1. Antenna Basics Module 3A
Jerry Bernardini
Community College of Rhode Island
CCRI J. Bernardini

2. Presentation Reference Material
The California Regional Consortium for Engineering Advances in Technological Education (CREATE) project
CWNA Certified Wireless Network Administration Official Study Guide
(PWO-104), David Coleman, David Westcott, 2009, Chapter-1
Cisco Wireless technology
4/17/2017
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3. Antenna Principles
A theoretical isotropic antenna has a perfect 360º vertical and horizontal beamwidth
The Isotropic antenna the a reference for all antennas (dBi)
Antennas are symmetrical: A receiving antenna has the same characteristics as a transmitter
Antennas have gain in particular directions
Direction other than the main intended radiation pattern, are typically related to the main lobe gain
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4. Different Antennas
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5. Key Antenna Terms Plane H (H-Horizontal) Plane E(E-Elevation) Lobes
Directional
Omnidirectional
Beamwidth
Bandwidth
Polarization
Vertical (Elevation)
Horizontal (Azimuth)
Diversity
VSWR
Antenna Accessories
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6. Antenna Gains
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7. Antenna Characteristics
Main beam is the region around the direction of maximum radiation The main beam is centered at 90 degrees
Sidelobes are smaller beams that are away from the main beam. Radiate in directions other than the main beam and can never be completely eliminated.
Half Power Beamwidth (HPBW) is the angular separation in which the magnitude of the radiation pattern decrease by 50% (or -3 dB) from the peak of the main beam.
Null to Null Beamwidth. the angular separation from which the magnitude of the radiation pattern decreases to zero (negative infinity dB) away from the main beam.
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8. H-Plane-Azimuth 0o
Beamwidth -3dB
270o
90o
180o
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9. Beamwidths
0 dB
-3dB
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10. Polar Pattern Analysis
50o Beam
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11. Dipole H and E Planes
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12. 5.8 dBi Omnidirectional Antenna,
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13. Typical Dipole Antenna Beam Pattern
Starting from an Isotropic antenna energy lobes are ‘pushed in’ from the top and bottom
Higher gain
Smaller vertical beamwidth
Larger horizontal lobe
Typical dipole pattern
Side View
(Vertical Pattern)
Top View
(Horizontal Pattern)
New Pattern (with Gain)
Vertical Beamwidth
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14. 2.4 GHz Omni-Directional Antennas
2 dBi Dipole "Standard Rubber Duck"
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15. Rubber Ducky Antenna Construction
Each half of the dipole is a 1/4 wavelength, with the length corrected based on the velocity of the coax being used. Assuming a centre frequency for b of 2.441GHz, a 1/4 wavelength in free space is 30.7mm.
Length of the metal casing is approx 24mm, with a total length of 50mm.
Thin wire whip protruding from the top of the metal casing is approx 26mm
Metal casing is a "decoupler", and is typically used to tune the antenna, by moving the decoupler up and down to vary the VSWR .
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16. High Gain Omni-Directionals
More coverage area in a circular pattern
Energy level directly above or below the antenna will become lower
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17. 2.4 GHz Omni-Directional Antennas
5.2 dBi Mast Mount Vertical
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18. 2.4 GHz Omni-Directional Antennas
5.2 dBi Pillar Mount Diversity
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19. 2.4 GHz Diversity Omni-Directional Antennas
2 dBi Diversity Omni-Directional Ceiling Mount
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20. 2.4 GHz Omni-Directional Antennas
12 dBi Omni-Directional (Outdoor only)
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21. 2.4 GHz Diversity Antennas
6.5 dBi Diversity Patch Wall Mount – 55 degree
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22. 2.4 GHz Directional Antennas (cont.)
6 dBi Patch Antenna – 65 degree
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23. 2.4 GHz Directional Antennas (cont.)
8.5 dBi Patch Antenna – 60 degree
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24. 2.4 GHz 13.5 dBi Yagi Antenna
– 25 degree Beamwidth
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25. 2.4 GHz Directional Antennas (cont.)
21 dBi Parabolic Dish Antenna – 12 degree
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26. Antenna Polarization E-Plane is parallel to the antenna
H-Plane is perpendicular to the antenna
Horizontal Polarization – the Electric field is parallel to the ground
Vertical Polarization – the Electric field is perpendicular to the ground
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27. FCC Rules 2.4 GHz EIRP Point-to-Multipoint Point-to-Point
FCC allows increasing the gain of an antenna/cable system if the transmitter power is reduced below 30 dBm in a 1:1 ratio
Reduce Transmit Power below maximum of 30 dBm by 1 dBm and increase antenna/cable system gain by 1dBi
Point-to-Point
Maximum of 36 dBm EIRP
Installations – 30 dBm maximum transmitter power with 6 dBi in gain attributed to antenna and cable combination
FCC allows exceeding the 36 dBm EIRP in Point-to-Point installations using the 3:1 rule
Reduce Transmit Power below maximum of 30 dBm by 1 dBm and increase antenna/cable system gain by 3 dBi
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28. Voltage Standing Wave Ratio (VSWR)
A measure of the change in impedance to an AC signal.
Ratio of the Maximum Voltage to Minimum Voltage in an RF system.
Typical Values: : 1 to :1 (1:1 Ideal system; impossible to obtain)
Measure of the amount of energy sent to the antenna that reflects back to the transmitter.
Too large a VSWR will reflect too much energy back to the transmitter and damage the transmitter
Output of Transmitter must match Cable , which matches Antenna impedance
Return Loss – Ratio of Reflected voltage to Transmitter voltage in dB. Ideally this should be small
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29. VSWR Table CCRI J. Bernardini TRANS. RETURN POWER VSWR LOSS REFL. :1
TRANS.
RETURN
POWER
VSWR
LOSS
REFL. :1
[dB]
[%]
1.00
0,00 ∞
100
1.20
1.58
20.83
0.036
99.17
0.83
1.30
2.28
17.69
0.075
98.30
1.70
1.50
3.52
13.98
0.177
96.00
4.00
1.80
5.11
10.88
0.37
91.84
8.16
2.00
6.02
9.54
0.512
88.90
11.10
12.00
4.44
1.94
64.00
36.00
5.00
14.00
2.55
55.60
44.40
6.00
15.60
2.92
3.1
49.00
51.00
10.00
20.00
1.74
4.81
33.10
66.90
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30. Impedance Matching Effects
When the impedances are matched –Half of the source power is delivered to the load and half is dissipated within the (equivalent) generator as heat
For receiving antenna, half the power captured is lost as heat in the antenna elements, the other part being reradiated (scattered) back into space
When the antenna impedance is not matched to the transmitter output impedance (or to the receiver input impedance) or to the transmission line between them, impedance-matching devices must be used for maximum power transfer.
-impedance-matching devices are used They are usually narrow-band
Transmission lines often have significant losses
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31. Antenna Diversity
Receiver selects the stronger antenna signal compensating for multipath
Frame by frame antenna sampling to determine strongest signal
Transmitting occurs on the previous strong-signal antenna =Transmit Diversity
Not all access points have Trasmitter Diversity
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32. Multiple-Input Multiple-Output (MIMO)
A sophisticated form of antenna diversity
Multipath signals are Space Time Coding (STC) processed to improve receiver performance
IEEE n employs MIMO
Not specified with a, b,g
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33. Antenna Path Considerations
Radio line of sight
Height of Earth bulge
Fresnel Zone Radius
Height of Obstacles
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34. Line of Sight The following obstructions might obscure a visual link:
Topographic features, such as mountains
Curvature of the Earth
Buildings and other man-made objects
Trees
Line of sight!
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35. Longer Distances
Line of Sight disappears at 6 miles (9.7 Km) due to the earth curve
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36. Fresnel Zone
Fresnel Zone
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37. CCRI J. Bernardini

38. Improving Fresnel Effect
Raise the antenna
New structure
Existing structure
Different mounting point
Remove trees
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39. Site to Site Fresnel Zone
Antenna Height
Fresnel zone consideration
Line-of-Sight over 25 miles (40 Km) hard to implement
Antenna Height (Value “H”)
Total Distance
60% (Value “F”)
Earth Curvature (Value “C”)
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40. Antenna Alignment
Line of Sight
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41. Antenna Installation
Towers and antennas may require permits and must meet local regulations
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42. Grounding Antenna towers must be ground to protect from lightning
Grounding Rods (6 ft r
Antenna
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43. 5 GHz Integrated Antenna
Innovative 5 GHz Combo Antenna:
Wall Mount: Fold antenna flat against access point housing for 6 dBi gain patch antenna
Ceiling Mount: Fold antenna out at a 90° angle for 5 dBi gain omni antenna
In 6 dBi patch position
In 5 dBi omni position
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44. 2.4 GHz Accessories
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45. RP-TNC Connectors
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46. Lightning Arrestor
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47. Lightning Arrestor
Designed to protect LAN devices from static electricity and lightning surges that travel on coax transmission lines
RP-TNC connectors used on all Cisco Antennas
To Antenna
Lug
Lockwasher
Nut
Ground Wire
From RF Device
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