5anten_theor_bascs

8/2/2019 5Anten_theor_bascs

1/60

Basic Antenna Theory

Ryszard Struzakwww. ryszard.struzak.com

Note: These are preliminary notes, intended only fordistribution among the participants. Beware of misprints!

ICTP-ITU-URSI School on Wireless Networking for DevelopmentThe Abdus Salam International Centre for Theoretical Physics ICTP, Trieste (Italy), 6 to 24 February 2006

Property of R Struzak 2

Purpose

to refresh basic concepts related to theantenna physics needed to understand better the operation

and design of microwave links and networks


2/60


Outline

Introduction

Review of basic antenna types

Radiation pattern, gain, polarization

Equivalent circuit & radiation efficiency

Smart antennas

Some theory

Summary


Quiz

Transmitting antennas are used to radiateenergy in the form of radio waves

Receiving antennas -- to capture that energy

Somebody told that the receiving antennaduring the reception also radiates radio

wavesIs it a true fact or a slip of the tongue?


3/60


Intended & unintended radiators Intended antennas

To produce/ receive specified EM waves: Radiocommunicationantennas; Measuring antennas; EM sensors, probes; EM applicators(Industrial, Medical, Scientific)

Unintended antennas - active EM waves radiated as an unintended side-effect:

Any conductor/ installation with varying electrical current (e.g. electricalinstallation of vehicles)

Any slot/ opening in the screen of a device/ cable carrying RF current

Any discontinuity in transmission medium (e.g. conducting structures/installations) irradiated by EM waves

Unintended antennas - passive Stationary (e.g. antenna masts or power line wires); Time-varying (e.g.windmill or helicopter propellers); Transient (e.g. aeroplanes, missiles)


Antenna fuction

Transformation of a guided EMwave (in waveguide/ transmissionline ) into an EM wave freelypropagating in space, withspecified directional characteristics(or vice versa)

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

function in three dimensional space

The specific form of the radiated waveis defined by the antenna structure

and the environment

Space wave

Guided wave


4/60


Transmission line

Power transport medium - must avoid powerreflections, otherwise use matching devices

Radiator

Must radiate efficiently must be of a sizecomparable with the half-wavelength

Resonator

Unavoidable - for broadband applicationsresonances must be attenuated


Monopole (dipole over plane)

Low-Q

Broadband

High-Q

Narrowband

If there is an inhomogeneity (obstacle, or sharp transition), higher field-modes,reflections, and standing wave appear.

With standing wave, the energy is stored in, and oscillates from electric energy tomagnetic one and back. This can be modeled as a resonating LC circuit withQ = (energy stored per cycle) / (energy lost per cycle)

Kraus p.2

Smooth

transition

region

Uniform wave

traveling

along the line

Thick radiatorThin radiator

Sharp

transition

region


5/60


Outline

Introduction




Smart antennas

Some theory

Summary


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


6/60


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

Ceramic chip antennas aretypically helical or inverted-F(INF) antennas, or variations ofthese two types with highdielectric loading to reduce the

antenna 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


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

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

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

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

The slot and INF antennas behave similarly. The 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. When the feed point is moved to the short-circuited end of

the slot (or INF) antenna, the impedance decreases. When itis moved to the slot center (or open end of the INF antenna),the impedance increases


7/60


Exampledouble-layer printed Yagi antenna

Source: N Gregorieva

Note: no galvanic contact with thedirector


Patch 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 mobile

applications


8/60


Aperture-antenna

EM wave

Power

absorbed: P [watt]

Power density:

PFD [w/m2]

Effective

aperture: A[m2]

A = A*PFD

Aperture antennasderived fromwaveguide technology(circular, rectangular)

Can transfer highpower (magnetrons,klystrons)

Above few GHz

Will be explored inpractice during the

school Note: The aperture concept is applicable also to wired

antennas. For instance, the max effective aperture oflinear /2 wavelength dipole antenna is 2/8


Leaky-wave antennas Derived from millimeter-

wave guides (dielectricguides, microstrip lines,coplanar and slot lines).

For frequencies > 30 GHz,including infrared

Subject of intensive study. Note: Periodical

discontinuities near the endof the guide lead tosubstantial radiationleakage (radiation from thedielectric surface).

Source: adapted from N Gregorieva


9/60


Reflector antennas

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

Usually, they are parabolic (paraboloidal). The first parabolic (cylinder) reflector antenna was

used by Heinrich Hertz in 1888.

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

Are not mechanically robust

Typical applications: radio telescopes, satellitetelecommunications.



Planar reflectors

Uda-Yagi, Log-periodic antennas

d

2d

Intended reflector antennaallows maintaining radio link innon-LOS conditions (avoiding

propagation obstacles)

Unintended reflector antennascreate interference


10/60


Image Theory Antenna above perfectly

conducting plane surface

Tangential electrical fieldcomponent = 0 vertical components: the

same direction

horizontal components:opposite directions

The field (above the ground)is the same as if the groundis replaced by an mirror

image of the antenna http://www.amanogawa.com/

archive/wavesA.html

+

-

Elliptical polarization:

change of the rotation sense!


Paraboloidal reflectors

Front feed Cassegrain feed


11/60


The largest radio telescopes

Max Plank Institt fr Radioastronomieradio telescope, Effelsberg (Germany),100-m paraboloidal reflector

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



The Arecibo Observatory AntennaSystemThe worldslargest single

radio telescope

304.8-m

sphericalreflector

National

Astronomy andIonosphere

Center (USA),Arecibo,

Puerto Rico


12/60


The Arecibo Radio Telescope

[Sky & TelescopeFeb 1997 p. 29]


Lens antennas

Source: Kraus p.382, N Gregorieva

Lenses play a similar role to that of reflectors in reflector antennas:

they collimate divergent energy

Often preferred to reflectors at frequencies > 100 GHz.


13/60


14/60


Radiation pattern

The radiation pattern of antennais a representation(pictorial or mathematical) of the distribution of the powerout-flowing (radiated) from the antenna (in the case oftransmitting antenna), or inflowing (received) to theantenna (in the case of receiving antenna) as a functionof direction angles from the antenna

Antenna 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 thedistance 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


Power pattern vs. Field pattern The power patternis the

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

The amplitude fieldpatternis the measured(calculated) and plottedelectric (magnetic) fieldintensity, |E(, )| or|H(, )| at a constant(large) distance from theantenna

Power- orfield-strength meter

AUT

Antennaunder test

Turntable

Generator

Auxiliaryantenna

Largedistance

The power pattern and the field patternsare inter-related for plane wave:P(, ) = (1/)*|E(, )|2 = *|H(, )|2

P = power

E = electrical field component vector

H = magnetic field component vector

= 377 ohm (free-space, plane waveimpedance)


15/60


Normalized pattern

Usually, the pattern describes thenormalizedfield (power) values withrespect to the maximum value.

Note: The power pattern and the amplitudefield pattern are the same when computedand when plotted in dB.


Reference antenna (/2 dipole)


16/60


Reference antenna (/2 dipole)



17/60


Biquad antenna


Biquad


18/60


Cantenna


Cantenna


19/60


3-D pattern

Antenna radiationpattern is3-dimensional

The 3-D plot of antennapattern assumes bothangles and varying,which is difficult toproduce and to interpret

3-D pattern

Source: NK Nikolova


2-D pattern

Two 2-D patterns

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

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

plane or a = constplane

that contains the patternsmaximum

Source: NK Nikolova


20/60


21/602


Example

Source: NK Nikolova


Isotropic antenna Isotropic antenna or

isotropic radiatoris ahypothetical (not physicallyrealizable) concept, used as auseful reference to describereal antennas.

Isotropic antenna radiatesequally in all directions.

Its radiation pattern isrepresented by a sphere whosecenter coincides with thelocation of the isotropic radiator.

Source: NK Nikolova


22/602


Directional antenna

Directional antennais an antenna, whichradiates (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 ahalf-wavelength dipole.

Source: NK Nikolova


Omnidirectional antenna

An antenna, whichhas a non-directional patternin a plane

It is usuallydirectional in other

planes

Source: NK Nikolova


23/602


Pattern lobes

Source: NK Nikolova

Pattern lobe is a

portion of the radiation

pattern with a local

maximum

Lobes are classified

as: major, minor,

side lobes, back

lobes.


Pattern lobes and beam widths

Source: NK Nikolova


24/602


Example

Source: NK Nikolova


Beamwidth

Half-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

Often used to describe the antenna resolution properties

Important in radar technology, radioastronomy, etc.

First-null beamwidth(FNBW) is the angle

between two vectors, originating at the patternsorigin and tangent to the main beam at its base.

Often FNBW 2*HPBW


25/602


Antenna Mask (Example 1)

Typical relativedirectivity- maskof receivingantenna (Yagiant., TV dcmwaves)

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

-20

-15

-10

-5

0

-180

-120

-6 0 0

60

120

180

Azimith angle, degree s

Relativegain,

dB


Antenna Mask (Example 2)

-50

-40

-30

-20

-10

0

0.1 1 10 100

Phi/Phi0

Relative

gain

(dB)

RR/1998 APS30 Fig.9

COPOLAR

CROSSPOLAR

Reference pattern for co-polar and cross-polar components for

satellite transmitting antennas in Regions 1 and 3 (Broadcasting

~12 GHz)

0dB

-3dBPhi


26/602


Equivalent half-power beamwidth representationsof an antennas radiation pattern.

Volts


Anisotropic sources: gain Every real antenna radiates more

energy in some directions than inothers (i.e. has directional properties)

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

Directive antenna gain: the power fluxdensity is increased by (roughly) theinverse ratio of the yellow area and the

total surface of the isotropic sphere Gain in the field intensity may also be

considered - it is equal to the squareroot of the power gain.

Hypothetic

isotropic

antenna

Hypothetic

directional

antenna


27/602


Plane angle: radian

Angle in radians, = l/ r; l = *r

l is the length of the arcsegment supported by theangle in a circle of radius r.

There are 2 rad in a fullcircle

1 rad = (360 / 2) deg

l

r


Solid angle: steradian Solid angle in steradians (sr),

= (S)/r2; S= r

2

S is the spherical surface area supportedby the solid angle in a sphere of radius r

The steradian is the area cut out by the solidangle, divided by the spheres radiussquared - squared radian.

If the area is S, and the radius is d, then theangle is S/d2 steradians. The total solidangle (a full sphere) is thus 4 steradians.

As one radian is 180/ = 57.3 degrees, thetotal solid angle is 4 x (57.3)2 41253square degrees, one steradian is 3282.806square degrees, and one square degree isabout 305 x 10-6 steradians


28/602


Example: gain of 1 deg2 antenna

A hypothetical source radiates Pwatts uniformly within the solid angleof steradians in a given directionand zero outside

The total surface of the sphere is4d2 and the average irradiance isthe power divided by the surface:[P/(4d2)] w/m2

steradians corresponds tospherical surface of d2 andirradiance within that angle is[P/d2] w/m2

The antenna gain equals the ratio ofthese two, or 4/

For = 1 deg2 (= 305*10-6 sr); the

gain = 4/305*10-6

= 46 dB. ,

srP/d2

P/(4d2)

G =4/

If = 1 deg2, then

G = 4/305*10-6 = 46 dB


Effect of sidelobesLet the main beamwidth of an antenna be square degrees, with uniform irradiance ofW watts per square meter. Let the sidelobe irradiance (outside the main beam) beuniform and k times weaker, i.e. (W/k) watts per square meter, k 1. Then:

The gain decreases with the sidelobe level

and beamwidth.

If the main lobe is 1 square degree and the

sidelobes are attenuated by 20 dB,

then k =100 and G = 100 (or 20dB) ,

much less than in the previous example

(46dB).

In the limit, when k = 1, the gain tends to1 and antenna becomes isotropic.

.

0

1

1 1

41253

WG

kW

k k

= =

+

W

W/k


29/602


( )

2

2

2

0 2

- power radiated within the main lobe

41253 - power radiated by sidelobes

41253- total power

1- avera

41253 41253

M

S

T M S

T

P W d

WP d

k

P P P Wd k k

P kW W

d k k

=

=

= + = +

= = +

0

ge irradiation

1- antenna gain

1 1

41253

WG

kW

k k

= =

+

.


Antenna gain measurement

Antenna Gain = (P/Po) S=S0

Actual

antenna

P = Power

delivered to

the actual

antenna

S = Power

received

(the same in

both steps)

Measuring

equipment

Step 2: substitution

Reference

antenna

Po = Power

delivered to

the reference

antenna

S0 = Power

received

(the same in

both steps)

Measuring

equipment

Step 1: reference


30/60


31/603


Gain, Directivity, Radiation

Efficiency

The radiation intensity,directivity and gain aremeasures of the ability of anantenna to concentratepower in a particulardirection.

Directivity relates to thepower radiated by antenna(P0 )

Gain relates to the powerdelivered to antenna (PT)

: radiation efficiency(0.5 - 0.75)

0

),(),(

P

P

DG

T=

=


Antenna gain and effective area

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

Depends on the antenna gain and wavelength2

2( , ) [m ]4

eA G

=

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


32/603


Power Transfer in Free Space

: wavelength [m]

PR: power available at the

receiving antenna

PT: power delivered to thetransmitting antenna

GR: gain of the transmitting

antenna in the direction ofthe receiving antenna

GT: gain of the receiving

antenna in the direction ofthe transmitting antenna

Matched polarizations

2

2

2

4

44

=

=

=

r

GGP

G

r

PG

APFDP

RTT

RTT

eR


e.i.r.p.

Equivalent Isotropically Radiated

Power (in a given direction):

The product of the power supplied to the

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

. . . . ie i r p PG=


33/603


Linear Polarization

In a linearly polarizedplane wave the directionof the E (or H) vector isconstant.


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


34/603


Polarization ellipse

The superposition oftwo plane-wavecomponents results inan ellipticallypolarized wave

The polarizationellipse is defined byits axial ratio N/M(ellipticity), tilt angle

and sense of rotation

Ey

Ex

M

N


Polarization states

450 LINEAR

UPPER HEMISPHERE:ELLIPTIC POLARIZATIONLEFT_HANDED SENSE

LOWER HEMISPHERE:

ELLIPTIC POLARIZATIONRIGHT_HANDED SENSE

EQUATOR:LINEAR POLARIZATION

LATTITUDE:REPRESENTSAXIAL RATIO

LONGITUDE:REPRESENTSTILT ANGLE

POLES REPRESENTCIRCULAR POLARIZATIONS

LHC

RHC

(Poincar sphere)


35/603


Comments on Polarization

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

This is the result of superposition (addition) ofthe instantaneous fields E (and H) produced byall radiation sources active at the moment.

The separation of fields by their wavelength,polarization, or direction is the result of filtration.


Antenna Polarization

The polarization of an antenna in a specificdirection is defined to be the polarization of thewave produced by the antenna at a greatdistance at this direction


36/603


Polarization Efficiency

The power received by an antennafrom a particular direction is maximal if thepolarization of the incident wave and the

polarization of the antenna in the wave arrivaldirection have:

the same axial ratio

the same sense of polarization

the same spatial orientation.


Polarization filters/ reflectors

At the surface of ideal conductor the tangential

electrical field component = 0

|E1|>0 |E2| = 0

Vector E wiresVector E || wires

|E1|>0 |E2| ~ |E2|

Wall of thin parallel wires (conductors)

Wire distance ~ 0.1


37/603


Outline

Introduction




Smart antennas

Some theory

Summary


Transmitting antenna equivalent circuit

Transmitter Transm. line

Antenna

G

enerator

RG

jXG

VG

jXA

Rr

Rl

The transmitter with the transmission line isrepresented by an (Thevenin) equivalent generator

The antenna is represented by its input impedance(which is frequency-dependent and is influenced byobjects nearby) as seem from the generator

jXA represents energy stored in electric (Ee) andmagnetic (Em) near-field components; if |Ee| = |Em|then XA = 0 (antenna resonance)

Rr represents energy radiated into space (far-fieldcomponents)

Rlrepresents energy lost, i.e. transformed into heat inthe antenna structure

Radio wave


38/603


Power transfer: Tx antenna

Generator

RG

jXG

VG

jXA

RR

RL

( ) ( )

( ) ( )

2

2

2

2 2

2

2 2

2

Transmitter is represented by an eqivalent

generator with , , .

Let ; , var.

The power absorbed by antenna

G G G

A R L A A

A

G

G A G A

AG

G A G A

G

G

V R X const

R R R R X

P I R

VI

R R X X

RP V

R R X X

VP

R

=

= + =

=

= + + +

=+ + +

=

2 2

1

A

G

GA A

G G G

R

R

XR X

R R R

+ + +


( )

( )

( ) ( )

2

2 2 2

2

22 2

2

2 2

0, when

AG

G A G G A A

A G A

G

AG A G A

A G

A

RP V

R R X X X X

R X X PV

X R R X X

PX X

X

=+ + + +

+

= + + +

= =

( )

( ) ( )

( )

( )

2

2

2

2

22

2 2 22

22

Let 0. Then

2

2 2 2

0, when

AG A G

G A

G A A G A

G

AG A

G G A A G A AG

G A

G A

A

R X X P V

R R

R R R R RPV

R R R

R R R R R R RV

R R

PR R

R

+ = =+

+ +

= = +

+ +

= +

= =

2

: 0

,

4

A A

A G A G

G

G

P PMaximum

R X

R R X X

VP

R

+ =

= =

=


39/603


Impedance matching

( )

( )

( )

2

2

4

4

A r l g

A g

g

A

A

g

g A

g

rr A

r l

l

l A

r l

R R R R

X X

VP

R

VP P

R

RP P

R R

RP PR R

= + =

=

=

= =

=+

=+


Power vs. field strength2

0

0

2 2

0

0 377 ohms

for plane wave

in free space

r r

EP E P Z

Z

E E E

EH

Z

Z

= =

= +

=

=


40/604


Receiving antenna equivalent circuit

AntennaRr

jXA

VA

jXL

RLRl

Thevenin equivalent

The antenna with the transmission line isrepresented by an (Thevenin) equivalentgenerator

The receiver is represented by its inputimpedance as seen from the antenna terminals(i.e. transformed by the transmission line)

VA is the (induced by the incident wave) voltageat the antenna terminals determined when theantenna is open circuited

Note: The antenna impedance is the same when the antenna isused to radiate and when it is used to receive energy

Radio wave ReceiverTransm.line

Antenna


Power transfer

The maximumpower is deliveredto (or from) theantenna when theantennaimpedance and theimpedance of theequivalentgenerator (or load)are matched

0

0.5

1

0.1 1 10

RA / RG; (XA+XG = 0)

PA/PAmax


41/604


When the impedances are matched

Half of the source power is delivered to the load andhalf is dissipated within the (equivalent) generator asheat

In the case of receiving antenna, a part (Pl) of thepower captured is lost as heat in the antennaelements, , the other part being reradiated (scattered)back into space

Even when the antenna losses tend to zero, still only half of

the power captured is delivered to the load (in the case ofconjugate matching), the other half being scattered back intospace


When the antenna impedance is not matched tothe transmitter output impedance (or to thereceiver input impedance) or to the transmissionline between them, impedance-matchingdevices must be used for maximum powertransfer

Inexpensive impedance-matching devices are

usually narrow-band Transmission lines often have significant losses


42/604


Radiation efficiency

The radiation efficiency eindicates howefficiently the antenna uses the RF power

It is the ratio of the power radiated by theantenna and the total power delivered tothe antenna terminals (in transmittingmode). In terms of equivalent circuitparameters:

r

r l

ReR R

=+


Outline

Introduction




Smart antennas

Some theory

Summary


43/604


Antenna arrays

Consist of multiple (usually identical) antennas(elements) collaborating to synthesize radiationcharacteristics not available with a single antenna. Theyare able to match the radiation pattern to the desired coverage area

to change the radiation pattern electronically (electronicscanning) 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

Complex & costly

Intensive research related to military, space, etc. activities Smart antennas, signal-processing antennas, tracking antennas,

phased arrays, etc.



Satellite antennas (TV)

Not an array!


44/604


Owens Valley Radio

Observatory The Earthsatmosphere istransparent inthe narrowvisible-lightwindow(4000-7000angstroms) andthe radio bandbetween 1 mmand 10 m.

[Sky & TelescopeFeb 1997 p.26]


The New Mexico Very LargeArray

27 antennas along 3 railroad tracks provide baselines up to 35 km.Radio images are formed by correlating the signals garnered byeach antenna.

[Sky & Telescope

Feb 1997 p. 30]


45/60


46/604


Switched beam antennas Based on switching function between

separate directive antennas orpredefined beams of an array

Space Division Multiple Access(SDMA) = allocating an angledirection sector to each user In a TDMA system, two users will be

allocated to the same time slot andthe same carrier frequency

They will be differentiated by differentdirection angles


Dynamically phased array(PA):

A generalization of theswitched lobe concept

The radiation pattern

continuously track the

designated signal (user) Include a direction of arrival

(DoA) tracking algorithm


47/604


Beam Steering

Beam-steeringusingphaseshifters ateachradiatingelement

Radiating

elements

Power

distribution

Phase

shifters

Equi-phase

wave front

= [(2/)d sin]

3 2 0

d

Beam direction


4-Bit Phase-Shifter (Example)

Alternative solution: Transmission line with controlled delay

00 or22.50 00 or450 00 or900 00 or1800Input Output

Bit #4 Bit #3 Bit #2 Bit #1

Steering/ Beam-forming Circuitry


48/604


Switched-Line Phase Bit

Phase bit = delay difference

Input Output

Diode switch

Delay line #1a

Delay line #1b


Simulation

2 omnidirectional antennas (equalamplitudes) Variables

distance increment

phase increment

N omnidirectional antennas Group factor (N omnidirectional antennas

uniformly distributed along a straight line,equal amplitudes, equal phase increment)


49/604


2 omnidirectional antennas

-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


N omnidirectional antennas

Array gain (line, uniform, identical power)

0

0.5

1

1.5

2

2.5

-180 -90 0 90 180

Azimuth angle, degrees

Relativegain

N = 2, = 900 N = 9, = 450N = 5, = 1800

0

1

2

3

4

5

6

-180 -90 0 90 180


Relativegain

0

1

2

3

4

5

6

7

8

9

10

-180 -90 0 90 180


Relativegain


50/60


51/605


The amplitude/ phase

excitation of eachantenna controlledelectronically(software-defined)

The weight-determiningalgorithm uses a-prioriand/ or measuredinformation to adaptantenna to changingenvironment

The weight andsumming circuits canoperate at the RF and/or at an intermediatefrequency

w1

wN

Weight-determining

algorithm

1

N


Antenna sitting

Radio horizon

Effects of obstacles & structures nearby

Safety

operating procedures

Grounding

lightning strikes

static charges

Surge protection

lightning searches for a second path to ground


52/605


Outline

Introduction




Smart antennas

Some theory

Summary


Maxwells Equations EM field interacting with the matter

2 coupled vectors E and H (6 numbers!), varying with time andspace and satisfying the boundary conditions(see http://www.amanogawa.com/archive/docs/EM1.pdf;http://www.amanogawa.com/archive/docs/EM7.pdf;http://www.amanogawa.com/archive/docs/EM5.pdf)

Reciprocity Theorem Antenna characteristics do not depend on the direction of energy

flow. The impedance & radiation pattern are the same when theantenna radiates signal and when it receives it.

Note: This theorem is valid only for linear passive antennas (i.e.antennas that do not contain nonlinear and unilateral elements,e.g. amplifiers)


53/605


EM Field of Current Element

HHHH

EEEE

r

r

rrrr

rrrv

++=

++=

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

y

z

OP

r

ErE

E

I, dz222

222

HHHH

EEEE

r

r

++=

++=


Short dipole antenna: summary E & H are maximal in the equatorial plane, zero along the antenna

axis

Er is maximal along the antenna axis dz, zero in the equatorial plane All show axial symmetry

All are proportional to the current moment Idz Have 3 components that decrease with the distance-to-wavelength

ratio as (r/ )-2 & (r/)-3: near-field, or induction field. The energy oscillates from

entirely electric to entirely magnetic and back, twice per cycle. Modeledas a resonant LC circuit or resonator;

(r/ )-1: far-field or radiation field

These 3 component are all equal at (r/) = 1/(2)


54/605


Field components

0.001

0.01

0.1

1

10

100

1000

0.1 1 10

Relative distance, Br

Relativefieldstrength

FF

FF

Q

Q

C

C

FF: Radiation field

C, Q: Induction fields


Field impedance

Fieldimpedance

Z = E/Hdepends

on the

antennatype andondistance

0.01

0.1

1

10

100

0.01 0.1 1 10 100

Distance / (lambda/ 2Pi)

Z/377

Short dipole

Small loop


55/605


Far-Field, Near-Field

Near-field region: Angular distribution of energy depends on

distance from the antenna;

Reactive field components dominate (L, C)

Far-field region: Angular distribution of energy is

independent on distance;

Radiating field component dominates (R)

The resultant EM field can locally be treatedas uniform (TEM)


Poynting vector

The time-rate of EM energy flow per unit area infree space is the Poynting vector

(see http://www.amanogawa.com/archive/docs/EM8.pdf).

It is the cross-product (vector product, right-handscrew direction) of the electric field vector (E)and the magnetic field vector (H): P = E x H.

For the elementary dipole E H and onlyExH carry energy into space with the speed oflight.


56/605


Power Flow

In free space and at large distances, theradiated energy streams from the antenna inradial lines, i.e. the Poynting vector has only

the radial component in spherical coordinates.

A source that radiates uniformly in all directionsis an isotropic source (radiator, antenna).For such a source the radial component of the

Poynting vector is independent of and .


Linear Antennas

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

In the far-field region,the vector components

are parallel to each other Phase difference due to Excitation phase difference

Path distance difference

Method of moments - NEC

...

...

321

321

+++=

+++=

HHHH

EEEErrrr

rrrv

O


57/60


58/60


59/605


Java simulations

Polarization:http://www.amanogawa.com/archive/wavesA.html

Linear dipole antennas:http://www.amanogawa.com/archive/DipoleAnt/DipoleAnt-2.html

http://www.amanogawa.com/archive/Antenna1/Antenna1-2.html

2 antennas:http://www.amanogawa.com/archive/TwoDipole/Antenna2-2.html


Any questions?

Thank you for your attention


60/60


Copyright note

Copyright 2007 Ryszard Struzak. All rights are reserved.

These materials and any part of them may not be published,

copied to or issued from another Web server without the author'swritten permission.

These materials may be used freely for individual study, research,

and education in not-for-profit applications.

If you cite these materials, please credit the author

If you have comments or suggestions, you may send thesedirectly to the author at [email protected].

5anten_theor_bascs

Documents