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Antenna

Wireless LANsSep – Dec 2014

รศ. ดร. อนันต์ ผลเพิม่Assoc. 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

LdB = 10 log10( )P1

P2

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Example

http://www.phys.unsw.edu.au/jw/dB.html

• 2 Loudspeakers

• Speaker 1: plays sound with Power P1

• Speaker 2: plays sound with Power P2

•Same environment (frequency, distance)

LdB = 10 log10( )P2

P1

P1P2

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

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For Electrical Power

• Power Gain (GdB)

GdB = 10 log10( ) = 30 dB 1000 W

1 W30 dBW

GdB = 10 log10( ) = 20 dB 100 mW

1 mW20 dBm

• Calculate 0.1W relative to 1 mW (milliwatt)

• Calculate 1000 W relative to 1 W

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http://partnerwiki.cisco.com/ViewWiki/images/2/2b/Omni-vs-direct2-82068.gif

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

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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

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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Modified from: www.ece.nus.edu.sg/.../Teaching/EE4101/index.htm

Antenna Axis

Antenna Radiation Pattern

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)

Antenna Measurement Coordinate System

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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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Polar Grid

http://en.wikipedia.org/wiki/Polar_coordinate_system

Polar

Azimuth (polar angle)

http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html

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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 AntennasPartial 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

• Best used for Tx/Rx from broadside

• Not a directive antenna

Elevation Pattern(Horizontal Pattern)

Azimuth Pattern(Vertical Pattern)

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Generic Dipolehttp://www.engnetbase.com/

Works well 360around antenna

ve3elb.ham-radio.ch/projects.html

Dipole Antenna with 3D Radiation Pattern

19http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html

5.8 dBi Omnidirectional Antenna

20http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html

Directional Antenna

• Main lobe (beam)

• contains max power

• greatest field strength

• bigger than the others lobes21

back lobe

• Beamwidth

• expressed in degrees

http://en.wikipedia.org/

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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

Yagi

23http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html

2.4 GHz 8.8 dBi Yagi Antenna

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Azimuth Pattern Elevation Pattern

• 8.8 dBi directional antenna • 2.4 GHz band • Used in WLAN or WISP applications• Indoors or outside

http://directionalantennas.com/yagi_antennas.htm

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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

Single Patch Antenna

26http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html

4x4 Patch Array Antenna

27http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html

4x4 Patch Array Antenna

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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

• 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

http://www.emtalk.com/mwt_mpa.htm

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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

Sector antenna (mechanically tilted down by 5 degrees)

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Reduced Coverage Gaps from a Sector Antenna with "Null Fill"

Coverage Gaps from Elevation Plane Nulls

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Poor Man's WiFihttp://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 point-to-point links

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Cantenna

http://www.ipodtouchfans.com/forums/imgcache/26917.png

IWING Projecthttp://iwing.cpe.ku.ac.th

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Building a Cantenna

Summarized fromhttp://www.vias.org/wirelessnetw/wndw_06_08_04.html

L

@2.44 GHz: = 12.2 cm.

L ≥ 0.75 G

0.60 ≤ D ≤ 0.75

S = 0.25 G

L ≥ 56.40 cm

S = 3.05 cm

7.3 cm. ≤ D ≤ 9.2 cm.

Antenna Gain 10 -14 dBi

Beam-width 60 degrees=wavelengthG=guide wavelength