ANTENNAS

NON-RESONANT ANTENNANON-RESONANT ANTENNA

One in which there are no standing waves

Radiation pattern is directional

Standing waves are suppressed by the use of a

correct termination to ensure that no power is reflected, so that only a forward travelling

wave will exist.

NON-RESONANT ANTENNAS

LONG WIRE ANTENNALONG WIRE ANTENNA

Lengths in the order of several wavelengths

When an antenna is 2 or more wavelengths long, it provides gain and a multilobe radiation pattern. When terminated at

one end, it becomes unidirectional.

RHOMBIC ANTENNARHOMBIC ANTENNA

Consists of non-resonant antenna elements arranged differently, i.e.

planar rhombus

ANTENNA ARRAY

Length of equal radiators = 2 to 8 ‘s

Angle of tilt: 40 to 75

Rt = 800 ohms

Rin = 650 to 700 ohms

RHOMBIC ANTENNARHOMBIC ANTENNA

Non-resonant antenna used for long distance sky wave

transmission or reception of horizontally polarized waves over distances from 200 to

over 3000 miles at frequencies from 4 to 22 MHz.

NON-RESONANT ANTENNA

TYPES OF TRANSMITTER

RESONANT ANTENNARESONANT ANTENNA

Standing waves exist, caused by the presence of both a

reflected traveling wave and the forward wave.

Antenna whose length is a multiple of /4’s

RESONANT ANTENNA

HERTZ ANTENNAHERTZ ANTENNA

An antenna system in which the ground is not an essential

part

Half Wave Dipole

Half wave antenna used for frequencies above 2 MHz

RESONANT ANTENNA

MARCONI ANTENNAMARCONI ANTENNA

Grounded Quarter Wavelength antenna

Vertical Monopole

Quarter Wavelength antenna used for frequencies below 2

MHz; ominirectional

ANTENNA ARRAYANTENNA ARRAY

A radiating system consisting of

individual radiators or elements placed close together so as

to be within each other’s induction

field

ANTENNA ARRAY

DRIVEN ELEMENTDRIVEN ELEMENT

Element of an array connected to the output of the transmitter

ANTENNA ARRAY

Radiation not directly connected to the output of the transmitter

PARASITIC PARASITIC ELEMENTELEMENT

Receives energy through the induction field of a driven

element

REFLECTORREFLECTOR

A parasitic element longer than the driven element and close to it

reduces signal strength in its own direction and increases it in the

opposite direction.

ANTENNA ARRAY

DIRECTORDIRECTOR

A parasitic element shorter than the driven one from which it

receives energy; tends to increase radiation in its own direction

BROADSIDE ARRAYBROADSIDE ARRAY

Simplest array which consists of a number of dipoles of equal size,

equally spaced along a straight line with all dipoles fed in the same phase

from the same source.

ANTENNA ARRAY

Typical antenna length: 2 to 10 ‘s

Typical spacing: /2 or /4

Number of elements: dozens

ENDFIRE ARRAYENDFIRE ARRAY

Physical arrangement is the same as that of the

broadside array

ANTENNA ARRAY

The magnitude of the current in each element is still the same as in every other element, there is now a phase difference between these currents.

TURNSTILE ARRAYTURNSTILE ARRAY

Consists of two horizontal, half wave antennas mounted at right angles to each

other

ANTENNA ARRAY

YAGI UDA ANTENNAYAGI UDA ANTENNA

An array consisting of a driven element and one or more parasitic elements arranged collinearly and

close together.

ANTENNA ARRAY

FOLDED DIPOLEFOLDED DIPOLE

Single antenna which consists of 2 elements, one is fed directly and the other

coupled conductively at the ends.

ANTENNA ARRAY

LOG PERIODIC ANTENNALOG PERIODIC ANTENNA

Main feature is frequency independence for both radiation resistance and pattern

ANTENNA ARRAY

Bandwidths of 10:1 are achievable with ease

Radiation patterns: uni and bidirectional

LOG PERIODIC ANTENNALOG PERIODIC ANTENNA

Main feature is frequency independence for both radiation resistance and pattern

ANTENNA ARRAY

PYRAMIDAL ANTENNAPYRAMIDAL ANTENNA

a type of log periodic antenna

ANTENNA ARRAY

It looks and works in much the same way that a

standard lp antenna works, with one big difference: 

the two halves of the transmission line are

separated and positioned as a V, so each half of the

transmission line is in effect a single wire transmission line. 

PARABOLIC ANTENNAPARABOLIC ANTENNA

UHF AND MICROWAVE ANTENNAS

Parabola – a plane curve defined as the locus of a point which

moves so that its distance from another point (called the focus) plus its distance from a straight

line (directrix) is constant.

Works on the principle of a parabola

PARABOLIC ANTENNAPARABOLIC ANTENNA

UHF AND MICROWAVE ANTENNAS

All waves coming from the source and reflected

by the parabola will travel in the same

distance by the time they reach the directrix,

no matter from what point on the parabola

they are reflected.

CASSEGRAIN ANTENNACASSEGRAIN ANTENNA

TYPES OF FEED

an antenna in which the radiator is mounted at or near the surface of a concave main reflector and is aimed at a convex secondary reflector slightly inside the focus of the main reflector.

BEAMWIDTHBEAMWIDTH

PROPERTIES OF PARABOLIC REFLECTOR

Ф = 70λ / D Ф0 = 2 Ф

Where:

Ф0 = beamwidth between nulls, degrees

Ф = beamwidth between half power points, degrees

λ = wavelength, meters

D= mouth diameter, meters

GAIN OF A PARABOLIC ANTENNAGAIN OF A PARABOLIC ANTENNA

PROPERTIES OF PARABOLIC REFLECTOR

Ap = 6 ( D/λ)2

Where:

Ap = Power Gain

λ = wavelength, meters

D= mouth diameter, meters

1. Calculate the beamwidth between nulls of a 2-meter paraboloid reflector used at 6 GHz. Also, calculate the gain of the paraboloid reflector.

REVIEW QUESTIONS

HORN ANTENNAHORN ANTENNA

Ideal as primary feed antenna for parabolic reflectors and

lenses

UHF AND MICROWAVE ANTENNAS

LENS LENS ANTENNAANTENNAUsed as a collimator of

frequencies in excess of 3 GHz

UHF AND MICROWAVE ANTENNAS

HELICAL ANTENNAHELICAL ANTENNA

A broadband VHF and UHF antenna which used when it is

desired to provide circular polarization characteristics

UHF AND MICROWAVE ANTENNAS

Consists of a loosely wound helix backed up by a ground plane,

which is simply a screen made of chicken wire

DISCONE ANTENNADISCONE ANTENNA

A combination of a disk and a cone in close proximity

UHF AND MICROWAVE ANTENNAS

Characterized by an enormous bandwidth for both input

impedance and radiation pattern

A constant angle, low gain antenna; omnidirectional

LOOP ANTENNALOOP ANTENNA

Used for direction finding, because they do not

radiate in a direction at right angles to the plane of

the loop

UHF AND MICROWAVE ANTENNAS

For portable domestic receivers

Circular or square shaped

PHASED ARRAYPHASED ARRAY

Group of antennas, connected to one transmitter or receiver, whose radiation beam can be adjusted electronically without physically moving parts; used

in radars.

RADAR ANTENNA

PHASED ARRAYPHASED ARRAY

Group of antennas, connected to one transmitter or receiver, whose radiation beam can be adjusted electronically without physically moving parts; used

in radars.

RADAR ANTENNA

WHIP ANTENNAWHIP ANTENNA

whip antenna is the most common example of a monopole antenna, an antenna with a single driven element and a ground plane.The whip antenna is a stiff but flexible wire mounted, usually vertically, with one

end adjacent to a ground plane..

RADAR ANTENNA

WHIP ANTENNAWHIP ANTENNA

whip antenna is the most common example of a monopole antenna, an antenna with a single driven element and a ground plane.The whip antenna is a stiff but flexible wire mounted, usually vertically, with one

end adjacent to a ground plane..

RADAR ANTENNA

POLEPOLE

Used to signify one piece of structure similar to the common telephone pole

ANTENNA SUPPORTING STRUCTURES

ANTENNA SUPPORTING STRUCTURES

Used to designate a structure made of metal or wood which may be

either in a form of a one piece or sectionalized structure

MASTMAST

TOWERTOWER

Applied to a very large, high structure, which in

most cases, is constructed of metal

ANTENNA SUPPORTING STRUCTURES

1. A non-resonant antenna that is capable of operating satisfactorily over a relatively wide bandwidth, making it ideally suited for HF transmission.

a. end-fire arrayb. rhombicc. broadside arrayd. log periodic

2.

REVIEW QUESTIONS

Antenna that is independent of their radiation resistance and radiation pattern to frequency. It has bandwidth ratios of 10:1

or greater.a. loop antenna

b. helicalc. Yagi Uda antennad. Log periodic antenna

REVIEW QUESTIONS

A half wave antennaHertz

MarconiParabolic

Vertical Monopole

REVIEW QUESTIONS

Antenna which is used very frequently but almost entirely as a reception antenna and is usually found at the back of table radios.

loop antennafolded antenna

rhombiclog periodic

REVIEW QUESTIONS

One of the special purpose antennas which has broadband VHF and UHF that is ideally suited for applications for which radiating circular

rather than horizontal or vertical polarized electromagnetic waves are required.

loop antennaphased arrayfolded dipole

helical

REVIEW QUESTIONS

What are the two types of antenna elements?driven and reflector

director and reflectorparasitic and directordriven and parasitic

REVIEW QUESTIONS

Which one of the following terms does not apply to the Yagi Uda array?

good bandwidthparasitic elements

folded dipolehigh gain

REVIEW QUESTIONS

Indicate the antenna that is not wideband.discone

folded dipolehelical

Marconi

REVIEW QUESTIONS

One of the following is not an omnidirectional antennahalfwave dipole

log periodic antennadisconbeMarconi

REVIEW QUESTIONS

One of the following consists of nonresonant antennasrhombic

folded dipoleend fire array

broadside array

REVIEW QUESTIONS

Which of the following is best excited from a waveguide?biconical

hornhelicaldiscone

REVIEW QUESTIONS

An antenna that is circularly polarizedparabolic reflector

Yagi UdaHelical

Circular loop

REVIEW QUESTIONS

What is the polarization of a discone antenna?vertical

horizontalcircularspiral

REVIEW QUESTIONS

When speaking of antennas, ____ is a section which would be a complete antenna by itself.

imagetop loading

bayquarterwave

REVIEW QUESTIONS

______ is an antenna with a number of half wave antennas in it.

antenna arraytower

omnidirectionalrhombic

REVIEW QUESTIONS

Which antenna radiates an omnidirectional pattern in the horizontal plane with vertical

polarization?MarconiDiscone

HornHelical

REVIEW QUESTIONS

An antenna with very high gain and very narrow beamwidth.

helicaldiscone

hornparabolic dish

REVIEW QUESTIONS

An open ended slot antennahelical

rhombicnotch

cassegrain

REVIEW QUESTIONS

Which antenna is properly terminated?MarconiRhombicDipole

Yagi Uda

REVIEW QUESTIONS

33. In a standard commercial TV broadcast, the picture carrier signal is located _____ above the lower end frequency of the channel.a. 0.75 MHzb. 0.25 MHzc. 4.2 MHzd. 1.25 MHz

34. Special effects and production switching are done by the a. CCUb. ENGc. SEGd. Sync Gen

REVIEW QUESTIONS

35. The hue 180 degrees out of phase with red isa. cyanb. yellowc. greend. Magenta

36. Greater peak to peak amplitude of the 3.58 MHz chrominance signal indicates morea. whiteb. yellowc. hued. saturation

What is the radiation characteristic of a dipole antenna?

omnidirectionalbidirectionalunidirectionalhemispherical

REVIEW QUESTIONS

An antenna with unity gain.rhombic

half wave dipoleisotropic

whip

REVIEW QUESTIONS

An antenna which is one tenth wavelength long.hertz antennaloop antenna

Marconi antennaElementary doublet

REVIEW QUESTIONS

What is the minimum number of turns a helical antenna must have?3456

REVIEW QUESTIONS

An antenna made up of a number of full wavelengths

elementary doubletlog periodiclong wire

whip

REVIEW QUESTIONS