Wireless LANs
Sep – Dec 2014
Antenna
รศ. ดร. อนันต์ ผลเพิม่
Assoc. Prof. Anan Phonphoem, Ph.D.
anan.p@ku.ac.th
Intelligent Wireless Network Group (IWING Lab)
http://iwing.cpe.ku.ac.th
Computer Engineering Department
Kasetsart University, Bangkok, Thailand
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Outline
• Decibel
• Antenna Radiation Pattern
• 2.4 GHz Antennas
• Cantenna
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Decibel
• A measurement unit
• In logarithmic
• Relative value (Ratio)
• For power / intensity / sound level / voltage
• dB
• LdB = ratio in decible = Gain
P
LdB = 10 log10( P1 )
2
3
Example
P2
• 2 Loudspeakers P1
• Speaker 1: plays sound with Power P1
• Speaker 2: plays sound with Power P2
• Same environment (frequency, distance)
P
LdB = 10 log10( P2 )
1
Condition
Calculation
Decible
P2 = P1
10 log10(1)
0 dB
P2 = 2 P1
10 log10(2)
+3 dB
P2 = 0.5 P1
10 log10(0.5)
– 3 dB
P2 = 10 P1
10 log10(10)
+10 dB
http://www.phys.unsw.edu.au/jw/dB.html
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For Electrical Power
• Power Gain (GdB)
• Calculate 1000 W relative to 1 W
 GdB = 10
1000 W
log10(
1W
) = 30 dB
30 dBW
• Calculate 0.1W relative to 1 mW (milliwatt)
 GdB = 10
100 mW
log10(
)
1 mW
= 20 dB
20 dBm
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Isotropic Antenna
•
•
•
•
•
Radiate same power in all directions
In practice, no 100% isotropic antennas
A perfect isotropic antenna, called "isotropic radiator"
Used for measuring the signal strength of real antennas
Contrast with “Anisotropic Antenna”
• A directional antenna
• Power level is not the same in all directions
http://partnerwiki.cisco.com/ViewWiki/
images/2/2b/Omni-vs-direct2-82068.gif
6
Antenna Gain
•
•
Ratio of the power density of an antenna’s radiation
pattern in the direction of strongest radiation to that of
a reference antenna
dBi (DeciBel Isotropic)
• The measurement of (forward) gain of a directional
antenna
• compared with the Hypothetical Isotropic
Antenna
http://upload.wikimedia.org/wikibooks/en/5/58/Non_isotropic_radiator.gif
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Example
• A directivity of 0 dBi (dB relative to isotropic)
• The radiator equally transmits (or receives)
electromagnetic radiation to/from any arbitrary
direction
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Antenna Gain
• usually represent graphically in polar
coordinates
• As antenna’s energy conservation
• positive gain in some directions
• must have negative gain in other directions
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Antenna Pattern
• Also called “Radiation Pattern”
• Graphical representation
• Describes how the antenna radiates energy
out into space (or how it receives energy)
• Antenna radiates is actually 3D
• Two planar (principle) patterns
• Obtained by making two slices through the 3D
pattern
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Antenna Radiation Pattern
Antenna Axis
Modified from: www.ece.nus.edu.sg/.../Teaching/EE4101/index.htm
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Radiation Patterns
Polar and Cartesian Coordinates
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Polar Coordinate system
• A two-dimensional coordinate system
• Each point on a plane is determined by
• A distance from a fixed point (pole)
• An angle from a fixed direction (polar angle or
azimuth)
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Antenna Measurement
Coordinate System
The azimuth is the angle formed
between a reference direction
(North) and a line from the
observer to a point of interest
projected on the same plane as
the reference direction
http://en.wikipedia.org/wiki/Azimuth
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Azimuth (polar angle)
Polar Grid
Polar
http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps
469/prod_white_paper0900aecd806a1a3e.html
http://en.wikipedia.org/wiki/Polar_coordinate_system
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2.4 GHz Antennas
• Omnidirectional antenna
• Dipole Antenna
• 5.8 dBi Omnidirectional Antenna
• Multiple Element Dipole Antennas
• Yagi Antennas
• Flat Panel antennas
• Parabolic Dish antennas
• Slotted Antennas
• Microstrip Antennas
Partial document from:
Aerocomm, Lenexa, KS
“Antenna Tutorial”
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Omni-directional Antenna
http://som1.csudh.edu/fac/lpress/471/hout/wireless/antennae.htm
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Dipole
•
•
ve3elb.ham-radio.ch/projects.html
Best used for Tx/Rx from broadside
Not a directive antenna
sin2
Elevation Pattern
(Horizontal Pattern)
Works well 360
around antenna
Generic Dipole
Azimuth Pattern
(Vertical Pattern)
http://www.engnetbase.com/
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Dipole Antenna
with 3D Radiation Pattern
http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html
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5.8 dBi Omnidirectional Antenna
http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html
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Directional Antenna
http://en.wikipedia.org/
back lobe
•
Main lobe (beam)
•
•
•
contains max power
greatest field strength
bigger than the others lobes
•
Beamwidth
•
expressed in degrees
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Yagi
• Directional Antenna
• Not as directional as parabolic
dish antenna
• An array of independent
antenna (director) elements
• Only one element driven to
•
transmit electromagnetic waves
The other determines the gain
and directivity
Elevation Pattern
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Yagi
http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html
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2.4 GHz 8.8 dBi Yagi Antenna
http://directionalantennas.com/yagi_antennas.htm
Azimuth Pattern
•
•
•
•
Elevation Pattern
8.8 dBi directional antenna
2.4 GHz band
Used in WLAN or WISP applications
Indoors or outside
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Flat Panel
•
•
physically in the shape of a square or rectangle
quite directional
http://www.frontierpc.com/
ProductImages/Large/1010892869.jpg
Elevation Pattern
Azimuth Pattern
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Single Patch Antenna
http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html
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4x4 Patch Array Antenna
http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html
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4x4 Patch Array Antenna
Azimuth Plane
Patterns
Elevation Plane
Patterns
http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html
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Parabolic Dish
•
•
Extremely high gain and sharp directivity
• Very directional
Use a reflective parabola dish
• to focus all received electromagnetic waves on the antenna to a
single point
http://www.wlan.org.uk/astra%2060cms%20dish.jpg
Azimuth Pattern
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Microstrip
http://www.emtalk.com/mwt_mpa.htm
• Manufactured with PCB traces on actual
PCB boards
• Very small and lightweight
• Small output power
• microstrip antennas are not well suited for
wideband communications systems
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Notebook Antenna
(a) Wireless LAN antenna, AUX (black)
(b) Wireless WAN antenna, AUX (blue)
(c) Camera cable (some models)
(d) Wireless WAN antenna, MAIN (red)
(e) Wireless LAN antenna, MAIN (gray)
(f) MIMO antenna (white)
Lenovo: ThinkPad
www-307.ibm.com/.../site.wss/MIGR-71582.html
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WLAN Service Antenna for 2.4GHz
"HOT SPOT 16"
• 16dBi
• Omnidirectional horizontal polarisation
www.wlan.org.uk/antenna-page.html
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Sector antenna
(mechanically tilted down by 5 degrees)
Coverage Gaps
from Elevation Plane Nulls
Reduced Coverage Gaps
from a Sector Antenna with "Null Fill"
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Poor Man's WiFi
http://askyourpc.com/media/blogs/a/images/wifi_projects.jpg
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Cantenna
• Use a tin can as a waveguide
• Use a short wire soldered on an N
connector as a probe for coaxial-cable-to
waveguide transition
• It is a directional antenna
• Useful for short to medium distance pointto-point links
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Cantenna
http://www.ipodtouchfans.com/forums/imgcache/26917.png
IWING Project
http://iwing.cpe.ku.ac.th
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Building a Cantenna
L
@2.44 GHz:
 = 12.2 cm.
0.60  ≤ D ≤ 0.75  7.3 cm. ≤ D ≤ 9.2 cm.
=wavelength
G=guide wavelength
L ≥ 0.75 G
L ≥ 56.40 cm
S = 0.25 G
S = 3.05 cm
Antenna Gain 10 -14 dBi
Beam-width

60 degrees
Summarized from
http://www.vias.org/wirelessnetw/wndw_06_08_04.html
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