More Related Content Similar to Antenna & Array Fundamentals Technical Training Courses Sampler (20) More from Jim Jenkins (20) Antenna & Array Fundamentals Technical Training Courses Sampler1. Course Sampler From ATI Professional Development Short Course
Antenna and Antenna Array Fundamentals
Instructor:
Dr. Steven Weiss
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3. What you will learn from this course
• Basic antenna concepts and definitions
• The appropriate antenna for your
application
• Factors that affect antenna array designs
and antenna systems
• Measurement techniques commonly used
in anechoic chambers
Copyright 2012 © by Steven Weiss – all rights reserved
5. Example of a “Real World” Radar Antenna Array
The MU (Middle and Upper atmosphere) radar constructed by the Radio Atmospheric Science Center of Kyoto University at Shigaraki,
Shiga prefecture, Japan
• Investigates atmospheric and plasma dynamics in the wide region from the troposphere to the ionosphere.
• The radar is a powerful monostatic pulse Doppler radar operating at 46.5MHz
• It uses active phased array antenna, which consists of 475 crossed Yagi antennas and identical number of solid-state transmit/receive modules.
• The antenna beam direction can be switched to any direction within the steering range of 30deg from zenith from pulse to pulse.
• The antenna aperture is 8,330m^2 (103m in diameter), and the peak and average output power is 1MW and 50kW, respectively.
• The antenna beam has a conical shape with the round-trip (two-way) half-power beamwidth of 2.6deg. 4
Copyright 2012 © by Steven Weiss – all rights reserved
6. Examples of Antennas
The VLA is an array of telescopes that can be linked CSIRO Parkes radio telescope is the largest and oldest
together to synthesize the resolving power of a telescope of the eight antennas comprising the 'Australian
upto 36 km (22 miles) across, or grouped together to Telescope National Facility'. The Compact Array of six
synthesize one only a km (0.6 mile) across: the varying 22-metre dishes near Narrabri and another near
resolutions are the equivalent of an astronomical zoom Coonabarabran link up with the 64 meter Parkes to
lens. This array is located near Socorro, NM synthesize a telescope some 300 kilometers across.
5
Copyright 2012 © by Steven Weiss – all rights reserved
8. Missile Defense
Eglin FPS-85 radar located near Ft. Walton Working inside a 10-story Pave Phased Array Warning System, or
Pave PAWS, the men and women of the 7th Space Warning
Beach, FL. This phased array radar is a dedicated Squadron continuously scan the horizon for missiles, satellites and
sensor to the U.S. satellite catalog. other man-made objects in space.
7
Copyright 2012 © by Steven Weiss – all rights reserved
9. European Remote Sensing satellite (ERS) Inmarsat
Provides information about the Used for Global Communications
Earth’s land, oceans and polar caps
8
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12. Types of Antennas
• Electrically small antennas
• Resonant antennas
• Broadband antennas
• Aperture antennas
11
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13. Electrically Small Antennas
The extent of the antenna structure is much less than the wavelength
• Very low directivity
• Low input resistance
• High input reactance
• Low radiation efficiency
Short Dipole
Small Loop
12
Copyright 2012 © by Steven Weiss – all rights reserved
14. Resonant Antennas
The antenna operates well at a single or selected narrow frequency band
• Low to moderate gain
• Real input impedance
• Narrow bandwidth
~ ~
2 2
Half-wave Dipole
~
2
Yagi
Microstrip Patch
13
Copyright 2012 © by Steven Weiss – all rights reserved
15. Broadband Antennas
The pattern, gain, and impedance remain acceptable and are nearly constant
over a wide frequency range. They are characterized by an active region with
a circumference of one wavelength or an extent of a half-wavelength which
relocates on the antenna as the frequency changes
• Low to moderate gain
• Constant gain
• Real input impedance
• Wide Bandwidth
Spiral
Log-periodic dipole array 14
Copyright 2012 © by Steven Weiss – all rights reserved
16. Aperture Antennas
Have a physical aperture through which the waves flow.
• High Gain
• Gain increases with frequency
• Moderate bandwidth
Aperture Aperture
15
Copyright 2012 © by Steven Weiss – all rights reserved
17. Basic Concepts
• Directivity
• Gain
• Antenna Patterns
• Beamwidth
• Polarization
• Bandwidth
• Radiation Resistance/Input impedance
• Reciprocity
• Effective Aperture 16
Copyright 2012 © by Steven Weiss – all rights reserved
18. What is the directivity of antenna?
Ratio of radiation intensity in a given direction
to the radiation intensity that would be
obtained if the total power radiated by the
antenna were to be radiated isotropically
What is the gain of antenna?
Ratio of radiation intensity in a given direction to
the radiation intensity that would be obtained if
the total power accepted by the antenna were to
be radiated isotropically
17
Copyright 2012 © by Steven Weiss – all rights reserved
19. Simple Illustration (light bulb)
Radiating with equal intensity in all
directions (isotropic radiation) Power meter reading radiated
power (isotropic)
P (isotropic)
Radiation is focused in a particular
direction due to the reflector
Power meter reading of radiated
power (in a given direction)
P (direction)
18
Note that polarization must –be considered with RF antennas
Copyright 2012 © by Steven Weiss all rights reserved
20. Directivity and Gain
• The directivity can be thought of as the ratio of the maximum radiation
intensity emanating from an antenna to the total power leaving the antenna
radiated isotropically per solid angle of a sphere.
• The radiation intensity of an isotropic source is: (Prad ) / (solid angle of a
sphere).
U isotropic Pradiated / 4
• The gain of an antenna can be thought of as the ratio of the maximum
radiation intensity emanating from an antenna to the total power introduced
into the antenna: (Pin ) / (solid angle of a sphere).
• Losses prevent the power input into the antenna from equaling the radiated
power.
Prad Pin
• The gain of an antenna is always less than the
directivity of a antenna. 19
Copyright 2012 © by Steven Weiss – all rights reserved
21. Formulas for Directivity and Gain
U , U , max
D , Do
Prad Prad
4 4
U , U ,
G , D ,
Pin Prad
4 4
U , max U , max
Go Do
Pin Prad
4 4
Gain is usually expressed in log form :
G dBi 10 Log ( Do ) 10 Log ( Do ) 10 Log ( ) 20
Copyright 2012 © by Steven Weiss – all rights reserved
22. A Directed Beam is Described by its
Antenna Pattern
Main lobe
Side lobes
Back lobes
21
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23. More Details about Radiation
Patterns
Beamwidth (between 3 dB points)
22
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24. Patterns
Omni-directional pattern Hemispherical pattern
Equal power everywhere Isotropic pattern
Equal power in one plane.
in upper half-plane. Equal power everywhere.
23
Copyright 2012 © by Steven Weiss – all rights reserved
25. Polarization
• Electric fields must be aligned for maximum
power transfer between two antennas.
• The alignment is described by a polarization loss
factor (PLF).
• Analytically, the polarization loss factor is the
electric field of the incoming wave dotted with
the electric field that would be transmitted by
the receiving antenna.
24
Copyright 2012 © by Steven Weiss – all rights reserved
26. An Introduction to Polarization
• When speaking of “polarization,” we are describing
the behavior of electric field of the antenna.
• The field may remain oriented in one direction as the
electric field propagates (linear polarization)
• The field may spin as the electric field propagates
(circular or elliptical polarization)
• Polarization will be considered in detail later in this
course, but you already have enough material to
understand how our math can describe such electric
fields!
25
Copyright 2012 © by Steven Weiss – all rights reserved
27. An Introduction to Polarization
Here is an interesting antenna that has two input ports. We will
designate these as port 1 and port 2
Port 2
Port 1
26
Copyright 2012 © by Steven Weiss – all rights reserved
28. An Introduction to Polarization
Port 2
Port 1
Y
Add
some
geometry
!
X
27
Copyright 2012 © by Steven Weiss – all rights reserved
29. An Introduction to Polarization
Exciting port 1 causes an electric field to exist between the two horizontal fins
and the field at the “aperture” of the antenna is oriented in the x-direction
E a x Eo
ˆ
Port 1
Y
X
28
Copyright 2012 © by Steven Weiss – all rights reserved
30. An Introduction to Polarization
Exciting port 2 causes an electric field to exist between the two vertical fins
and the field at the “aperture” of the antenna is oriented in the y-direction
E a y Eo
ˆ
Port 2
Y
X
29
Copyright 2012 © by Steven Weiss – all rights reserved
31. An Introduction to Polarization
We already know that we can represent time-varying fields as phasors.
If we excited both ports at once (with equal strength) , we expect the
phasor representation of the electric field at the aperture to be of the
form:
E a x Eo a y Eo
ˆ ˆ
The time-dependent behavoir at the aperture becomes:
j t
(t ) Re[ (a x E o a y E o ) e
ˆ ˆ ] (a x E o a y E o ) Cos ( t )
ˆ ˆ
It is illustrative to plot this electric field using certain "snapshots" of time.
Holding "" as a constant, there is an instant when the product t equals
zero. Similarly, there are different instances when t equals /2 and
and 3 /2 and so forth. Letting E o 1 V / m, we can make a table and
parametrically plot the time-dependent electric field at the aperture. 30
Copyright 2012 © by Steven Weiss – all rights reserved
32. An Introduction to Polarization
t (a x a y ) Cos ( t )
ˆ ˆ
t
0 (a x a y )
ˆ ˆ
/2 0 X
(a x a y )
ˆ ˆ t /2
3 / 2 0 t 0
Y
The y-axis is pointed downward so that the z-axis would be into the page.
We observe the behavior of the electric field at z 0 (at the aperture.)
The electric field is linearly polarized oriented at a 45 Degree angle with the
y-axis (the tilt angle " .") It is also at a 45 Degree angle with the x-axis,
but we define the tilt angle with respect to the y-axis. 31
Copyright 2012 © by Steven Weiss – all rights reserved
33. An Introduction to Polarization
Now we make one "small" change to our phasor representation of
ˆ
the electric field at the aperture placing a "j" in front of the a y term:
So,
E a x Eo j a y Eo
ˆ ˆ
This term has a significant impact on the time-dependent behavoir of
the elctric field:
j t
(t ) Re[ (a x E o j a y E o ) e
ˆ ˆ ]
Re[ (a x E o j a y E o ) (Cos ( t ) j Sin ( t )) ]
ˆ ˆ
a x E o Cos ( t ) a y E o Sin ( t )
ˆ ˆ
Again, we hold "" as a constant and parametrically plot the time-
dependent electric field at the aperture. Again, let E o 1 V / m.
32
Copyright 2012 © by Steven Weiss – all rights reserved
34. An Introduction to Polarization
t a x Cos ( t ) a y Sin ( t )
ˆ ˆ
0 ˆ
ax
/2 ay
ˆ t /2
ax
ˆ
3 / 2 ˆ
ay
X
t t 0
t 3 / 2
Y
The electric field is spinning in a counter-clockwise direction!
33
Copyright 2012 © by Steven Weiss – all rights reserved
35. An Introduction to Polarization
Is it right-hand or left-hand polarization?
1) Place your thumb towards the direction of propagation. This would be
into the page.
2) If your fingers align with the "spin" you have answered the question!
Try it with each hand and you will find that this example is left-hand
circularly polarized (LHCP.) t /2
X
t t 0
t 3 / 2 34
Copyright 2012 © by Steven Weiss – all rights reserved
Y
36. An Introduction to Polarization
So, is left-hand polarization counterclockwise and right-hand clockwise?
Answer: Not enough information!
You must state whether the field is "leaving" or "arriving."
A thumb pointed away from you indicates a leaving wave.
A thumb pointed toward you indicates an arriving wave.
le ft-h a n d is le ft-h a n d is r ig h t-h a n d is r ig h t-h a n d is
c o u n te rc lo c k w is e c lo c k w is e c lo c k w is e c o u n te r c lo c k w is e
le a v in g a rr iv in g le a v in g a r r iv in g 35
Copyright 2012 © by Steven Weiss – all rights reserved
37. An Introduction to Polarization
Port 2
Port 1
Y
X
This antenna is capable of exciting orthogonal electric fields (i.e., in the x- and y-directions.)
If the fields are excited in phase, the field leaving the antenna will be linearly polarized
leaving the antenna at a 45 Degree angle – if the signal strength is the same at both feeds.
For example: Port 1 = V o Cos ( t ) and Port 2 = V o Cos ( t )
36
Copyright 2012 © by Steven Weiss – all rights reserved
38. An Introduction to Polarization
Port 2
Port 1
Y
X
Again, the antenna is capable of exciting orthogonal electric fields (i.e., in the x- and y-
directions.) If the fields are excited in phase quadrature, the field leaving the antenna will
be circularly polarized – if the signal strength is the same at both feeds.
For example: Port 1 = V o Cos ( t ) and Port 2 = V o Sin ( t )
37
Copyright 2012 © by Steven Weiss – all rights reserved
39. An Introduction to Polarization
We could achieve circular polarization with and RF source, a power splitter, and a 90 Degree
phase shifter.
Power Splitter
90
RF Source
38
Copyright 2012 © by Steven Weiss – all rights reserved
40. Polarization (elliptical)
y , x Assume any value
Ex , E y Not necessarily equal
OA
AR Axial Ratio
OB
1 AR
+ for RH polarization
- for LH polarization
Tilt angle
1 1 2 E x E y
tan cos
Ex 2 E y
2
2 2
39
x y
Copyright 2012 © by Steven Weiss – all rights reserved
42. Polarization Loss Factor
2
EInc ETrans
PLF 2 2
EInc ETrans
EInc ETrans
w
ˆ a
ˆ
EInc Etrans
2
PLF w a
ˆ ˆ
The electric fields are in phasor form and
may be complex quantities
Copyright 2012 © by Steven Weiss – all rights reserved
41
43. Polarization
Polarization is a critical issue when considering antennas
Proper alignment – Maximum power transferred from antenna A to antenna B.
A B
Antenna “A” transmits a Antenna “B” is oriented
vertically polarized signal to receive a vertically
polarized signal
Improper alignment – Minimum power transferred from antenna A to antenna B.
A B
Antenna “A” transmits a Antenna “B” is oriented
vertically polarized signal to receive a horizontally
polarized signal
Circular to linear – 1 / 2 the power transferred from antenna A to antenna B.
A B
Antenna “A” transmits a Antenna “B” is oriented to receive
circularly polarized signal linear polarization in any direction 42
Copyright 2012 © by Steven Weiss – all rights reserved
44. Bandwidth
• There are 3 equivalent ways do describe the
bandwidth of an antenna
– Return loss (-10 dB convention)
– VSWR (2:1 convention)
– Polar Plot (Smith chart) 0.316228
43
Copyright 2012 © by Steven Weiss – all rights reserved
45. Definition of the Reflection Coefficient
Characteristic impedance of the transmission line
Transmitted Voltage
V
Zo
V
Reflected Voltage
Reflection Coefficient – a complex ratio of the
V reflected voltage divided by the transmitted voltage
V measured at a defined reference place (e.g., the input
port of the antenna.
44
Copyright 2012 © by Steven Weiss – all rights reserved
46. Reflected Power
r j i r j i
2 * 2 2
r i
2
1
2
2
Percentage of power reflected from the antenna
1
2
Percentage of power entering the antenna
Note that the power entering the antenna is not equal to the power radiated
by the antenna. Some power is consumed in conductor and other losses
45
Copyright 2012 © by Steven Weiss – all rights reserved
47. Bandwidth – A Logarithmic Plot
A return loss of -10 dB is conventionally defines as the bandwidth of the antenna
Bandwidth f H f L
0 fH
fL -5
- 10
dB
- 15
- 20
- 25
2 4 6 8 10
Frequency
fo 46
Copyright 2012 © by Steven Weiss – all rights reserved
48. Bandwidth – VSWR Plot
1
2
1.75
1.5
1.25 The impedance mismatch between the
1 Antenna’s input impedance and the
0.75 characteristic impedance of the
0.5 transmission line causes a standing
wave to exist along the length of the
0.25
transmission line.
0.2 0.4 0.6 0.8 1
Distance back from the reference plane
Frequency
1 6
5
Bandwidth f H f L 4
V SWR
3
VSWR
1 2
fH
1
fL 1
fo 2 4 6 8
47
10
Copyright 2012 © by Steven Weiss – all rights reserved
Frequency
49. Bandwidth – Polar Plot
I
Bandwidth f H f L 1
Discrete Data points
measured on a
fL
Network Analyzer
R
fH fo
0.316228 48
Copyright 2012 © by Steven Weiss – all rights reserved
50. Bandwidth – Polar Plot/Smith Chart
From transmission line theory I
ZL Zo
R j I
ZL Zo
When the real and
fL
imaginary parts of the load
impedance are
determined as a function
of the real and imaginary R
parts of the reflection
coefficient, the resulting fH
fH
circles and arcs define the
Smith Chart.
0.316228 49
Copyright 2012 © by Steven Weiss – all rights reserved
51. Realized (or actual) Gain
Grealized ( 1 ) Go ( 1 ) Do
2 2
50
Copyright 2012 © by Steven Weiss – all rights reserved
52. Bandwidth – Equivalent Quantities
Return Loss VSWR 1
2
0.316228 -10 dB 1.9245 0.9
0.100000 -20 dB 1.2222 0.99
0.031622 -30 dB 1.0653 0.999
51
Copyright 2012 © by Steven Weiss – all rights reserved
53. Antenna Impedance
(Transmit)
The input impedance is the
impedance presented by an
antenna at its terminals
generator a radiated waves
Zg
b
Z A RA jX A
radiation resistance
RA RR RL
52
Copyright 2012 © by Steven Weiss – all rights reserved
54. Input Impedance of Antennas (Transmit)
Vg Vg From circuit theory
Ig
ZA Zg ( RR RL Rg ) j ( X A X g )
2
1 2 Vg Rr
Pr I g RR Power delivered to the
2 2 ( RR RL Rg ) 2 ( X A X g ) 2
antenna for radiation
Power dissipated as
2
1 2 Vg RL
PL I g RL heat on the antenna
2 2 ( RR RL Rg ) 2 ( X A X g ) 2
2 Power dissipated as heat
1 2 Vg Rg on the internal resistance
Pg I g Rg
2 2 ( RR RL Rg ) 2 ( X A X g ) 2 of the generator
ZA Zg
*
Conjugate matched conditions deliver
the the maximum power to the antenna. RR RL Rg
X A X g
53
Copyright 2012 © by Steven Weiss – all rights reserved
55. Input Impedance of Antennas (transmit)
2
Vg Rr Radiated power assuming conjugate matching
Pr
8 ( RR RL ) 2
2
Vg RL Dissipated power in the antenna assuming conjugate matching
PL
8 ( RR RL ) 2
2 2
Vg Rg Vg Dissipated power in the generator’s internal impedance
Pg
8 ( RR RL ) 2
8 Rg
The total power is: Pg PR PL
2
Power supplied by the 1 Vg 1
generator : Pg Vg I g
*
2 4 RR RL
Therefore, under conjugate match conditions, half the power that is
supplied by the generator is dissipated as heat in its internal resistance
and the other half is delivered to the antenna.
54
Copyright 2012 © by Steven Weiss – all rights reserved
56. Antenna Impedance
(receive)
Again, the input impedance is
the impedance presented by
an antenna at its terminals
55
Copyright 2012 © by Steven Weiss – all rights reserved
57. Input Impedance of Antennas (receive)
Assuming conjugate matched conditions delivering the maximum power to the antenna.
2
VT Power delivered to the antenna’s terminating impedance
PT
8 RT
VT 2
RR Power across the radiation resistance of the antenna
Pr
8 ( R R R L )2
VT
2
RL
PL 2 Power dissipated as heat due to the losses in the antenna
8 (R R RL )
56
Copyright 2012 © by Steven Weiss – all rights reserved
58. Reciprocity for Antennas
V2 ( , ) I2
1 2
I1 V1 ( , )
Transmitting pattern of antenna “1” Receiving pattern of antenna “2”
V2 ( , ) V2 ( , )
Z12 ( , ) Z 21 ( , )
I1 I1
Z12 ( , ) Z 21 ( , )
Important Point!!! The transmit and receive patterns of an antenna are
the same for a reciprocal antenna. 57
Copyright 2012 © by Steven Weiss – all rights reserved
59. Aperture Size
• Antenna engineers frequently discuss antennas in
terms of Aperture Size.
• A common term is the “effective aperture” size.
• Another term is the “physical aperture” size.
• Aperture size is related to the beamwidth and
accordingly the directivity and gain.
ZL
58
Copyright 2012 © by Steven Weiss – all rights reserved
60. Effective Aperture Size
• The effective aperture size is a relationship between the
incident electromagnetic field and the power delivered to the
terminating impedance on the antenna’s input port.
PT
Aeffective (m 2 )
Wincident
PT The power developed across the terminating impedance (w)
Wincident The strength of the incident electromagnetic field
at the aperture of the antenna (w/m 2 )
PT
Wincident ZL
59
Copyright 2012 © by Steven Weiss – all rights reserved
61. Effective Aperture Size
• The effective aperture size is related to the directivity of the antenna
• Anything that diminishes the power across the terminating impedance
decreases the effective aperture size
• If no power develops across the terminating impedance, the effective
aperture size is zero - even if there is an incident electromagnetic field.
2
Ae m DO (m 2 )
4
PT 2 2
Ae cd
(1 ) DO w a
2
ˆ ˆ (m 2 )
W inc 4
PT
Wincident ZL
60
Copyright 2012 © by Steven Weiss – all rights reserved
62. Physical Aperture Size and
Aperture Efficiency
Area Length x Width Area r 2
Ae m Maximium Effective Aperture
ap
Ap Physical Area 61
Copyright 2012 © by Steven Weiss – all rights reserved
64. Friis Transmission Formula
Time average power density transmitted by satellite Satellite
Antenna
Pr W Aer effective aperture of Pt , Gt
receiving antenna R
total transmitted power Gr
dish
antenna
Pt
W Gt gain of transmitting antenna
4 R 2
4 2
Gr 2 Aer so Aer Gr
4
2
Friis transmission formula Pr Pt Gt Gr
(4 R) 2
63
Copyright 2012 © by Steven Weiss – all rights reserved
65. Communication Link
Gt ( t , t ) Gr ( r , r )
R
ZL
Pr 2
(1 t ) (1 r ) ( ) Gt ( t , t ) Gr ( r , r ) w a
2 2 2
ˆ ˆ
Pt 4 R
64
Copyright 2012 © by Steven Weiss – all rights reserved
66. Communication Links in dBm
Power Milliwatts
Pr (dBm) 10 Log10
1 Milliwatt
2
Friis transmission formula Pr Pt Gt Gr
(4 R) 2
G (dB) 10 log G
Divide each side by 1 mw and take the log
Pr (dBm) Pt (dBm) Gt (dB) Gr (dB )
20 log R (km) 20 log f ( MHz ) 32.44
c C = Speed of light
Note:
f F = frequency
65
Copyright 2012 © by Steven Weiss – all rights reserved
67. The Friis Transmission Formula
Our work with the Friis transmission
formula presumed a rather pristine
environment where one did not have
to worry about the attenuation through
the atmosphere. Of course, these
effects cannot be ignored. Shown to
the left is a plot of attenuation effects
due to oxygen and water vapor.
Accordingly, any link budget would need
to be adjusted to take these (and other)
propagation effects into account. At this
point we begin to leave the study of
antenna theory and enter the realm of
propagation theory.
R. E. Collin, Antennas and Radiowave Propagation, New York, McGraw Hill, 1985, pp 409.
66
Copyright 2012 © by Steven Weiss – all rights reserved
68. Much more!!!
67
Copyright 2012 © by Steven Weiss – all rights reserved
69. To learn more please attend ATI course
Hyperspectral and Multispectral Imaging
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