Transcript Document

SPRAWDZIC #4--6!!!!
Antenna Basics
15 Jan 2003
Property of R. Struzak
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Outline
•
•
•
•
•
•
Reciprocity Theorem
Point Radiator Concept
Irradiance, PFD
Directivity, Gain, Radiation Efficiency
EIRP
Power Transfer
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EM Field = EM Forces
• EM Field is a spatial distribution of forces which
may be exerted on an electric charge
– Force = a vector characterized by its intensity, direction,
& orientation
• Classical physics
– Coulomb (1736-1806), Galvani (1737-1798) Volta
(1745-1827), Ampere (1775-1836), Faraday (17911867), Maxwell (1831-1879), Hertz (1857-1894),
Marconi (1874-1937), Popov (1874-1937)
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EM Field
• EM forces fill-in the whole space without limits.
• They interact with the matter.
– Magnetic forces and electric forces act differently, e.g. the
magnetic field interact with electric charges only when the
charges move.
– For many years Electric and Magnetic forces were
considered as being different phenomena and different
branches of physics. Only in 19 century ……. realized that
they both are different faces of the same EM phenomenon
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• Abdus Salam, (XX-XX), 1979 Nobel Prize
Laureate, indicated further that
electromagnetism and weak interaction
known from quantum physics are various
facets of the same phenomenon.
• Richard Feynmann (1918-1988), 1965
Nobel Prize Laureate ( XXX quantum
electrodynamics)
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EM forces are stronger than gravity forces,
but how strong they are?
• Imagine 2 persons at 1 m distance. By
some magic, we decrease the number of
protons by 1% in each, so that each has
more electrons than protons, and is no
more electrically neutral: they repulse
each other. How strong would be the
repulsive force?
• Could it be enough to move a sheet of
paper? Or this table? Or, perhaps, this
building?
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• Feynman calculated that
the repulsive force would
be strong enough to lift the
whole Earth!
• EM forces generated in far
galaxies can move
electrons on the Earth:
Panzias & Wilson, Nobel
Prize Laureates 1978,
showed that the EM
residual noise was
generated during the Big
Bang
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Maxwell Equations
• Concept of unlimited EM field interacting
with the matter
– Mathematics: 2 coupled vectors E and H
(6 numbers) varying with time and space
• Summary: The magnetic and electric
components of the time-space-variable
electromagnetic field and the time-variable
electric current are mutually coupled.
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EM Field of Linear Antennas
• Summation of all vector
components E (or H)
produced by each antenna
element
O

  
E  E1  E2  E3  ...
 


H  H1  H 2  H 3  ...
• In the far-field region,
the vector components
are parallel to each other
• Method of moments
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EM Field of Current Element
Er
z


 
E  Er  E  E
 


H  H r  H  H
E
OP

I, dz
r
E
y

2
E 
Er  E  E
H 
H r  H  H 
2
2
2
2
2
x
I: monochromatic AC [ampere]; dz: short element [meter]
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EM Field of Current Element 2
E  jA  FF  jQ  C  (sin  )e  j  r
Er  2 A Q  C  (cos  )e  j  r
E  0
jA
H 
 FF  Q  (sin  )e j r
120
H r  H  0

2

A  30 2 Idz
1
FF 
r
1
Q
( r ) 2
1
C
( r )3
Idz: “moment of linear current element”
Johnson & Jasik: Antenna Engineering Handbook; T. Dvorak: Basics of Radiation Measurements, EMC Zurich 1991; J. Dunlop, D. Smith Telecommunications Engineering1995, p. 216
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EM Field of Current Element 3
• The components of the EM field
– are proportional to the current moment Idz
– are azimuth-independent (axial symmetry)
– decrease with distance as (r)-1, (r)-2, or (r)-3;
if r = 1, [r = /(2)], C = FF = Q
• E maximal in the equatorial plane
• Er maximal in the direction of current dz
• H maximal in the equatorial plane
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EM Field: Elementary Current Loop
H  120BFF  jQ  C (sin )e
 jr
H r  2 BQ  C (cos )e  jr
E   BFF  Q (sin )e  jr
 3dm
B
4
H   Er  E  0

2
dm  I  LoopArea

dm: “magnetic dipole moment”
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
Field Components Intensity
1000
C
C, Q: Induction fields
Relative fieldstrength
100
Q
10
FF
1
FF: Radiation field
0.1
FF
Q
0.01
C
0.001
0.1
1
10
Relative distance, Br
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Field Impedance
100
Short dipole
Z / 377
10
1
0.1
Small loop
0.01
0.01
0.1
1
10
Distance / (lambda/ 2Pi)
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Field
impedance
Z = E/H
depends
on the
antenna
type and
on
distance
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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:
–
–
–
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Angular distribution of energy is independent on
distance;
Radiating field component dominates (R)
The resultant EM field can locally be treated as
uniform (TEM)
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Source Characteristics 1
•
The radiated (far) field in all direction
from a single monochromatic source in
free space is completely specified by 4
quantities:
1. Amplitude of the E component of the electric
field as functions of r, , and 
2. Amplitude of the E component of the electric
field as functions of r, , and 
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Source Characteristics 2
3. Phase lag  of E behind E as a function of ,
r, and 
4. Phase lag  of a field component behind its
value at a reference point as a function of r, ,
and 
•
Phase characteristics are often disregarded but
they are important when the fields from 2 or
more sources are to be added.
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Reciprocity Theorem
• The proprieties of a receiving antenna are
identical with the proprieties of the same
antenna when used for transmitting
– Note: This theorem is valid only for linear
passive antennas (i.e. antennas that do not
contain nonlinear elements and/or amplifiers)
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Antenna Functions
• To transform the power of time-dependent electrical
current into the power of the time-and-spacedependent electro-magnetic (EM) wave (transmitting
antenna)
• To transform the power of the time-and-spacedependent EM wave into the power of the timedependent electrical current (receiving antenna)
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Intended & Unintended Antennas
• Intended antennas
– Radiocommunication antennas
– Measuring antennas, EM sensors, probes
– EM applicators (Industrial, Medical)
• Unintended antennas
– Radiating (any conductor/ installation carrying electrical current:
e.g. electrical installation of vehicles)
– Receiving/ Re-radiating (any conducting structure/ installation
irradiated by EM waves)
– Stationary (e.g. antenna masts or power line wires)
– Time-varying (e.g. windmill or helicopter propellers)
– Transient (e.g. aeroplanes, missiles)
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Basic Antenna Characteristics
• In terms of field theory (Electromagnetics)
– Gain
– Radiation pattern (Half-power beam width,
unintended lobes)
– Polarization (Cross-polarization)
• In terms of circuit theory
– Radiation resistance (Impedance)
– VSWR
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Point Source
• For many purposes, it is sufficient to know
the direction (angle) variation of the power
radiated by antenna at large distances.
• For that purpose, any practical antenna,
regardless of its size and complexity, can be
represented as a point-source.
• The actual field near the antenna is then
disregarded.
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Point Source 2
• The EM field at large distances from an
antenna can be treated as originated at a
point source - fictitious volume-less emitter.
• The EM field in a homogenous unlimited
medium at large distances from an antenna
can be approximated by an uniform plane
TEM wave
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Power Flow
• The time rate of EM energy flow per unit area in
free space is the Poynting vector.
• It is the cross-product (vector product, right-hand
screw direction) of the electric field vector (E) and
the magnetic field vector (H) P = E x H.
• For the elementary dipole E  H and only ExH
carry energy into space with the speed of light
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Power Flow 2
• The Poynting vector gives the irradiance and
direction of propagation of the electromagnetic
wave in free space.
• Irradiance = radiant power incident per unit area
upon a surface. It is usually expressed in watts per
square meter, but may also be expressed in joules
per square meter.
• Synonyms: Power Density, Power Flow Density
(PFD).
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Power Flow 3
• In free space, the radiated energy streams from
the point source in radial lines, i.e. the Poynting
vector has only the radial component in
spherical coordinates.
• A source that radiates uniformly in all directions is
an isotropic source (radiator, antenna).
For such a source the radial component of the
Poynting vector is independent of  and .
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Spherical coordinates for a point
source of radiation in free space
Observation
point (r,,)
Polar
axis
Z
Poynting vector
E
Point source
at origin

r
X
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E

Y
Equatorial plane
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Power Flow From Point Source
Z
r sin
Polar
axis
Element of area
ds = r2 sin d d
r d

r
X

Equatorial plane
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Y
r sin d
30
Power Flow - General Case
T he totalcomplexpower flow throughany closed surface:
1
W '   ( E  H *)ds
2
E and H * are complex vectorsof electricand magneticfields,
H * is thecomplexconjugateof H .
ds  r 2 sin  d d is theinfinitisimal elemetof sphericalsurface
T he totalreal power through thesurface:

1
W  ReW '  Re   ( E  H *)ds   Pds   Pr ds

2
1
P  ReE  H * is theP oyntingvector.
2
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Power Flow - Isotropic Source
For an isotropic source in loss-less medium,
Pr is independent of  and  so that
r
W   Pr ds  Pr  ds
The integral is equal to the area of
the sphere (4 r 2 ) and W  Pr 4 r 2 .
W
4 r 2
Pr  PFD (Poynting vector), [Wm -2 ]
Pr 
W  power radiated, [W]
r  distance [m]
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Notes
•
•
•
•
PFD does not depend on frequency/ wavelength
Distance increases x 2 → PFD decreases x 4
Distance increases x 2 → E decreases x 2
Isotropic radiator cannot be physically realized
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Anisotropic sources
• Every antenna has directional
properties (radiates more energy in
some directions than in others).
Isotropic sphere
• Idealized example of directional
antenna: the radiated energy is
concentrated in the yellow region
(cone).
• The power flux density gains: it is
increased by (roughly) the inverse
ratio of the yellow area and the total
surface of the isotropic sphere.
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Antenna Gain
• The ratio of the power required at the input
of a loss-free reference antenna to the power
supplied to the input of the given antenna to
produce, in a given direction, the same field
strength at the same distance.
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Antenna Gain 2
Step 2
Step 1
Actual
antenna
Measuring
equipment
Reference
antenna
Measuring
equipment
P = Power
delivered to
the actual
antenna
S = Power
received
Po = Power
delivered to
the reference
antenna
S0 = Power
received
Antenna Gain = (P/Po) S=S0
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Antenna Gains Gi, Gd, Gr
• Gi “Isotropic Power Gain” - the reference
antenna is isotropic
• Gd - the reference antenna is a half-wave
dipole isolated in space
• Gr - the reference antenna is linear much
shorter than one quarter of the wavelength,
normal to the surface of a perfectly
conducting plane
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Antenna Gain: Comments
• Unless otherwise specified, the gain refers
to the direction of maximum radiation.
• Gain in the field intensity may also be
considered - it is equal to the square root of
the power gain.
• Gain is a dimension-less factor, usually
expressed in decibels
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Radiant Intensity
z

Transmitting
antenna

= Radiated power per unit solid
angle (steradian), (,), in
watts per steradian
Observation
• A measure of the ability of
Point
an antenna to concentrate
radiated power in a
r
particular direction
y
• Does not depend on
distance
x
Assumption: Distance (r) is very large
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Directivity
( ,  ) ( ,  )
D( ,  ) 

 avg
P0 4
Averageradiationintensity
P
 avg  0
4
T otalpower radiated
P0  
2
0
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

0
( ,  ) sin  d d
Property of R. Struzak
• D Has no units
• P0 = power radiated
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Gain, Directivity, Radiation Efficiency
• The radiation intensity,
directivity and gain are
measures of the ability of an
antenna to concentrate power
in a particular direction.
• Directivity relates to the power
radiated by antenna (P0 )
• Gain relates to the power
delivered to antenna (PT)
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G ( ,  )  D( ,  )
PT

P0
• : radiation efficiency
(0.5 - 0.75)
Property of R. Struzak
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Antenna Gain & PFD
 ( ,  )  ( ,  )
S ( ,  ) 

(r )(r )
r2
P0
 G ( ,  )
4r 2
 G ( ,  ) S 0
S0 = PFD produced by a loss-less isotropic radiator
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Directivity Pattern
– The variation of the field intensity of an antenna as an
angular function with respect to the axis.
– Usually represented graphically for the far-field
conditions.
– May be considered for a specified polarization and/or
plane (horizontal, vertical).
– Depends on the polarization and the reference plane for
which it is defined/measured
– Synonym: Radiation pattern.
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Antenna patterns
Pmax()
1

E2
Pr 
 E  Pr Z 0
Z0
E  E2  E2

P()
Power pattern
Z 0  377 ohms
P()/Pmax() for plane wave
Relative (normalized)
power pattern
• Usually represented in 2 reference planes =const. and =const.
• E & PDF relate to the equivalent uniform plane wave
• Note: Peak value = 2 x Effective value for sinusoidal quantities
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Elements of Radiation Pattern
Main lobe
Emax
Sidelobes
Emax /2
Nulls
-180
0
Beamwidth
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180
•
•
•
•
Gain
Beam width
Nulls (positions)
Side-lobe levels
(envelope)
• Front-to-back ratio
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Beam width
• Beamwidth of an
antenna pattern: the angle
between the half-power
points of the main lobe.
• Defined separately for
the horizontal plane and
for the vertical plane.
• Usually expressed in
degrees.
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Antenna Mask (Example 1)
Typical relative
directivity- mask
of receiving
antenna (Yagi
ant., TV dcm
waves)
Relative gain, dB
0
-5
-10
-15
180
120
60
0
-60
-120
-180
-20
[CCIR doc. 11/645, 17-Oct 1989)
Azimith angle, degrees
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Antenna Mask (Example 2)
0
0dB
RR/1998 APS30 Fig.9
Relative gain (dB)
-10
COPOLAR
-3dB
-20
Phi
-30
-40
CROSSPOLAR
-50
0.1
10
1
100
Phi/Phi0
Reference pattern for co-polar and cross-polar components for satellite
transmitting antennas in Regions 1 and 3 (Broadcasting ~12 GHz)
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Typical Gain and Beamwidth
Type of antenna
Gi [dB]
BeamW.
Isotropic
0
3600x3600
Half-wave Dipole
2
3600x1200
Helix (10 turn)
14
350x350
Small dish
16
300x300
Large dish
45
10x10
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Gain and Beamwidth
• Gain and beam-width of highly directive antennas
are inter-related:
G ~ 30000 / (1*2)
• 1 and 2 are the half-power beamwidths
in the two orthogonal principal planes of antenna
radiation pattern in degrees.
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Increasing Gain
Using
multiple
antenna
Using
lenses
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Using
reflector
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Parabolic Antenna
L
A”
A
A’
B’
B”
B
F
C”
C
C’
L’
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Wave front
• For the planar wave front, the
times/distances
FA’A = FB’B = CC’C =…
• Extend AA’ by A’A” …
• Require A’A” = A’F …
• Locus of points equidistant
from F and LL’ is parabola
• Axial symmetry – parabolic
reflector
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How to Make Parabolic Reflectors Cheaply
Water
Steel tube
Explosive
Thin metallic sheet
over parabolic surface
Flat metallic sheet
Air
Parabolic surface
Sand (fixed)
Concrete/iron block
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e.i.r.p.
• Equivalent Isotropically Radiated
Power (in a given direction):
e.i.r. p.  PGi
• The product of the power supplied to the
antenna and the antenna gain (relative to
an isotropic antenna) in a given direction
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Antenna Effective Area
• Measure of the effective absorption area presented
by an antenna to an incident plane wave.
• Depends on the antenna gain and wavelength

2
Ae 
G( ,  ) [m ]
4
2
Aperture efficiency: a = Ae / A
A: physical area of antenna’s aperture, square meters
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Power Transfer in Free Space
PR  PFD  Ae
 GT PT

2
 4r
  GR 


 4 
2
  
 PT GT GR 

 4r 
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2
• : wavelength [m]
• PR: power available at the
receiving antenna
• PT: power delivered to the
transmitting antenna
• GR: gain of the transmitting
antenna in the direction of the
receiving antenna
• GT: gain of the receiving
antenna in the direction of the
transmitting antenna
• Matched polarizations
Property of R. Struzak
56
Linear Polarization
• In a linearly polarized
plane wave the direction
of the E (or H) vector is
constant.
• Two linearly polarized waves produce one
elliptically polarized wave – the resultant E vector
has direction varying in time – its tip draws an
ellipse.
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57
Elliptical Polarization
LHC
Ex = cos (wt)
Ey = cos (wt)
Ex = cos (wt)
Ey = cos (wt+pi/4)
Ex = cos (wt)
Ey = -sin (wt)
RHC
Ex = cos (wt)
Ey = -cos (wt+pi/4)
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Property of R. Struzak
Ex = cos (wt)
Ey = cos (wt+3pi/4)
Ex = cos (wt)
Ey = sin (wt)
58
Ex
Ey
Polarization ellipse
M

N
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• The superposition of
two plane-wave
components results in
an elliptically
polarized wave
• The polarization
ellipse is defined by its
axial ratio N/M
(ellipticity), tilt angle
 and sense of rotation
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Polarization states
LHC
UPPER HEMISPHERE:
ELLIPTIC POLARIZATION
LEFT_HANDED SENSE
(Poincaré sphere)
LATTITUDE:
REPRESENTS
AXIAL RATIO
EQUATOR:
LINEAR POLARIZATION
450 LINEAR
LOWER HEMISPHERE:
ELLIPTIC POLARIZATION
RIGHT_HANDED SENSE
RHC
LONGITUDE:
REPRESENTS
TILT ANGLE
POLES REPRESENT
CIRCULAR POLARIZATIONS
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Comments on Polarization
• At any moment in a chosen reference point in
space, there is actually a single electric vector E
(and associated magnetic vector H).
• This is the result of superposition (addition) of the
instantaneous fields E (and H) produced by all
radiation sources active at the moment.
• The separation of fields by their wavelength,
polarization, or direction is the result of
‘filtration’.
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61
Antenna Polarization
• The polarization of an antenna in a specific
direction is defined to be the polarization of the
wave produced by the antenna at a great distance
at this direction
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62
Polarization Efficiency (1)
• The power received by an antenna
from a particular direction is maximal if the
polarization of the incident wave and the
polarization of the antenna in the wave arrival
direction have:
– the same axial ratio
– the same sense of polarization
– the same spatial orientation
.
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Polarization Efficiency (2)
• When the polarization of the incident wave is
different from the polarization of the receiving
antenna, then a loss due to polarization mismatch
occurs
Polarization efficiency =
= (power actually received) / (power that would be
received if the polarization of the incident wave
were matched to the receiving polarization of the
antenna)
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64
Polarization Efficiency (3)
LCH
A: POLARIZATION OF RECEIVING ANTENNA
W: POLARIZATION OF INCIDENT WAVE
W
2
A
Polarization
efficiency = cos2
450 LINEAR
H
RCH
15 Jan 2003
Property of R. Struzak
65
How to Produce Circularly-Polarized
EM Field
y
x
Ixcos(t+x)
15 Jan 2003
• Radio wave of elliptical
(circular) polarization can
Iycos(t+y)
be obtained by
superposition of 2
linearly-polarized waves
produced by 2 crossed
dipoles and by controlling
the amplitude- ratio and
phase-difference of their
excitations.
Property of R. Struzak
66
Reflection & Image Theory
• Antenna above perfectly
conducting plane surface
• Tangential electrical field
component = 0
– vertical components: the
same direction
– horizontal components:
opposite directions
• The field (above the
ground) is the same if the
ground is replaced by the
antenna image
15 Jan 2003
Property of R. Struzak
+
-
67
Polarization Filters
Wall of thin parallel wires (conductors)
|E1|>0
|E1|>0
|E2| = 0
|E2| ~ |E2|
Vector E  wires
Vector E  wires
• At the surface of ideal conductor the tangential
electrical field component = 0
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Property of R. Struzak
68
e.i.r.p. & PFD: Example 1
• What is the PFD from
a TV broadcast GEO
satellite at Trieste?
1.8  102  103
PFD 
4    (3.8  10  103  103 ) 2
– EIRP: 180 kW
– Distance: ~38'000 km
– Free space
15 Jan 2003
Property of R. Struzak
1.8  105

1.8  1016
 1  1011 Wm-2
 110 dB(Wm 2 )
70
e.i.r.p. & PFD: Example 2
• What is the PFD
from a WLAN
transmitter?
1.8  101
PFD 
4    (3.8) 2
1.8  101

2
1.8  10
3
-2
 1  10 Wm
– EIRP: 180 mW
– Distance: 3.8 m?
– Free space
 30 dB(W m-2 )
In this example, WLAN produces thousand millions times stronger signal than the satellite!
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Property of R. Struzak
71
Power Transfer: Example 1
• What is the power
received from GEO
satellite
(=0.1m, PT =440 W,
GT=1000)
at Trieste
(distance ~38'000 km,
GR=1)?
• Free space
15 Jan 2003
  
PR  PT GT GR 
 
 4r 
2
0.1

2
3 
 4.4  10  10  
6 
 4    38  10 
4.4  105  10 2

4.4  1018
 1  1015 W
 150 dB(W)
Property of R. Struzak
72
2
Power Transfer: Example 2
• What is the power
from a transmitter
(=0.1m, PT=44
mW, GT=1)
received at distance
of 3.8 m (GR=1)?
• Free space
15 Jan 2003
  
PR  PT GT GR 
 
 4r 
2
0.1 

3
 4.4  10  1  1  

 4    3.8 
2
4.4  103

4.4  102
 105 W
 50 dB(W)
Property of R. Struzak
73
Mismatch Effects
SWR
15 Jan 2003
Gain Reduction Gain Reduction
1.0
0
0
1.5
4%
0.2 dB
2.0
11%
0.5 dB
3.0
25%
1.3 dB
5.0
44%
2.6 dB
10
67%
4.8 dB
Property of R. Struzak
74
2 Identical Antennas
r
• Excitation:
I1 = I; I2 =Iej
rr
r

• Ant#1 field-strength:
E’= C*D(, )
2
d
1
r = d*cos 
• Ant#2 field-strength:
E” = [C*D(,
)]*ej(r+)
15 Jan 2003
Property of R. Struzak
75
2 Identical Antennas - AAF
• Resultant field-strength
E = E’ + E”
• E = E’ *[1+ej(r+)]
= C*D(, )*[1+ej(r+)]
= C*D(, )*F(, )  Pattern multiplication
• AAF(, ) = | F(, ) |2
= Antenna array factor
= Gain of array
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76
2 Antenna Array Factor (1)
• F() = 1+ej(r+) ;
(r+) = x
• F() = 1+ejx = 2[(1/2)(e-jx/2 +ejx/2)]ejx/2
= 2[cos(x/2)]ejx/2
• |F()| = 2cos(x/2)
= 2cos[(d/2)cos + /2)
= 2cos[(d/)cos + /2]
• |F()|2  Antenna Array Factor
= gain of 2 isotropic antennas
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77
2 Antenna Array Factor (2)
• |F()|2 = {2cos[(d/)cos + /2]}2
• Gain: Max{|AAF()|2} = 4 (6 dBi)
when (d/)cos + /2 = 0, , …, k
• Nulls: when (d/)cos + /2 = /2, …, (k + 1)/2
• Relative gain = |AAF()|2 / Max{|AAF()|2}
= {cos[(d/)cos + /2]}2
Array2ant simulation
15 Jan 2003
Property of R. Struzak
78
Isotropic Antenna Over Conducting Plane
2AntOverPlane simulation
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Linear Array of n Antennas
• equally spaced
• F = 1+ejx+ej2x+ej3x+…+ej(N-1)x
antennas in line
= (1-ejNx) / (1-ejx)
• currents of equal
magnitude
• |F| = |(1-ejNx) / (1-ejx)|
• constant phase
= [sin(Nx/2) / sin(x/2)]
difference between
= F()  array factor
adjacent antennas
• numbered from 0
to (n-1)
• x/2 = (d/)cos + /2
Array_Nan simulation
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80
Phased Arrays
• Array of N antennas in a linear or spatial
configuration
• The amplitude and phase excitation of each
individual antenna controlled electronically
(“software-defined”)
– Diode phase shifters
– Ferrite phase shifters
• Inertia-less beam-forming and scanning (sec)
with fixed physical structure
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81
Antenna Arrays: Benefits
• Possibilities to control
–
–
–
–
–
Direction of maximum radiation
Directions (positions) of nulls
Beam-width
Directivity
Levels of sidelobes
using standard antennas (or antenna collections)
independently of their radiation patterns
• Antenna elements can be distributed along straight
lines, arcs, squares, circles, etc.
15 Jan 2003
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82
Beam Steering
Beam direction

d
3
2

• BeamEqui-phase
steering
wave front
using
phase
 = [(2/)d sin]
shifters at
Radiating
each
elements
radiating
Phase
0
shifters
element
Power
distribution
15 Jan 2003
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83
4-Bit Phase-Shifter (Example)
Bit #3
Bit #4
Input
00
or
22.50
00
or
450
Bit #1
Bit #2
00
or
900
00
or
1800
Output
Steering/ Beam-forming Circuitry
15 Jan 2003
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84
Switched-Line Phase Bit
Delay line
Input
Output
Diode switch
2 delay lines and 4 diodes per bit
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85
Switching Diode Circuit
PIN
diode
PIN
diode
Tuning
element
Tuning
element
b
a
a: RF short-circuited in forward bias
b: RF short-circuited in reverse bias
15 Jan 2003
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86
Adaptive (“Intelligent”)Antennas
•
•
•
•
•
Array of N antennas in a linear
or spatial configuration
Used for receiving signals from
desired sources and suppress
incident signals from undesired
sources
The amplitude and phase
excitation of each individual
antenna controlled
electronically (“softwaredefined”)
The weight-determining
algorithm uses a-priori and/ or
measured information
The weight and summing
circuits can operate at the RF or
at an intermediate frequency
15 Jan 2003
1
w1

wN
N
Weight-determining
algorithm
Property of R. Struzak
87
Direction Separation
RECEIVER
unwanted transmitter
wanted transmitter
U
W
15 Jan 2003
Property
of R. Struzak
Adaptive
antennas
88
Directive Antenna Effectiveness
• An ideal directive antenna
receives power coming
only from within apical
angle 
• It can eliminate (or
attenuate) radiation
coming from a limited
number of discrete
interferers (but cannot
eliminate isotropic noise)
15 Jan 2003
Property of R. Struzak
89
Directive Antenna Effectiveness
Rec
J
T
Effective
(T within antenna beam
J outside)
15 Jan 2003
Rec
Rec
J
J
T
Limiting case
(T and J at
edges)
Property of R. Struzak
T
Not effective
(T and J within
antenna beam)
90
Directive Antenna Effectiveness
Receiver


2    
2    
R
 
R  R

h

T
2      2
2  2   
  
A
R
2sin 


J
A
h  R cos   cot 
2
A
15 Jan 2003
Property of R. Struzak
91
Directive Antenna Effectiveness
Rc
Plane Surface 

T
T
 2 R 2 (    sin 2 ) 
J
A2     sin 2

2
sin 2 
Volume (rotation around T - J ) 

 h 
 2 hR arcsin1  arcsin    
 R 

3
4
2
2
2
2
2
2 h R  h 
R h
3
2

15 Jan 2003
Property of R. Struzak

92
Various Antenna Types (Pictures)
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93
Antenna Summary
• Antenna: substantial element of radio link
• We have just reviewed
–
–
–
–
15 Jan 2003
Basic concepts
Radio wave radiation physics
Elementary radiators
Selected issues relevant to antennas
Property of R. Struzak
94
Antenna References
• Scoughton TE: Antenna Basics Tutorial Microwave Journal
Jan. 1998, p. 186-191
• Kraus JD: Antennas, McGraw-Hill Book Co. 1998
• Stutzman WL, Thiele GA: Antenna Theory and Design
JWiley &Sons, 1981
• Johnson RC: Antenna Engineering Handbook McGraw-Hill
Book Co. 1993
• Pozar D. “Antenna Design Using Personal Computers”
• Li et al., “Microcomputer Tools for Communication
Engineering”
• Software
– http://www.feko.co.za/apl_ant_pla.htm
– www.gsl.net/wb6tpu /swindex.html (NEC Archives)
15 Jan 2003
Property of R. Struzak
95