Antennas and Radiating Systems.pdf

7/27/2019 Antennas and Radiating Systems.pdf

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Radiation of electromagnetic waves


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Outline

z Introduction

zReview of basic antenna typeszRadiation pattern, gain, polarization

zEquivalent circuit & radiation efficiencyzSmart antennas

zSome theoryzSummary


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Antenna purpose

z Transformation of a guided EM

wave in transmission line(waveguide) into a freelypropagating EM wave in space (orvice versa) with specifieddirectional characteristics

{Transformation from time-function inone-dimensional space into time-

function in three dimensional space{The specific form of the radiated

wave is defined by the antennastructure and the environment

Space wave

Guided wave


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Antenna functions

zTransmission line{Power transport medium - must avoid power

reflections, otherwise use matching devices

zRadiator{Must radiate efficiently must be of a size

comparable with the half-wavelength

zResonator{Unavoidable - for broadband applications

resonances must be attenuated


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Monopole (dipole over plane)

Low-QBroadband

High-QNarrowband

z If there is an inhomogeneity (obstacle) a reflected wave, standing wave, & higher field modesappear

z With pure standing wave the energy is stored and oscillates from entirely electric to entirelymagnetic and back

z Model: a resonator with high Q = (energy stored) / (energy lost) per cycle, as in LC circuitsz Kraus p.2

Smooth

transitionregion

Uniform wave

travelingalong the line


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Outline

z Introduction





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Antennas for laptop applications

Source: D. Liu et al.: Developing integrated antenna subsystems for laptop computers; IBM J. RES. & DEV. VOL. 47 NO. 2/3 MARCH/MAY 2003 p. 355-367


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z Patch and slot antennasderived from printed-circuit andmicro-strip technologies

z Ceramic chip antennas aretypically helical or inverted-F(INF) antennas, or variations ofthese two types with high

dielectric loading to reduce theantenna size

Source: D. Liu et al.: Developing integrated antenna subsystems for laptopcomputers; IBM J. RES. & DEV. VOL. 47 NO. 2/3 MARCH/MAY 2003 p. 355-367


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Slot & INF antennasz Slot antenna: a slot is cut from a large (relative

to the slot length) metal plate.zThe center conductor of the feeding coaxial cable is

connected to one side of the slot, and the outsideconductor of the cable - to the other side of the slot.

z The slot length is some (/2) for the slot antennaand (/4) long for the INF antenna.

z The slot and INF antennas behave similarly.zThe slot antenna can be considered as a loaded version

of the INF antenna. The load is a quarter-wavelength stub,

i.e. a narrowband device.zWhen the feed point is moved to the short-circuited end ofthe slot (or INF) antenna, the impedance decreases.When it is moved to the slot center (or open end of theINF antenna), the impedance increases


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Exampledouble-layer printed Yagi antenna

Source: N Gregorieva

Note: no galvanic contact with thedirector


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zPatch and slot antennas are

{Cheap and easy to fabricate and to mount{Suited for integration

{Light and mechanically robust

{Have low cross-polarization

{Low-profile - widely used in antenna arrays

spacecrafts, satellites, missiles, cars and other mobileapplications


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Aperture-antenna

Note: The aperture concept is applicablealso to wired antennas. For instance,the max effective aperture of linear/2 wavelength dipole antenna is 2/8

EM wave

Powerabsorbed: P [watt]

Power density:PFD [w/m2]

Effectiveaperture: A[m2]

A = A*PFD

z Aperture antennasderived fromwaveguide technology(circular, rectangular)

z Can transfer high

power (magnetrons,klystrons)

z Above few GHz

z Will be exploredinprace during theschool


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Leaky-wave antennas

z Derived from millimeter-wave guides (dielectric

guides, microstrip lines,coplanar and slot lines).

z For frequencies > 30 GHz,

including infraredz Subject of intensive study.

{ Note: Periodicaldiscontinuities near the end

of the guide lead tosubstantial radiationleakage (radiation from thedielectric surface).

Source: adapted from N Gregorieva


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Reflector antennas

zReflectors are used to concentrate flux of EMenergy radiated/ received, or to change itsdirection

zUsually, they are parabolic (paraboloidal).{

The first parabolic (cylinder) reflector antenna was usedby Heinrich Hertz in 1888.

z Large reflectors have high gain and directivity{Are not easy to fabricate

{Are not mechanically robust

{Typical applications: radio telescopes, satellitetelecommunications.



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Planar reflectors

z Uda-Yagi, Log-periodic antennas

d

2d

z Intended reflector antennaallows maintaining radio link in

non-LOS conditions (avoidingpropagation obstacles)

z Unintended antennas createinterference


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Paraboloidal reflectors

Front feed Cassegrain feed


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The largest radio telescopes

Max Plank Institt fr Radioastronomie

radio telescope, Effelsberg (Germany),100-m paraboloidal reflector

zThe Green Bank Telescope (the NationalRadio Astronomy Observatory) paraboloid of aperture 100 m



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The Arecibo Observatory Antenna

SystemThe worldslargest single

radio telescope

304.8-msphericalreflector

NationalAstronomy andIonosphereCenter (USA),Arecibo,Puerto Rico


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The Arecibo Radio Telescope

[Sky & TelescopeFeb 1997 p. 29]


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Lens antennas

Source: Kraus p.382, N Gregorieva

Lenses play a similar role to that of reflectors in reflector antennas:they collimate divergent energyOften preferred to reflectors at frequencies > 100 GHz.


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Outline

z Introduction





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Radiation pattern

z The radiation pattern of antenna is a representation(pictorial or mathematical) of the distribution of the power

out-flowing (radiated) from the antenna (in the case oftransmitting antenna), or inflowing (received) to theantenna (in the case of receiving antenna) as a function

of direction angles from the antennazAntenna radiation pattern (antenna pattern):

is defined for large distances from the antenna, where the spatial(angular) distribution of the radiated power does not depend on the

distance from the radiation source is independent on the power flow direction: it is the same when the

antenna is used to transmit and when it is used to receive radio waves

is usually different for different frequencies and different polarizations

of radio wave radiated/ received


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Power pattern vs. Field pattern

z The power pattern is themeasured (calculated)

and plotted receivedpower: |P(, )| at aconstant (large) distancefrom the antenna

z The amplitude fieldpattern is the measured(calculated) and plottedelectric (magnetic) field

intensity, |E(

, )| or|H(, )| at a constant(large) distance from theantenna

Power orfield-strength meter

Antennaunder test

Turntable

Generator

Auxiliaryantenna

Large distance

z The power pattern and the field

patterns are inter-related:P(, ) = (1/)*|E(, )|2 = *|H(,)|2

P = power

E = electrical field component vector

H = magnetic field component vector

= 377 ohm (free-space, plane wave

impedance)


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Normalized pattern

zUsually, the pattern describes the

normalized field (power) values withrespect to the maximum value.

{Note: The power pattern and the amplitude fieldpattern are the same when computed and whenplotted in dB.


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3-D pattern

z Antenna radiation

pattern is3-dimensional

z The 3-D plot of antenna

pattern assumes bothangles and varying,which is difficult toproduce and to interpret

3-D pattern

Source: NK Nikolova


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2-D pattern

Two 2-D patterns

z Usually the antenna

pattern is presented as a2-D plot, with only one ofthe direction angles, or varies

zIt is an intersection of the3-D one with a given plane{ usually it is a = const

plane or a = const planethat contains the patternsmaximum

Source: NK Nikolova


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Example: a short dipole on z-axis

Source: NK Nikolova


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Principal patterns

z Principal patterns are the 2-D patterns

of linearly polarized antennas,measured in 2 planes

1. the E-plane: a plane parallel to the Evector and containing the direction ofmaximum radiation, and

2. the H-plane: a plane parallel to the Hvector, orthogonal to the E-plane, andcontaining the direction of maximum

radiation Source: NK Nikolova


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Example

Source: NK Nikolova


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Antenna Mask (Example 1)

Typical relative

directivity- maskof receivingantenna (Yagiant., TV dcmwaves)

[CCIR doc. 11/645, 17-Oct 1989)

-20

-15

-10

-5

0

-180

-120

-60 0

60

120

180

Azimi th angle, degrees

Relativegain,

dB


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Antenna Mask (Example 2)

-50

-40

-30

-20

-10

0

0.1 1 10 100

Phi/Phi0

Rela

tive

gain

(dB)

RR/1998 APS30 Fig.9

COPOLAR

CROSSPOLAR

Reference pattern for co-polar and cross-polar components forsatellite transmitting antennas in Regions 1 and 3 (Broadcasting

~12 GHz)

0dB

-3dBPhi


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Isotropic antenna

z Isotropic antenna orisotropic radiatoris a

hypothetical (not physicallyrealizable) concept, used as auseful reference to describe

real antennas.z Isotropic antenna radiatesequally in all directions.{Its radiation pattern is

represented by a sphere whosecenter coincides with the locationof the isotropic radiator.

Source: NK Nikolova


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Directional antenna

zDirectional antenna is an antenna, which

radiates (or receives) much more power in(or from) some directions than in (or from)others.

{Note: Usually, this term is applied to antennaswhose directivity is much higher than that of a

half-wavelength dipole.

Source: NK Nikolova


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Omnidirectional antenna

zAn antenna, which

has a non-directional patternin a plane

{It is usuallydirectional in other

planes

Source: NK Nikolova


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Pattern lobes

Source: NK Nikolova

Pattern lobe is a

portion of the radiationpattern with a localmaximum

Lobes are classifiedas: major, minor,side lobes, backlobes.


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Pattern lobes and beam widths

Source: NK Nikolova


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Beamwidth

zHalf-power beamwidth (HPBW) is the anglebetween two vectors from the patterns origin tothe points of the major lobe where the radiationintensity is half its maximum

zOften used to describe the antenna resolution properties

y Important in radar technology, radioastronomy, etc.

z First-null beamwidth (FNBW) is the angle

between two vectors, originating at the patternsorigin and tangent to the main beam at its base.y Often FNBW 2*HPBW


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Example

Source: NK Nikolova


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Anisotropic sources: gain

z Every real antenna radiates moreenergy in some directions than inothers (i.e. has directional properties)

z Idealized example of directionalantenna: the radiated energy isconcentrated in the yellow region(cone).

z Directive antenna gain: the power fluxdensity is increased by (roughly) theinverse ratio of the yellow area and thetotal surface of the isotropic sphere

{ Gain in the field intensity may also beconsidered - it is equal to the squareroot of the power gain.

Isotropic sphere


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Antenna gain measurement

Antenna Gain = (P/Po) S=S0

Actualantenna

P = Powerdelivered tothe actualantenna

S = Powerreceived

(the same inboth steps)

Measuringequipment

Step 2: substitution

Referenceantenna

Po = Powerdelivered tothe reference

antenna

S0 = Powerreceived

(the same inboth steps)

Measuringequipment

Step 1: reference


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Antenna Gains Gi, Gd

zUnless otherwise specified, the gain refers

to the direction of maximum radiation.zGain is a dimension-less factor related to

power and usually expressed in decibels

zGi Isotropic Power Gain theoreticalconcept, the reference antenna is isotropic

zGd - the reference antenna is a half-wavedipole

T i l G i d B idth


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Typical Gain and Beamwidth

Type of antenna Gi [dB] BeamW.

Isotropic 0 3600x3600

Half-wave Dipole 2 360

0

x1200

Helix (10 turn) 14 350x350

Small dish 16 300x300

Large dish 45 10x10

A t i d ff ti


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Antenna gain and effective area

zMeasure of the effective absorption areapresented by an antenna to an incident planewave.

zDepends on the antenna gain and wavelength2 2( , ) [m ]4

eA G

=

Aperture efficiency: a = Ae / AA: physical area of antennas aperture, square meters

P T f i F S


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Power Transfer in Free Space

z : wavelength [m]

z PR: power available at the

receiving antennaz PT: power delivered to the

transmitting antenna

z GR: gain of the transmitting

antenna in the direction ofthe receiving antenna

z GT: gain of the receivingantenna in the direction ofthe transmitting antenna

z Matched polarizations

2

2

2

4

44

=

=

=

rGGP

G

r

PG

APFDP

RTT

RTT

eR

i


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e.i.r.p.

zEquivalent Isotropically Radiated

Power (in a given direction):

zThe product of the power supplied to the

antenna and the antenna gain (relativeto an isotropic antenna) in a givendirection

. . . . ie i r p PG=

Li P l i ti


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Linear Polarization

z In a linearly polarizedplane wave the directionof the E (or H) vector is

constant.

z http://www.amanogawa.com/archive/wavesA.h

tml

Elliptical Polari ation
http://www.amanogawa.com/archive/wavesA.htmlhttp://www.amanogawa.com/archive/wavesA.htmlhttp://www.amanogawa.com/archive/wavesA.htmlhttp://www.amanogawa.com/archive/wavesA.html


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Elliptical Polarization

Ex = cos (wt)

Ey = cos (wt)

Ex = cos (wt)

Ey = cos (wt+pi/4)Ex = cos (wt)

Ey = -sin (wt)

Ex = cos (wt)

Ey = cos (wt+3pi/4)

Ex = cos (wt)

Ey = -cos (wt+pi/4)

Ex = cos (wt)

Ey = sin (wt)

LHC

RHC

Polarization ellipse


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Polarization ellipse

z The superposition oftwo plane-wave

components results inan ellipticallypolarized wave

z The polarizationellipse is defined byits axial ratio N/M

(ellipticity), tilt angle and sense of rotation

Ey

Ex

M

N

Polarization states


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Polarization states

450 LINEAR

UPPER HEMISPHERE:

ELLIPTIC POLARIZATIONLEFT_HANDED SENSE

LOWER HEMISPHERE:ELLIPTIC POLARIZATION

RIGHT_HANDED SENSE

EQUATOR:

LINEAR POLARIZATION

LATTITUDE:REPRESENTSAXIAL RATIO

LONGITUDE:REPRESENTSTILT ANGLE

POLES REPRESENTCIRCULAR POLARIZATIONS

LHC

RHC

(Poincar sphere)

Comments on Polarization


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Comments on Polarization

zAt any moment in a chosen reference point inspace, there is actually a single electric vector E(and associated magnetic vector H).

z This is the result of superposition (addition) of

the instantaneous fields E (and H) produced byall radiation sources active at the moment.

z The separation of fields by their wavelength,

polarization, or direction is the result of filtration.

Antenna Polarization


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Antenna Polarization

z The polarization of an antenna in a specificdirection is defined to be the polarization of thewave produced by the antenna at a great

distance at this direction

Polarization Efficiency


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Polarization Efficiency

z The power received by an antenna

from a particular direction is maximal if thepolarization of the incident wave and thepolarization of the antenna in the wave arrivaldirection have:{ the same axial ratio

{the same sense of polarization

{ the same spatial orientation

.


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Power transfer


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Power transfer

zThe maximumpower is deliveredto (or from) theantenna when the

antennaimpedance and theimpedance of the

equivalentgenerator (or load)are matched

0

0.5

1

0.1 1 10

RA / RG; (XA+XG = 0)

P

A

/PAmax


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zWhen the antenna impedance is not matched tothe transmitter output impedance (or to the

receiver input impedance) or to the transmissionline between them, impedance-matchingdevices must be used for maximum power

transferz Inexpensive impedance-matching devices are

usually narrow-band

z Transmission lines often have significant losses


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Antenna arrays


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y

z Consist of multiple (usually identical) antennas (elements)collaborating to synthesize radiation characteristics notavailable with a single antenna. They are able{ to match the radiation pattern to the desired coverage area{ to change the radiation pattern electronically (electronic

scanning) through the control of the phase and the amplitude ofthe signal fed to each element

{ to adapt to changing signal conditions{ to increase transmission capacity by better use of the radio

resources and reducing interference

z Complex & costly Intensive research related to military, space, etc. activities

y Smart antennas, signal-processing antennas, tracking antennas,phased arrays, etc.


Satellite antennas (TV)


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( )

zNot an array!

Owens Valley Radio Observatory


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y y

The Earthsatmosphere istransparent in

the narrowvisible-lightwindow(4000-7000angstroms) and

the radio bandbetween 1 mmand 10 m.

[Sky & Telescope

Feb 1997 p.26]


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The New Mexico Very Large Array

27 antennas along 3 railroad tracks provide baselines up to 35 km.

Radio images are formed by correlating the signals garnered byeach antenna.

[Sky & TelescopeFeb 1997 p. 30]

2 GHz adaptive antenna


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p

zA set of 48

2GHzantennas{ Source:

Arraycomm

Phased Arrays


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y

zArray of N antennas in a linear or two-dimensional configuration + beam-forming

& control devicez The amplitude and phase excitation of each

individual antenna controlled electronically

(software-defined){Diode phase shifters

{Ferrite phase shifters

z Inertia-less beam-forming and scanning (sec)with fixed physical structure


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zDynamically phased array

(PA):{A generalization of the

switched lobe concept

{The radiation patterncontinuously track thedesignated signal (user)

{Include a direction of arrival(DoA) tracking algorithm


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Switched-Line Phase Bit


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Phase bit = delay difference

Input Output

Diode switch

Delay line #1a

Delay line #1b

Simulation


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z 2 omnidirectional antennas (equal amplitudes)

{Variableszdistance increment

zphase increment

zN omnidirectional antennas{Group factor (N omnidirectional antennas uniformly

distributed along a straight line, equal amplitudes, equalphase increment)

z http://www.amanogawa.com/archive/TwoDipole/Antenna2-2.html (more details)

2 omnidirectional antennas
http://array2ant.xls/http://array_nant.xls/http://www.amanogawa.com/archive/TwoDipole/Antenna2-2.htmlhttp://www.amanogawa.com/archive/TwoDipole/Antenna2-2.htmlhttp://www.amanogawa.com/archive/TwoDipole/Antenna2-2.htmlhttp://www.amanogawa.com/archive/TwoDipole/Antenna2-2.htmlhttp://array_nant.xls/http://array2ant.xls/


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-1

-0.5

0

0.5

1

-1 -0.5 0 0.5 1

D = 0.5, = 900-1

-0.5

0

0.5

1

-1 -0.5 0 0.5 1

-1

-0.5

0

0.5

1

-1 -0.5 0 0.5 1

D = 0.5, = 00 D = 0.5, = 1800


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Adaptive (Intelligent)Antennas


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z Array of N antennas in a linear,circular, or planar configuration

z Used for selection signals from

desired sources and suppressincident signals from undesiredsources

z The antenna pattern track the

sourcesz It is then adjusted to null out the

interferers and to maximize thesignal to interference ratio (SIR)

z Able to receive and combineconstructively multipath signals


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EM Field of Current Element

HHHH

EEEE

r

r

GGGG

GGGK

++=

++=

I: current (monochromatic) [A]; dz: antenna element (short) [m]x

y

z

OP

r

ErE

E

I, dz222

222

HHHH

EEEE

r

r

++=

++=


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Linear Antennas


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z Summation of all vectorcomponents E (or H)produced by each antenna

element

z In the far-field region,the vector componentsare parallel to each other

z Phase difference due to{ Excitation phase difference{ Path distance difference

z Method of moments

...

...

321

321

+++=

+++=

HHHH

EEEEGGGG

GGGK

O


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Antenna Bandwidth


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Zeland Software, Inc. & BAY TECHNOLOGY,

IE3D Benchmark Simulation Example


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Far Field Expression


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hI

R

ejkE

jkR

4~

R

Vg

ERH

~

Antenna Pattern 3D


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Antenna Simulation


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Zeland Software, Inc. & BAY TECHNOLOGY, IE3D Benchmark Simulation Example


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Equivalent Circuit ofReceiving Antenna


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Voc

Z A

Z LZo

hEVi

oc =


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Effective Area of aReceiving Antenna


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D

AA

e

e

i

A

i

A

i

r

GR

h

R

hA

AE

R

hE

R

hEP

444

2428

2

2

22

2

22222

=

==

=

==


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Input Impedance


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,,, 1992


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Image Theory forElectric Currents


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Image Theory forMagnetic Currents


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Microstrip Traveling-Wave Antennas


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,,, 1992


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Microstrip Antenna Array Element


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,,, 1992


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Antenna Array


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Antennas and Radiating Systems.pdf

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