antenna concepts © 2001, cisco aironet systems, inc. chapter5-1

Antenna ConceptsAntenna Concepts

© 2001, Cisco Aironet Systems, Inc. Chapter5-1

© 2001, Cisco Systems, Inc. AWLF1.0—Chapter5-3

ObjectivesObjectivesObjectivesObjectives

Upon completion of this chapter, you should be able to:

• Understand how an antenna is used to propagate an RF signal

• Explain what an isotropic antenna is and why it is used as a reference for other antennas

• Identify Cisco Aironet antennas, their coverage patterns, and the proper polarization of each antenna


Cisco Aironet AntennasCisco Aironet AntennasCisco Aironet AntennasCisco Aironet Antennas

FCC requires that ALL antennas sold by a spread spectrum vendor be certified with the radio they are to be sold with

All Cisco Aironet-supplied cables, RF devices and antennas have reverse TNC (RP-TNC) connectors

Cisco Aironet-supplied antennas meet all FCC rules

Wide variety antennas for most applications


Antenna ConceptsAntenna ConceptsAntenna ConceptsAntenna Concepts

Directionality• Omni (360º coverage) directional

• Directional (limited range of coverage)

Gain• Measured in dBi and dBd. (0dBd = 2.14dBi)

• More gain means more coverage - in certain directions

Polarization• Antennas are used in the vertical polarization


Antenna GainAntenna GainAntenna GainAntenna Gain

In life you never get “something for nothing;” the same is true in antenna gain.

If the gain of an antenna goes up, the coverage area or angle goes down.

Coverage areas or radiation patterns are measured in degrees.

These angles are referred to as beamwidth, and have a horizontal and vertical measurement.


Antenna TheoryAntenna TheoryAntenna TheoryAntenna Theory

A theoretical isotropic antenna has a perfect 360º vertical and horizontal beamwidth.

This is a reference for ALL antennas

Side View(Vertical Pattern)

Top View(Horizontal Pattern)


Antenna Theory- DipoleAntenna Theory- DipoleAntenna Theory- DipoleAntenna Theory- Dipole

To obtain omni-directional gain from an isotropic antenna, the energy lobes are ‘pushed in’ from the top and bottom, and forced out in a doughnut type pattern.

The higher the gain, the smaller the vertical beamwidth, and the larger the horizontal lobe area

This is the typical dipole pattern. Gain of a dipoleis 2.14dBi (0dBd)



New Pattern (with Gain)

Vertical Beamwidth


High Gain Omni-DirectionalsHigh Gain Omni-DirectionalsHigh Gain Omni-DirectionalsHigh Gain Omni-Directionals

High gain omni-directional antennas will create more coverage area in away from the antenna, but the energy level directly below the antenna will become lower. Coverage here may be poor.

Area of poor coverage directly under the antenna

Beamwidth


Directional AntennasDirectional AntennasDirectional AntennasDirectional Antennas

For directional antennas the lobes are pushed in a certain direction, causing the energy to be condensed in a particular area.

Very little energy is in the back side of a directional antenna.




FCC Part 15 Antenna FCC Part 15 Antenna RequirementsRequirements

FCC Part 15 Antenna FCC Part 15 Antenna RequirementsRequirements


EIRPEIRPEIRPEIRP

Effective Isotropic Radiated PowerPower Setting dBm

100 mW 20 dBm

50 mW 17 dBm

30 mW 15 dBm20 mW 13 dBm

15 mW 12 dBm

5 mW 7 dBm

1 mW 0 dBm

w/ 6 dBi Patch EIRP

6 dBi 26 dBm

6 dBi 23 dBm

6 dBi 21 dBm6 dBi 19 dBm

6 dBi 18 dBm

6 dBi 13 dBm

6 dBi 6 dBm

Cisco Aironet Cisco Aironet AntennasAntennas

Cisco Aironet Cisco Aironet AntennasAntennas

© 2001, Cisco Systems, Inc. www.cisco.com AWLF 1.0—Chapter5-13


2.4Ghz Omni-Directional 2.4Ghz Omni-Directional AntennasAntennas

2.2dBi Dipole “Standard Rubber Duck”

Cisco Aironet Part # AIR-ANT4941



2.2dBi Ceiling Mount




5.2dBi Ceiling Mount




5.2dBi Mast Mount Vertical




5.2dBi Pillar Mount Diversity




5.2dBi Ground Plane




12dBi Omni Directional (Outdoor only)



2.4Ghz Directional 2.4Ghz Directional AntennasAntennas

3dBi Patch Antenna – 65 degree




6dBi Patch Antenna – 65 degree




8.5dBi Patch Antenna – 55 degree


H Plane

E Plane



13.5dBi Yagi Antenna – 25 degree




21dBi Parabolic Dish Antenna – 12 degree

Cisco Part # AIR-ANT3338


SummarySummarySummarySummary

Upon completion of this chapter you should be able to perform the following tasks:

•How different antennas can affect the propagation of the RF signal

•Compare antenna ratings in dBi vs. dBd

•Assist the customer in choosing the right antenna for their installation


Review QuestionsReview QuestionsReview QuestionsReview Questions

1. A 2.14 dBi antenna is the same as a 3.28 dBd antenna (True/False)?

2. An antenna with more gain is always a better antenna? Why or why not?

3. Ceiling mount antennas are always the best choice for an indoor installation? Why or why not?

4. A higher gain antenna adds more output power to the access point’s output (True/False)?

antenna concepts © 2001, cisco aironet systems, inc. chapter5-1

Documents