february 2005copyright 2005 all rights reserved1 antennas (1 september, 2006)

February 2005 Copyright 2005 All Rights Reserved 1

Antennas (1 September, 2006)


Explain the types of wireless LAN antennas and how/when to use them

Describe the various wireless LAN accessories and where they are used

ObjectivesUpon completion of this chapter you will be able to:


External Antenna Classifications

Omni-directional AntennaMast mount omni

Pillar mount omni

Ground plane omni

Ceiling mount omni

Highly- directional AntennaParabolic dish

Grid antenna

Semi-directional antennaPatch Antenna

Panel Antenna

Sectorized antenna

Yagi Antenna

http://www.fab-corp.com


Omni-directional AntennaMast mount omni

Blade omni

PC Card integrated omni

Pillar mount omni

Ground plane omni

Ceiling mount (blister) omni



Omni-directional Antennas

The omni-directional Dipole antenna is the most common WLAN antenna.

The radiating element is about 1 inch long for 2.4 Ghz and even shorter for the 5 Ghz frequency.

As the wavelength becomes higher the antenna becomes shorter.

It radiates energy equally around the antenna axis- 360 degrees.

However it dos not radiate along the length of the antenna hence the radiation pattern is in the shape of a doughnut.

Anything radiating in all directions equally (the sun) is called and isotropic radiator.

The gain of an antenna is referenced to an isotropic Radiator.

The higher the gain the more horizontally squeezed the doughnut.


Omni-directional Antenna Radiation Pattern


Dipole/Omni Antenna

Omni Ceiling Mount Antenna

Omni Pillar Mount Antenna

Omni Ceiling (Blister) Mount Antenna

Omni Blade Antenna


Omni-directional Usage

Omni Coverage

Used when coverage in all directions is required.

Typically in a

Pt-multipoint link

warehouse

hotspot

Tradeshow

Airport


Omni-directional Antennas

2.4 Gz 10 dBi Omni-Directional Antenna

2.4 Gz 5 dB Magnetic Mount Omni Antenna


Cantenna Waveguide Antenna

http://www.cantenna.com/


5.2 dBi Omni-directional Antenna

Vertical Pattern


5.2 dBi Omni-directional Antenna Contd

Frequency Range 2.4-2.83 GHz

VSWR Less than 2:1, 1.5:1 Nominal

Gain 5.2dBi

Polarization Vertical

Azimuth 3dB BW Omnidirectional 360 degrees

Elevations Plan (3dB BW) 50 degrees

Antenna Connector RP-TNC

Dimensions (H x W) 11.5 x 1.125 in.

Mounting Mast mount—indoor/outdoor


Semi-directional antenna Patch Antenna

Panel Antenna

Sectorized antenna

Yagi Antenna



Semi-directional antenna

Semi-directional antenna radiate in a cylindrical coverage pattern

Used for: Connecting buildings

A long corridor

in the corner of a large indoor space

rail yards,

retail stores

Manufacturing facilities

Golf Courses, etc

They are most often used for short distances (2-3 miles) to bridge two buildings.


Patch Antenna

Patch Antenna


Patch Antenna Contd


VSWR 2:1 Max, 1.5:1 Nominal

Gain 8.5dBi


Azimuth 3dB BW 60 degrees

Elevations 3dB BW 55 degrees


Dimensions (H x W x D) 4.88 x 4.88 x .6 in.

Mounting Wall Mount


Semi-directional Antenna Radiation Pattern

Directional Patch Antenna

Main lobe

Back Lobe


2.4 Gz 13.5 dBi Radome Yagi

Vertical Pattern

Horizontal Pattern


2.4 Gz 13.5 dBi Radome Yagi


VSWR Less than 2:1, 1.5:1 Nominal

Gain 13.5dBi

Front to Back Ratio Greater than 30 dB


Azimuth 3dB BW 30 degrees

Elevations 3dB BW 25 degrees


Dimensions (H x W) 18 x 3 in.

Wind Rating 110 MPH

Mounting Mast/Wall Mount


Semi-directional Antenna Radiation Pattern

Directional Yagi Antenna

Main lobeSide Lobe

Back Lobe

Beamwidth

Beamwidth is calculated by measuring the number of degrees off-axis where the beam drops to -1/2 its strength at the zero-degree position.


Azimuth and Elevation Charts

Azimuth

Elevation


Point-to-Point Wireless Bridge Link


Highly- Directional AntennaParabolic dish

Grid antenna



Highly-directional antenna

Highly-directional antenna radiate in a cylindrical coverage pattern that is highly flattened. Not used for communicating with clients.

Used for Pt-to-Pt communication links

Blast through obstructions

Must be accurately aligned.

They are most often used for long distances (35 miles) for pt-to-pt communication.


2.4 Ghz 21 dBi Parabolic Dish Antenna


2.4 Ghz 21 dBi Parabolic Dish Antenna


VSWR Less than 1.8:1, 15:1 Nominal

Power 5 watts

Gain 21dBi

Front to Back Ratio Greater than 25 dB

Maximum Side Lobe -17 dB


Azimuth 3dB BW 12.4 degrees

Elevation 3dB BW 12.4 degrees


Dimensions (H x W) 24 x 15.5 in.

Wind Rating 110 MPH

Mounting Mast Mount


2.4 Gz 19 dBi Reflector Grid Antenna

Grid Dish Parabolic Antenna (2400 to 2485 MHz Operation)

15dBi, 19dBi and 24dBi models Rugged and Weatherproof Ultra Low Wind Loading and Low Visual Impact Vertical or Horizontal Polarization 2.4GHz Wireless LAN Applications • Point to Point Backhaul 802.11b and 802.11g Wireless • Client Antennas


Line of sight

Line of Sight

The RF Line of Sight (LOS) is an apparent straight line between the transmitter and receiver.

It is apparent because of changes in RF direction due to refraction, diffraction and reflection.

RF LOS is affected by blockage of the Fresnel Zone.


Line of sight


Fresnel Zone

The Fresnel Zone occupies a series of concentric circles around the RF LOS.

Objects in the Fresnel Zone can diffract or reflect the RF wave away from receiver thereby changing the RF LOS.

The formula to calculate the "60 percent unobstructed radius" is:

√

d/4fr = 43.3 x

Typically 20%-40% Fresnel Zone blockage introduces little or no interference.

Attempt to Design the link with 0% blockage. If this is not possible then allow no more than 20% blockage of the Fresnel Zone.

Line of Sight


Line of sight

There are several options to establish or improve the line of sight: Raise the antenna mounting point on the existing structure Build a new structure, i.e. radio tower, which is tall enough to mount the antenna Increase the height of an existing tower Locate a different mounting point, i.e. building or tower, for the antenna Cut down problem trees


Earth BulgeLine of Sight

The earth's horizon can obstruct the Fresnel Zone if the distance between antennas is greater than 7 miles.

The formula for calculating the additional antenna height needed to correct for the communication links greater than 7 miles is:

H=D2/8

The formula for calculating the minimum antenna height for communication links over 7 miles is:

D2/8√

D/4F) +H = (43.3 x


Diverse Antennas



Diverse Antennas

Diverse antennas are used to overcome multipath distortion (multipath fading).

This uses two antennas separated by at least one wavelength.

Multipath distortion occurs at the receiver when the wavelength travels multipaths from the transmitter to the receiver.

The reflected wave travels farther than the desired wave arriving later in time.

The reflected wave travels farther and loses more RF energy than the direct wave.

The signal will lose energy when reflected.


Multipath Fading

Multipath

Reception

Distortion


Diverse Antenna Switch

Diverse antennas include two antennas that are connected to an RF switch which in turn is connected to the receiver.

The receiver switches between antennas sampling the preamble.

It then selects the best antenna for receiving the signal.

The transmitter then uses the same signal for transmission.


Antenna's have four fundamental concepts: Polarization: The orientation of the Electric component of the

electro-magnetic field. Gain: A measure of the increase in power. Direction: The shape of the radiated transmission pattern. Free Space Path Loss: RF signal loss due to transmission

distance.

Antenna Concepts


Polarization The Radio wave is made up of an oscillating electro-magnetic field composed of two planes:

H-Plane: The Magnetic plane is created perpendicular to the antenna.

E-Plane: The Electric plane is created parallel to the antenna and defines the orientation of the radio waves radiated from the antenna.

Vertical polarization has the E-Plane perpendicular to the earth. Most WLAN antennas are vertically polarized.

Horizontal Polarization has the E-Plan horizontal to the earth.

H-Plane

E-PlaneAntenna


Different Polarized Antennas

Vertically Polarized Antenna Horizontally Polarized Antenna


Gain and Direction Gain is the increase in energy that an antenna appears to add to the RF Signal.

An antenna has passive gain – they do not increase the power input to them.

Real antennas reshape the radiation pattern by simply redirecting the energy through reflection – think of a flashlight that has the ability to change its beamwidth.

It provides more energy in one direction and less in another.

As the Antenna gain increases the angle of radiation decreases:

This provides greater coverage distance but

Less coverage angle


Beamwidth

Side View Top View

Side View Top View

Less energy in one direction More energy in one direction

Wider Beamwidth Smaller Beamwidth


Beamwidth Contd

Narrowing or focusing antenna beams increase or decrease the antenna's gain – dBi.

The beamwidth is composed of a vertical and a horizontal element.

DirectionalAntenna

HorizontalBeamwidth

Ver

tical

Bea

mw

idth


Gain and Direction Contd

Basic Antenna gain is rated in comparison to an Isotropic radiator.

An isotropic radiator is a theoretical construct that radiates equally in all direction simultaneously.

The Antenna's gain is measured in dBi – decibels relative to an Isotropic radiator.

The dBi rating is used to compare the power level of a given antenna to the theoretical isotropic radiator.

For example, an isotropic radiator has a gain of 0 dBi whereas a dipole is rated at 2.14 dBi.


Free Space loss Free Space loss is the loss incurred by an RF signal as it travels over distance.

The signal disperses (broadens) over distance.

The power decrease is inversely proportional to the distance traveled and proportional to the signal wavelength.

The 6dB rule states

A 6dB increase in EIRP doubles the range.

A 6dB decrease in EIRP cuts the range in half.


End of Lecture

february 2005copyright 2005 all rights reserved1 antennas (1 september, 2006)

Documents

antenna axis

rights reserved5

rights reservedobjectives

dbi omnidirectional

common wlan antenna

nominal gain

db bw omnidirectional

types of wireless lan