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Antenna Fundamentals Lecture 4. 2 Objectives List some of the characteristics of RF antenna transmissions Describe the different types of antennas.

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Presentation on theme: "Antenna Fundamentals Lecture 4. 2 Objectives List some of the characteristics of RF antenna transmissions Describe the different types of antennas."— Presentation transcript:

1 Antenna Fundamentals Lecture 4

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

3 3 Antenna principles

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

5 5 H Plane

6 6 V Plane

7 7 Beam width

8 8

9 9 Types of Antenna

10 10 Antenna types

11 11 Patch antenna

12 12 Yagi antenna

13 13 Radiation pattern semi directional antenna

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

16 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 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 18 Link budget

19 19 Example (Specs)

20 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 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 22 Adjusting Antennas: Antenna Types (continued) Figure 10-15: Rod antenna pattern

23 23 Omni Directional Antennas

24 24 Omni directional antennas

25 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 26 Phased array antenna : Incorporates network of phase shifters, allowing antenna to be pointed electronically in microseconds, Without physical realignment or movement

27 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 28 The bigger the better

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

30 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 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 32 Attenuators

33 33 Amplifiers

34 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 35 Splitters

36 36 Lightning

37 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 38 Adjusting Antennas: Lightning Arrestor (continued) Figure 10-18: Lightning arrestor

39 39 RP TCN Lightning arrestor

40 40 Ethernet lightning arrestors

41 41 Grounding arrestors

42 42 Lightining

43 43 Isolating with fiber

44 44 Protection with fiber

45 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 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 47 Lab 3 2.5, 3. 4 and 3.5 of Text Book


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