1. Antenna Fundamentals
Lecture 4

2. Objectives
List some of the characteristics of RF antenna transmissions
Describe the different types of antennas

3. Antenna principles

4. Adjusting Antennas: Antenna Types (continued)
Figure 10-17: Azimuth and elevation pattern

5. H Plane

6. V Plane

7. Beam width

8. Beam width

9. Types of Antenna

10. Antenna types

11. Patch antenna

12. Yagi antenna

13. Radiation pattern semi directional antenna

14. Adjusting Antennas: RF Transmissions
May need to adjust antennas in response to firmware upgrades or changes in environment
May require reorientation or repositioning
May require new type of antenna
Radio frequency link between sender and receiver consists of three basic elements:
Effective transmitting power
Propagation loss
Effective receiving sensibility

15. Adjusting Antennas: RF Transmissions (continued)
Figure 10-14: Radio frequency link

16. Adjusting Antennas: RF Transmissions (continued)
Link budget: Calculation to determine if signal will have proper strength when it reaches link’s end
Required information:
Antenna gain
Free space path loss
Frequency of the link
Loss of each connector at the specified frequency
Number of connectors used
Path length
Power of the transmitter

17. Adjusting Antennas: RF Transmissions (continued)
Link budget (continued):
Required information (continued):
Total length of transmission cable and loss per unit length at specified frequency
For proper WLAN performance, link budget must be greater than zero
System operating margin (SOM)
Good WLAN link has link budget over 6 dB
Fade margin: Difference between strongest RF signal in an area and weakest signal that a receiver can process

18. Link budget

19. Example (Specs)

20. Adjusting Antennas: RF Transmissions (continued)
Attenuation (loss): Negative difference in amplitude between RF signals
Absorption
Reflection
Scattering
Refraction
Diffraction
Voltage Standing Wave Ratio

21. Adjusting Antennas: Antenna Types
Rod antenna: Antenna typically used on a WLAN
Omnidirectional
360 degree radiation pattern
Transmission pattern focused along horizontal plane
Increasing length creates “tighter” 360-degree beam
Sectorized antenna: “Cuts” standard 360-degree pattern into four quarters
Each quarter has own transmitter and antenna
Can adjust power to each sector independently

22. Adjusting Antennas: Antenna Types (continued)
Figure 10-15: Rod antenna pattern

23. Omni Directional Antennas

24. Omni directional antennas

25. Adjusting Antennas: Antenna Types (continued)
Panel antenna: Typically used in outdoor areas
“Tight” beamwidth
Phase shifter: Allows wireless device to use a beam steering antenna to improve receiver performance
Direct transmit antenna pattern to target

26. Phased array antenna
: Incorporates network of phase shifters, allowing antenna to be pointed electronically in microseconds,
Without physical realignment or movement

27. Adjusting Antennas: Antenna Types (continued)
Radiation pattern emitting from antennas travels in three-dimensional “donut” form
Azimuth and elevation planes
Antenna Accessories:
Transmission problem can be resolved by adding “accessories” to antenna system
Provide additional power to the antenna, decrease power when necessary, or provide additional functionality

28. The bigger the better

29. Adjusting Antennas: Antenna Types (continued)
Figure 10-17: Azimuth and elevation pattern

30. Adjusting Antennas: RF Amplifier
Increases amplitude of an RF signal
Signal gain
Unidirectional amplifier: Increases RF signal level before injected into transmitting antenna
Bidirectional amplifier: Boosts RF signal before injected into device containing the antenna
Most amplifiers for APs are bidirectional

31. Adjusting Antennas: RF Attenuators
Decrease RF signal
May be used when gain of an antenna did not match power output of an AP
Fixed-loss attenuators: Limit RF power by set amount
Variable-loss attenuators: Allow user to set amount of loss
Fixed-loss attenuators are the only type permitted by the FCC for WLAN systems

32. Attenuators

33. Amplifiers

34. Adjusting Antennas: Cables and Connectors
Basic rules for selecting cables and connectors:
Ensure connector matches electrical capacity of cable and device, along with type and gender of connector
Use high-quality connectors and cables
Make cable lengths as short as possible
Make sure cables match electrical capacity of connectors
Try to purchase pre-manufactured cables
Use splitters sparingly

35. Splitters

36. Lightning

37. Adjusting Antennas: Lightning Arrestor
Antennas can inadvertently pick up high electrical discharges
From nearby lightning strike or contact with high-voltage electrical source
Lightning Arrestor: Limits amplitude and disturbing interference voltages by channeling them to ground
Designed to be installed between antenna cable and wireless device
One end (3) connects to antenna
Other end (2) connects to wireless device
Ground lug (1) connects to grounded cable

38. Adjusting Antennas: Lightning Arrestor (continued)
Figure 10-18: Lightning arrestor

39. RP TCN Lightning arrestor

40. Ethernet lightning arrestors

41. Grounding arrestors

42. Lightining

43. Isolating with fiber

44. Protection with fiber

45. Summary (continued)
An antenna is a copper wire or similar device that has one end in the air and the other end connected to the ground or a grounded device
There are a variety of characteristics of RF antenna transmissions that play a role in properly designing and setting up a WLAN

46. AP 1200 initial configuration sample
config t
hostname "raul"
interface dot11radio 0
ip address
no ip route-cache
channel "Channel 1-11"
ssid "raul"
authentication open
guest-mode
End
write

47. Lab 3
2.5, and 3.5 of Text Book