Basic Antenna Theory & Communications Antenna System

ComeC 513 2013

AgendaAntenna definitionAntenna theoryAntenna parametersTypes of AntennaApplications

IntroductionAnANTENNAis a conductor, or system of conductors, that radiates or receives energy in the form of electromagnetic waves.

Transmission - radiates electromagnetic energy into spaceReception - collects electromagnetic energy from space

The antenna converts radio frequency electrical energy fed to it (via the transmission line) to an electromagnetic wave propagated into space.

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

Antenna Definition-contdIn transmit systems the RF signal is generated, amplified, modulated and applied to the antennaIn receive systems the antenna collects electromagnetic waves that are cutting through the antenna and induce alternating currents that are used by the receiver

Antenna TypesHigh Frequency1.6 - 30 Mhz + 50 Mhz160 - 6 meters

An antennas size/length depends on the frequencyIts functionality largely depends on the height above ground, as well as the polarity and its configuration

AntennasA good antenna worksA bad antenna is a waste of time & moneyAntenna systems can be very inexpensive and simpleThey can also be very, very expensiveAntenna ConsiderationsThe space available for an antennaThe proximity to neighborsThe operating frequencies you will useThe output powerMoney

Isotropic AntennaThe 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 practicalThe pattern is a Cardioid - a donut shape or a sphere

Current and voltage distribution on an antenna.

A current flows in the antenna with an amplitude that varies with the generator voltage.

A sinusoidal distribution of charge exists on the antenna. Every 1/2 cycle, the charges reverse polarity.

The sinusoidal variation in charge magnitude lags the sinusoidal variation in current by 1/4 cycle.

Standing waves of voltage and current on an antenna.

ReciprocityAn 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

RECIPROCITYof antennas means that the various properties of the antenna apply equally to transmitting and receiving

PolarizationPolarization is the direction of the electric field and 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 surfaceHorizontal waves travel parallel to the earths surfaceUsually wire antennas are horizontal but an inverted V dipole has a vertical componentYagi type antennas can be either vertical or horizontalCircular antennas can be both vertical and horizontalUsually, horizontally polarized antennas receives less noise

Terms And DefinitionsRADIATION RESISTANCEis 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 PATTERNScan be plotted on a rectangular- or polar-coordinate graph. These patterns are a measurement of the energy leaving an antenna.

Dipole antenna

EEE381BDipole AntennaCharacteristicsPolarization: verticalBeamwidth: 80 x 360Bandwidth: 10%Gain: 2 dBTypical ApplicationsTV Rabbit earsFM radio (folded dipole)Radio mast transmitters

EEE381BSimplified Radiation PatternsElevation, ElAzimuth, Az

3-D pattern

Antenna radiation pattern is 3- dimensional

The 3-D plot of antenna pattern assumes both angles and varying, which is difficult to produce and to interpret 3-D pattern

Source: NK Nikolova

Reference antenna (/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:Directional- 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 antennaeOmni-Directional- 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 PatternRadiation pattern is an indication of radiated field strength 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 PatternsRadiation patternGraphical representation of radiation properties of an antennaDepicted as two-dimensional cross sectionBeamwidth (or half-power beam width) Measure of directivity of antennaReception patternReceiving antennas equivalent to radiation pattern

Radiation Pattern for Vertical Antennasantenna/4/2

Antenna Radiation PatternsCommon parameters main lobe (boresight) half-power beamwidth (HPBW) front-back ratio (F/B) pattern nullsTypically measured in two planes: Vector electric field referred to E-field Vector magnetic field referred to H-field

Typical Radiation Pattern for an Omni

ALOBEis the area of a radiation pattern that is covered by radiation.

ANULLis the area of a radiation pattern that has minimum radiation.

BeamwidthBeamwidth is the angular separation of the half-power points of the radiated pattern

beamwidthantennaAPower 3dB down from maximum point AMax power2 dipoleDirectional AntennaRadiated energy is focused in a specific direction

TYPES OF ANTENNASIsotropic antenna (idealized)Radiates power equally in all directionsDipole antennasHalf-wave dipole antenna (or Hertz antenna)Quarter-wave vertical antenna (or Marconi antenna)Parabolic Reflective Antenna

Antenna HERTZ(half-wave) andMARCONI(quarter-wave) are the two basic classifications of antennas.

HERTS ANTENNAOR HALFWAVE DIPOLE -consists of two lengths of rod or tubing, each a quarter-wave long at a certain frequency, which radiates 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 the antenna to represent a half-wave.

AQUARTER-WAVE ANTENNA(Marconi) is a antennna (total of half-wave antenna) cut in half with one end grounded. Also called Vertical Antennas are used for frequencies under 2 MHz. It uses a conducting path to ground that acts as wavelength portion the antenna above the ground. The above ground structure represents a /4 wavelength

Types of AntennasSimple wire Dipole Folded dipole Trap dipole Offset or Windom antenna Phased dipoles Vertical or horizontal (both) Beverage wave antenna

Types of AntennasMetalVerticalYagiTrap YagiPhased arraysLoopsVertical or HorizontalHorns for super ultra high frequenciesMobile antennas

Horizontal and Dipole Antennas*A horizontal antenna is an antenna that is a simple dipole mounted so the elements are parallel to the earth's surface. So whats a dipole?A dipole antenna consists of two sections that are each approximately one-quarter of the wavelength of that band, so that the total length is equal to about one-half wavelength. It is a simple antenna designed to work best on a single band.

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

Dipole Antenna*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, the dipole 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 to work their best. In a fixed station, a vertical may either be mounted on the ground or on a mast, and it may also have several radials for counterpoise. These radials may be laid out on the ground, as in the next slide, or mounted just underneath the vertical element, as in an elevated ground plane. In a mobile installation, the metal body of the car usually serves as the counterpoise.

Vertical (Marconi) Antenna contdPoor grounding conditions of the earth/soil surrounding the antenna can result in serious signal attenuation.

This problem is alleviated by installing a counterpoise

CounterpoiseCounterpoise 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-contdsupportsantennaradius =

Typical Ground-Mounted Vertical*This is a rough diagram of a ground-mounted vertical. The orange radials you see may be laid along the top of the ground or buried just beneath the surface.

TheGROUND SCREENand theCOUNTERPOISEare used to reduce losses 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*Ground plane antenna another type of vertical antenna. It is designed to be mounted on a mast, and usually has three or four radials coming from the base of the antenna.

EEE381BWhip AntennaElAzCharacteristicsPolarization: verticalBeamwidth: 45 x 360Bandwidth: 10%Gain: 0 dBTypical ApplicationsAutomobile radio and satellite signalsMilitary (army) communications

EEE381BLoopElAzCharacteristicsPolarization: horizontalBeamwidth: 80 x 360Bandwidth: 10%Gain: -2 dBTypical ApplicationsAM Broadcasting

TheFOLDED DIPOLEconsists of a dipole radiator, which is connected in parallel at its ends to a half-wave radiator.

ALONG-WIRE ANTENNAis 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 ANTENNASconsist of a single wire that is two or more wavelengths long.

AV ANTENNAis a bidirectional antenna consisting of two horizontal, long wires arranged to form a V.

TheRHOMBIC ANTENNAuses four conductors joined to form a rhombus shape. This antenna has a wide frequency range, is easy to construct and maintain, and is noncritical as far as operation and adjustment are concerned.

HelicalEl & AzCharacteristicsPolarization: circular (axial mode)Beamwidth: 50 x 50Bandwidth: 70%Gain: 10 dBTypical ApplicationsMobile communicationsGPSSpace communication Animal tracking

TheTURNSTILE ANTENNAconsists of two horizontal, half-wire antennas mounted at right angles to each other.

ANTENNA LOADINGis the method used to change the electrical length of an antenna.

This keeps the antenna in resonance with the applied frequency. It is accomplished by inserting a variable inductor or capacitor in series with the antenna.

Antenna ArrayAntenna 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.

ANARRAYis a combination of half-wave elements operating together as a single antenna. It provides more gain and greater directivity than single element antennas.

ADRIVEN ARRAYderives its power directly from the source.APARASITIC ARRAYderives its power by coupling the energy from other elements of the antenna.

TheBIDIRECTIONAL ARRAYradiates energy equally in two opposing directions.TheUNIDIRECTIONAL ARRAYradiates energy efficiently in a single direction.

TheCOLLINEAR ARRAYhas elements in a straight line. Maximum radiation occurs at right angles to this line.TheBROADSIDE ARRAYhas elements parallel and in the same plane. Maximum radiation develops in the plane at right angles to the plane of the elements.

TheBROADSIDE ARRAYhas elements parallel and in the same plane. Maximum radiation develops in the plane at right angles to the plane of the elements.

TheEND-FIRE ARRAYhas elements parallel to each other and in the same plane. Maximum radiation occurs along the axis of the array.

Phased ArrayElAzCharacteristicsPolarization: linear / circularBeamwidth: 0.5 x 30Bandwidth: variesGain: 10 to 40 dBTypical ApplicationsRadio broadcastingSearch & track radarWeather radar (severe storm watch)

Military Phased Array Usage

Phased array antennasPhased array antennas have become an extremely important type of radar for military use, particularly airborne use.In radar applications, phased arrays permit near instant switching from one target to another, and from search to track mode.Phased arrays combined with smart skin technology have radically altered airborne avionics designs.

EEE381BBasic phased array architectureSignal Divider / CombinerSteering angle, sElement spacing

EEE381B

EEE381BPhased array gainThe gain of a phase array antenna is a function of the number of elements in the array and the gain of the individual elements

For half-wavelength element spacing, the gain at boresight is given by:G = 10 log (N) + Ge The gain off-boresight is reduced by the cosine of the steering angle, s:G = 10 log (N) + Ge + 10 log (cos s)

EEE381B

EEE381BPhased array beamwidthThe beamwidth of a phased array antenna is a function of the number of elements.For a half-wavelength phased array of dipole elements the half-power beamwidth is given by:

3-dB B = 102/N where N = no. of arrays

The beamwidth at off-boresight steering angles increases with the cosine of s :

3-dB B = (102/N) / cos(s)

EEE381B

EEE381BBeam steering limitationsA phased array antenna with half-wavelength spacing is limited to beam steering angles of 45 off boresight.

Greater steering angles can be achieved by reducing the element separation at the expense of boresight gain.

EEE381B

Pointers in antenna design:

MATCHING STUBSare used between elements to maintain current in the proper phase.

TheGAIN OF A COLLINEAR ANTENNAis greatest when the elements are spaced from 0.4 to 0.5 wavelength apart or when the number of elements is increased.

TheOPTIMUM GAIN OF A BROADSIDE ARRAYis obtained when the elements are spaced 0.65 wavelength apart.

APARASITIC ARRAYconsists of one or more parasitic elements with a driven element. The amount of power gain and directivity depends on the lengths of the parasitic elements and the spacing between them.

ARRAYS, such as the YAGI, have a narrow Frequency response as well as a narrow beamwidth.

Yagi-Uda AntennaThe Yagi-Uda antenna is a simple form of a directional antenna based on a reflector placed /4 from the dipole antenna placement.

Yagi-Uda Antenna-contdreflector/2dipole antenna/4

antenna2 dipole radiated signal without reflector2 dipole radiated signal with reflectorRadiated Directed Signal

The Antenna Formula c f = frequency of the signalc = 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 be constructed for a 60 Hz signal, how large would it need to be? c 186,000 misec60= 3100 mi2 = 1550 miles!

Radiation & Induction FieldsThe mechanics launching radio frequencies from an antenna are not fully understood. The RF fields that are created around the antenna have specific properties that affect the signals transmission. The radiated field is known as the radiation field

Radiation & Induction Fields-contdThere are two induction fields or areas where signals collapse and radiate from the antenna. They are known as the near field and far field. The distance that antenna inductance has on the transmitted signal is directly proportional to antenna height and the dimensions of the wave.R 2D2

Radiation & Induction Fields-contdR 2D2Where: R = the distance from the antennaD = dimension of the antenna = wavelength of the transmitted signal

Radiation ResistanceRadiation Resistance is the portion of the antennas 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 ImpedanceA proper Impedance Match is essential for maximum power 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

Point-Source RadiatorConsider 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 PT .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 4d2.

Power Concentrator If a reflector were added to the point source, more of the power would go in one direction that the others.

This increase in power (over isotropic) can be expressed as the power gain GT of the antenna.

Since the antenna is a passive device, it cannot actually increase the total power radiated.

The higher the gain of the antenna, the more focused is the power in one direction.

The gain only applies along the bore sight of the antenna.

Antenna Gain The antenna power gain is defined as

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

Effective Isotropic Radiated PowerThe Effective Isotropic Radiated Power (EIRP) of an antenna is power input required of an isotropic antenna to produce the same power density on the bore sight as the actual antenna.PERIP = PT GTPower Density at d = (PERIP )/ (4d2) = (PT GT )/(4d2) (w/m2)

d = distance from the antennaThe EIRP is the transmitted power multiplied by the gain of the transmitting antenna.

Effective Radiated Power (ERP)ERP = the power input value multiplied by the gain of the antenna

dBi = isotropic radiator gaindBd = dipole antenna gain

Effective AreaIf the receiving antenna is placed d meters from the transmitting antenna, it will act like a catchers 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 with respect to that which would be radiated by a reference antenna

Antenna Gain

Directive Gain ratio of the power density in a particular direction of one antenna to the power density that would be radiated by an omnidirectional antenna (isotropic antenna).

Directivity refers to the ability of an antenna to send and/or receive signals over a narrow horizontal directional range.

Gain of Hertzian Dipole with respect to an isotropic antenna = 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 isotropic antenna = 1.64:1 or 10 log 1.64 = 2.15 dB.

Antenna Gain Relationship between antenna gain and effective area

G = antenna gainAe = effective areaf = carrier frequencyc = speed of light (3 X 108 m/s) = carrier wavelength

Antennas GainGainThe power gain, G, of an antenna is very much like its directive gain, but also takes into account efficiencyThe maximum power gain The maximum power gain is often expressed in dB.

Antenna HeightAntenna height above the ground is directly related to radiation 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 antennas are approximately 95% of the physical length. Ideal antenna height is usually based on trial and error procedures

Dipole Length:

Antenna is a frequency sensitive device. = c/f = 984/f(MHz); /2 = 492/f(MHz) (feet)

Example:

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

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

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

Antenna Q and Bandwidth:

Bandwidth is determined by the frequency of operation while Q is the quality 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 the diameter of the conductor. Also affected by the number of conductors used and their spacing to the dipole.

Q= XL / RBW = F/QNote: 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.

= 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 feetProblem:

Determine the length of an antenna operating at frequency 500 KHz.

Antenna Characteristics:

The longer the antenna length, the higher the directive gain. HW dipole Gain = 1.64 (2.15dB); 8 dipole Gain = 7.1 (8.51dB)2. Non-resonant antenna have higher directive gain than resonant antenna.

Non-resonant Antenna (Directional Antenna) similar to a properly terminated transmission line, produces no standing waves. Reflected waves are suppressed by the terminating resistance (resistor) at the point farthest from the feed point.

Resonant Antenna standing waves exist; a multiple of half-wavelenghts of the signal frequency.

Directivity and Power Gain

Power Gain comparison of the output power of an antenna in a certain direction to that of an isotropic antenna.

Antenna Gain is the power ratio comparison between an omnidirectional and unidirectional radiator.

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

Where: P1 = power of unidirectional antenna

P2 = 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-kW and has a 2.15 dB gain over an isotropic antenna. How much 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 antenna 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 xmission line 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

Field Intensity the field of an antennas radiation at a given point in space, is equal to the amount of voltage induced in a wire antenna 1 meter long, located a that given point.

Factors affecting FI: time, atmospheric condition and distance.

Antenna Resistance hypothetical value which, if replaced by an equivalent resistor, would dissipate exactly the same amount of power that the antenna would radiate. This is the ration of the power radiated by the antenna to the square 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 antenna itself.

Pin = Pd + Prad Pin power delivered to the feed point Pd power lost Prad power actually radiated

I2 Rin = I2Rd + I2RradRin = Rd+ Rrad

Antenna Efficiency = = (Rrad / (Rd + Rrad )

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

Antennas EfficiencyPower is fed to an antenna through a T-Line and the antenna appears as a complex impedanceEfficiencywhere the antenna resistance consists of radiation resistance and and a dissipative resistance.The power dissipated by ohmic losses isThe power radiated by the antenna isAn Antenna Efficiency e can be defined as the ratio of the radiated power to the total power fed to the antenna.For the antenna is driven by phasor current

ExampleSuppose an antenna has directivity (gain) D = 4, Rrad = 40 and Rdiss = 10 . Find antenna efficiency and maximum power gain.

Antenna efficiency isMaximum power gain isMaximum power gain in dB is

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 is Vertically Polarized.PolarizationNo matter what polarity you choose, all antennas in the 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

More on Dipoles*Dipoles may be mounted either horizontally or vertically, depending on the intended use. May be made from wire or metal tubing, and are very easy for a new ham to construct. Wire dipoles are also fairly inexpensive and simple to design.

With an antenna tuner, they can also be made to work on several bands. For these reasons, they are very popular with new hams (amateur radio) on the HF bands.

Beam Antennas*A beam antenna is an antenna that concentrates signals in one direction.

It is designed to focus all of the energy produced by your transmitter in the direction you want to work. Focusing your signal power in one direction makes for a stronger signal in that direction. Beams are effective, but depending on the bands covered and type, they can be expensive.

Beam Antennas - Quad*The quad, Yagi, and dish are all examples of beam antennas. A quad antenna looks something like a metal frame for a box kite. If you look closely, you can see the antenna wires supported by the X framework.

Quad antenna

Beam Antennas - Yagi*The yagi is a one dimensional beam antenna consisting of several elements. It may be mounted horizontally, as shown here, or vertically.

EEE381BLog PeriodicCharacteristicsPolarization: vertical / horizontalBeamwidth: 80 x 60Bandwidth: 10 to 1Gain: 6 to 8 dBTypical ApplicationsAmateur radio

EEE381BYagiCharacteristicsPolarization: horizontalBeamwidth: 90 x 50Bandwidth: 5%Gain: 5 to 15 dBTypical ApplicationsWWII airborne radarAmateur 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

EEE381BCavity Backed SpiralEl & AzCharacteristicsPolarization: circularBeamwidth: 80 x 80Bandwidth: 9 to 1Gain: -15 to +3 dBTypical ApplicationsRadar altimeterElectronic warfare

EEE381BConical SpiralEl & AzCharacteristicsPolarization: circularBeamwidth: 60 x 60Bandwidth: 4 to 1Gain: 5 to 8 dBTypical ApplicationsGround penetrating radarElectronic warfare

EEE381BHornElAzCharacteristicsPolarization: linear / circularBeamwidth: 40 x 30Bandwidth: 4 to 1Gain: 4 to 10 dBTypical ApplicationsRadio astronomyElectronic warfareAntenna testing

EEE381BLargest Horn AntennaIt was from this historic radio astronomy horn antenna that microwave background radiation was discovered, helping to confirm the Big Bang theory

Beam Antennas - Dish*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 Dish Network antennas.

EEE381BParabolicEl & AzCharacteristicsPolarization: depends on feedBeamwidth: 0.5 x 30Bandwidth: variesGain: 10 to 55 dBTypical ApplicationsSatellite TVCellular telephony, Wi-FiRadio astronomySearch & track radar

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 /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

THE CASEGRAIN ANTENNA

In telecommunication and radar use, a Cassegrain antenna is an antenna in which 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

What is an isotropic antenna? hypothetical point sourceDescribe the antenna radiation pattern for an isotropic radiator? A sphereWhat determines the polarization of an antenna? the electric fieldWhat does horizontal wave polarization mean? The electric lines of force of the radio wave is parallel to the earth's surfaceWhat does vertical wave polarization mean? The electric lines of force of a radio wave are perpendicular to the earth's surface

What electromagnetic wave polarization does a Yagi antenna have when its elements are parallel to the earth's surface? HorizontalWhat electromagnetic wave polarization does a half-wavelength antenna have when it is perpendicular to the earth's surface? VerticalVHF signals from a mobile station using a vertical whip antenna will normally be best received using a: vertical ground-plane antennaA dipole antenna will emit a vertically polarized wave if it is: Parallel with the ground mounted verticallyIf an electromagnetic wave leaves an antenna vertically polarized, it will arrive at the receiving antenna, by ground wave: vertically polarizedCompared with a horizontal antenna, a vertical antenna will receive a vertically polarized radio wave: at greater strength

*Microwave Parameters:General Equation: B. Parabolic Antenna Gain, Gwhere:D = antenna diameter in m = signal wavelength in m = efficiency

*Microwave Parameters:Antenna Gain for Typical Values of (0.55 to 0.75): Parabolic Antenna Gain for Typical Values of (0.55 to 0.75) in Metric system:

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

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 the cellular telephone system``

Typical Radiation Pattern for a Sector

Beamforming Antenna

Beamforming Antenna Array

Smart Antennas

SMART ANTENNAA smart antenna is a digital wireless communications antenna system that takes advantage of diversity effect at the source (transmitter), the destination (receiver), or both.

Diversity effect involves the transmission and/or reception of multiple radio frequency (RF) waves to increase data speed and reduce the error rate.

SMART ANTENNASmart antennas fall into three major categories: SIMO (single input, multiple output), MISO (multiple input, single output), and 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 at the source, and one antenna is used at the destination. In MIMO technology, multiple antennas are employed at both the source and the destination. MIMO has attracted the most attention recently because it can not only eliminate the adverse effects of multipath propagation, but in some cases can turn it into an advantage.

Smart AntennasSmart antennas (also known as adaptive array antennas, multiple antennas and, recently, MIMO)

are antenna arrays with smart signal processing algorithms used to identify spatial signal 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 AntennasSmart Antennas are base station antennas with a pattern that is not fixed, but adapts to the current radio conditionsSmart 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 AntennasThe idea of smart antennas is to use base station 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 onlySmart antenna techniques are used notably in acoustic signal processing, track and scan RADAR, radio astronomy and radio telescopes, and mostly in cellular systems like W-CDMA and UMTS.

Smart AntennasSmart antennas add a new way of separating users, 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 communication link can be significantly improved

Smart Antenna

Elements of a Smart AntennaSmart antennas consists of a number of radiating elements, a combining/dividing network and a control unit

Phased Array AntennaPhased Array antennas are a combination of antennas in which there is a control of the phase and power of the signal applied at each antenna resulting in a wide variety of possible radiation patterns

Types of Intelligent AntennasSwitched lobe (SL): This is also called switched beam. It is the simplest technique, and comprises only a basic switching function between separate directive antennas or predefined beams of an array. The setting that gives the best performance, usually in terms of received power, is chosen

Intelligent Antennas-Dynamically phased array (PA):

By including a direction of arrival (DoA) algorithm for the signal received from the user, continuous tracking 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 out the interferers. In addition, by using special algorithms and space diversity techniques, the radiation pattern can be adapted to receive multipath signals which can be combined. These techniques will maximize the Signal To Interference Ratio (SIR)

SMDASPACE DIVISION MULTIPLE ACCESS (SDMA) implies that more than one user can be allocated to the same physical communications channel simultaneously in the same cell, only separated by angle.

In a TDMA system, two users will be allocated to the same time slot and carrier frequency at the same time and in the same cell

SMDA-In systems providing full SDMA, there will be much more intracell handovers than in conventional TDMA or CDMA systems, and more monitoring by the network is necessary

Antenna Installation ConsiderationsSafetystandard operating procedure priorityGroundinglightning strikesstatic chargesSurge protectionlightning searches for a second path to ground

Antenna Installation Considerations-Adaptive array antenna placement needs to be considered differently than current technologies serving 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 to roads and highways would need to be reconsidered.

Antenna Installation ConsiderationsBase, mast, and supporting structure needs clearance, serviceability (access), and complies with the municipal guidelines (electrical and building code)

EEE381B Antenna selectionSelection of an appropriate antenna for a system is highly application dependentFactors include:Angular coverageFrequency of operation & bandwidthPolarizationPower gain

EEE381B

EEE381BAntenna types]* Dish characteristics depend on the feed

Angular CoveragePolarizationBandwidthType360 azimuthLinearNarrowWideWhip, dipole, loopBiconical, swastikaCircularNarrowWideHelixConical spiralDirectionalLinearNarrowWideYagi, dipole arrayLog periodic, horn, dish*CircularNarrowWideHorn with polarizerCavity-backed spiral, dish*

QUESTIONS?????

What are the two basic classifications of antennas?What are the three parts of a complete antenna system?What three factors determine the type, size, and shape of an antenna?If a wave travels exactly the length of an antenna from one end to the other and back during the period of 1 cycle, what is the length of the antenna?What is the term used to identify the points of high current and high voltage on an antenna?What is the term used to identify the points of minimum current and minimum voltage on an antenna?The various properties of a transmitting antenna can apply equally to the same antenna when it is used as a receiving antenna. What term is used for this property?The direction of what field is used to designate the polarization of a wave?If a wave's electric lines of force rotate through 360 degrees with every cycle of rf energy, what is the polarization of this wave?

ANSWERS:Half-wave (Hertz) and quarter-wave (Marconi).Coupling device, feeder, and antenna.Frequency of operation of the transmitter, amount of power to be radiated, and general direction of the receiving set.One-half the wavelength.Current and voltage loops.Current and voltage nodes.Reciprocity of antennas.Electric (E) field.Circular polarization.

What type of polarization should be used at medium and low frequencies?What is an advantage of using horizontal polarization at high frequencies?What type of polarization should be used if an antenna is mounted on a moving vehicle at frequencies below 50 megahertz?What is the radiation resistance of a half-wave antenna in free space?A radiating source that radiates energy stronger in one direction than another is known as what type of radiator?A radiating source that radiates energy equally in all directions is known as what type of radiator?A flashlight is an example of what type of radiator?What terms are often used to describe basic half-wave antennas?If a basic half-wave antenna is mounted vertically, what type of radiation pattern will be produced?In which plane will the half-wave antenna be operating if it is mounted horizontally?

ANSWERS: 10. Vertical polarization. 11. Less interference is experienced by man-made noise 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.

Since the radiation pattern of a dipole is similar to that of a doublet, what will happen to the pattern if the length of the doublet is increased?What is the simplest method of feeding power to the half-wave antenna?What is the radiation pattern of a quarter-wave antenna?Describe the physical arrangement of a ground screen.What is the difference in the amount of impedance between a three-wire dipole and a simple center-fed dipole?Which has a wider frequency range, a simple dipole or a folded dipole?

ANSWERS: 20. The pattern would flatten. 21. 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 2 feet 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 /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 short and long antenna4. 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 tie antenna ( = 35 o; 0.73); d) ground plane vertical.

QUESTIONS ??????

Wavelength vs Physical Length

The speed of a radio wave: is the same as the speed of lightThe velocity of propagation of radio frequency energy in free space is: 300 000 kilometers per secondIf an antenna is made longer, what happens to its resonant frequency? It decreasesIf an antenna is made shorter, what happens to its resonant frequency? It increasesThe resonant frequency of an antenna may be increased by: shortening the radiating element

Wavelength vs Physical Length

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

Wavelength vs Physical Length The wavelength for a frequency of 25 MHz is: 12 metres (39.4 ft) The wavelength corresponding to a frequency of 2 MHz is: 150 m (492 ft) At the end of suspended antenna wire, insulators are used. These act to: limit the electrical length of the antennaOne solution to multi-band operation with a shortened radiator is the "trap dipole" or trap vertical. These "traps" are actually: a coil and capacitor in parallel

Gain, Directivity

What is meant by antenna gain? The numerical ratio relating the radiated signal strength of an antenna to that of another antenna The gain of an antenna, especially on VHF and above, is quoted in dBi. The "i" in this expression stands for: Isotropic Approximately how much gain does a half-wave dipole have over an isotropic radiator? 2.1 dB What is a parasitic beam antenna? An antenna where some elements obtain their radio energy by induction or radiation from a driven element If a slightly shorter parasitic element is placed 0.1 wavelength away from an HF dipole antenna, what effect will this have on the antenna's radiation pattern? A major lobe will develop in the horizontal plane, toward the parasitic element 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 radiation pattern? A major lobe will develop in the horizontal plane, away from the parasitic element, toward the dipole

Gain, Directivity In free space, what is the radiation characteristic of a half-wave dipole? Minimum radiation from the ends, maximum broadside The front-to-back ratio of a beam antenna is: the ratio of the maximum forward power in the major lobe to the maximum backward power radiation The property of an antenna, which defines the range of frequencies to which it will respond, is called its: Bandwidth What is meant by antenna bandwidth? The frequency range over which the antenna may be expected to perform well How can the bandwidth of a parasitic beam antenna be increased? Use larger diameter elements

Vertical Antenna

To calculate the length in metres (feet) of a quarter wave vertical antenna you would : Divide 71.5 (234) by the antenna's operating frequency (in MHz)

If you made a quarter-wavelength vertical antenna for 21.125 MHz, how long would it be? 3.6 metres (11.8 ft)

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

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

What is an advantage of downward sloping radials on a ground plane antenna? It brings the feed point impedance closer to 50 ohms

Vertical AntennaWhat happens to the feed point impedance of a ground-plane antenna when its radials are changed from horizontal to downward-sloping? It increasesWhich of the following transmission lines will give the best match to the base of a quarter-wave ground-plane antenna? 50 ohms coaxial cableThe main characteristic of a vertical antenna is that it will: receive signals equally well from all compass points around itWhy is a loading coil often used with an HF mobile vertical antenna? To tune out capacitive reactanceWhat is the main reason why so many VHF base and mobile antennas are 5/8 of a wavelength? The angle of radiation is lowWhy is a 5/8-wavelength vertical antenna better than a 1/4-wavelength vertical antenna for VHF or UHF mobile operations? A 5/8-wavelength antenna has more gain

Yagi AntennaHow many directly driven elements do most Yagi antennas have? OneApproximately how long is the driven element of a Yagi antenna for 14.0 MHz? 10.21 metres (33 feet and 6 inches)Approximately how long is the director element of a Yagi antenna for 21.1 MHz? 6.4 metres (21 feet)Approximately how long is the reflector element of a Yagi antenna for 28.1 MHz? 5.33metres (17.5 feet long)The spacing between the elements on a three-element Yagi antenna, representing the best overall choice, is : 0.2 of a wavelength.What is one effect of increasing the boom length and adding directors to a Yagi antenna? Gain increasesWhat are some advantages of a Yagi with wide element spacing? High gain, less critical tuning and wider bandwidth

Wire Antenna

If you made a half-wavelength dipole antenna for 28.550 MHz, how long would it be? 5.08 metres (16.62 ft)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 antennaThe impedances in ohms at the feed point of the dipole and folded dipole are, respectively: 73 and 300

Wire AntennaA dipole transmitting antenna, placed so that the ends are pointing North/South, radiates: mostly to the East and WestHow does the bandwidth of a folded dipole antenna compare with that of a simple dipole antenna? It is greaterWhat is a disadvantage of using an antenna equipped with traps? It will radiate harmonicsWhat is an advantage of using a trap antenna? It may be used for multi- band operationWhat is one disadvantage of a random wire antenna? You may experience RF feedback in your station

Quad / Loop antenna

What is a cubical quad antenna? Two or more parallel four- sided wire loops, each approximately one-electrical wavelength longWhat is a delta loop antenna? A type of cubical quad antenna, except with triangular elements rather than squareThe cubical "quad" or "quad" antenna consists of two or more square loops of wire. The driven element has an approximate overall length of: one wavelengthThe delta loop antenna consists of two or more triangular structures mounted on a boom. The overall length of the driven element is approximately: one wavelengthApproximately how long is each side of a cubical quad antenna driven element for 21.4 MHz? 3.54 metres (11.7 feet)Approximately how long is each side of a cubical quad antenna driven element for 14.3 MHz? 5.36 metres (17.6 feet)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

Which statement about two- element delta loops and quad antennas is true? They compare favorably with a three element Yagi

Compared to a dipole antenna, what are the directional radiation characteristics of a cubical quad antenna? The quad has more directivity in both horizontal and vertical planes

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

What does the term "antenna front-to back ratio" mean in reference to a delta loop antenna? The power radiated in the major radiation lobe compared to the power radiated in exactly the opposite direction

EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*Warsaw Radio Mast, which was designed by Jan Polak, was 646.38metres (2,120.67ft) tall. Freq = 227 kHz. 2 MW transmitter, 120kV feed.EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*In the axial mode, the helix dimensions are at or above the wavelength of operation. The antenna then falls under the class of waveguide antennas, and produces true circular polarization. These antennas are best suited for animal tracking and space communication, where the orientation of the sender and receiver cannot be easily controlled, or where the polarization of the signal may change. Antenna size makes them unwieldy for low frequency operation, so they are commonly employed only at frequencies ranging from VHF up to microwave. EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*A log-periodic antenna (LP, also known as a log-periodic array) is a broadband, multi-element, unidirectional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency. The individual components are often dipoles, as in a log-periodic dipole array (LPDA). EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*The dipole in the array is driven, and another element, slightly longer, operates as a reflector. Other shorter parasitic elements are typically added in front of the dipole as directors. This arrangement gives the antenna directionality that a single dipole lacks. EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*he Horn Antenna, at Bell Telephone Laboratories in Holmdel, New Jersey, is listed as a National Historic Landmark because of its association with the research work of two radio astronomers, Arno Penzias and Robert Wilson.[1] In 1965 while using the Horn Antenna, Penzias and Wilson stumbled on the microwave background radiation that permeates the universe. Cosmologists quickly realized that Penzias and Wilson had made the most important discovery in modern astronomy since Edwin Hubble demonstrated in the 1920s that the universe was expanding. This discovery provided the evidence that confirmed George Gamow's and Abbe Georges Lemaitre's "Big Bang" theory of the creation of the universe and forever changed the science of cosmology the study of the history of the universe from a field for unlimited theoretical speculation into a subject disciplined by direct observation. In 1978 Penzias and Wilson received the Nobel Prize for Physics for their momentous discovery[4]. EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types*EEE381B Aerospace Systems & AvionicsAntenna Theory - Antenna types**