Transcript Semi-directional Antennas






Active and Passive Gain
Azimuth and elevation charts (antenna radiation envelopes)
Interpreting polar charts
Beamwidth
Antenna types
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Omnidirectional antennas
Semidirectional antennas
Highly directional antennas
Phased array antennas
Sector antennas
Visual line of sight
RF line of sight
Fresnel zone
Earth bulge
Antenna polarization
Antenna diversity
Multiple-input multiple-output (MIMO)

Understand passive and active gain


Understand how antennas provide passive gain and how
transceivers and amplifiers provide active gain.
Know the different categories and types of
antennas, how they radiate signals, and what
type of environment they are used in.

Make sure you know the three main categories of
antennas and the different types of antennas. know the
similarities and differences between them, and
understand when and why you would use one antenna
over another. Make sure that you understand azimuth
and elevation charts, beamwidth, antenna polarization,
and antenna diversity.

Fully understand the Fresnel zone.


Make sure you understand all of the issues and variables
involved with installing point-to-point communications. You
are not required to memorize the Fresnel zone or earth
bulge formulas; however, you will need to know the
principles regarding these topics and when and why you
would use the formulas.
Understand the concerns associated with connecting
and installing antennas and the antenna accessories.

Every cable, connector, and device between the transceiver
and the antenna affects the signal that gets radiated from
the antenna. Understand which devices provide gain and
which devices provide loss. Understand what vSWR is and
what values are good or bad. know the different antenna
accessories, what they do, and why and when you would
use them.
 Signal
must be radiate with enough power so
that is will be understood by the receiver
 Antenna installation will have a great effect.
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Simple-omni-directional in middle of office
Complex-multiple semi-directional antennas
Pg 107
 Measurements
of the increase in signal from
the Antenna (EIRP)
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If gain is from an amplifier or increased power at
the transmitter-it is ACTIVE Gain
If from shaping or focusing the power with an
antenna,-PASSIVE Gain
 Passive
gain from focusing existing Power
 Active Gain by adding more power
Pg 107
 Focusing
isotropic energy in a specific
pattern
 Created by the design of the antenna
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Uses the magnify glass concept
 Providing
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an external power source
Amplifier
High gain transmitters
 Charts
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help you “see” how antennas focus energy
Polar charts or antenna radiation envelopes
Pg 109
 In
either chart, the antenna is placed at the
middle of the chart.
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Azimuth chart = H-plane = top-down view
Elevation chart = E-plane = side view
 Like
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casting a shadow with your hand
Shape is same, but size grows with power.
Pg 109
 Easy
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to misinterpret
The chart shows the DECIBEL mapping of
coverage
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Each line 5 dB!!
 Normalized
charts appear very different
Pg 110
 Easy

to misinterpret
The chart shows the DECIBEL mapping of coverage

Each line 5 dB!!
 Normalized
charts appear very different
Pg 110
 The
measure of how broad or narrow the
focus of an antenna is
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Measured both horizontally and vertically
To the point where the signal decreases by half
power (-3dB)
Pg 113
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First determine the scale of the polar chart. On this
chart, you can see that the solid circles represent
the –10, –20, and –30 dB lines, and the dotted
circles therefore represent the –5, –15, and –25 dB
line
Now to determine the beamwidth of this antenna,
frst locate the point on the chart where the
antenna signal is the strongest. In this example, the
signal is strongest where the number 1 arrow is
pointing. Move along the antenna pattern away
from the peak signal (as shown by the two number 2
arrows) until you reach the point where the
antenna pattern is 3 dB closer to the center of the
diagram (as shown by the two number 3 arrows).
This is why you needed to know the scale of the
chart first. Draw a line from each of these points to
the middle of the polar chart (as shown by the dark
dotted lines) and measure the distance in degrees
between these lines to calculate the beamwidth of
the antenna. In this example, the beamwidth of this
antenna is about 30 degrees.
Pg 113
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Omnidirectional
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Semidirectional
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Omnidirectional antennas radiate RF in a fashion similar to the way a table or foor
lamp radiates light. They are designed to provide general coverage in all directions.
Semidirectional antennas radiate RF in a fashion similar to the way a wall sconce
radiates light away from the wall or the way a street lamp shines light down on a
street or a parking lot, providing a directional light across a large area.
Highly directional

Highly directional antennas radiate RF in a fashion similar to the way a spotlight
focuses light on a fag or a sign.
Pg 115
 Antennas
not only amplify transmitted signal,
they amplify received signal
Pg 115
 Common
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on many access Points
Dipole
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Rubber duck
 Bagel
shaped transmission
 Wide horizontal coverage
 Limited vertical coverage
 Low gain antennas are usually 2.14dB
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Higher gain is more elongated
Pg 116
Low Gain Omni-directional Antenna
The omni antenna is the most commonly used antenna type
 Provides 360º horizontal
coverage pattern along a flat
plane.
 Gain of signal along the
horizontal plane means less signal
along the vertical plane
 Omni-directional antennas are
also known as dipoles.
High Gain Omni-directional Antenna
 Antennas
are most effective when the
element is an even fraction or a multiple
of the wavelength (λ)
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¼, ½, 1, 2, etc.
 Higher
gain antennas are often made by
stacking dipole antennas
 Used in multipoint environments
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Indoor Access Point
Building to multiple building coverage
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Beware of higher gain limiting the vertical coverage
Pg 117
 Designed
to direct the signal in a specific
direction
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Point to point-outdoors about a mile
Down hallways
 Three
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Planar Type
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types
Patch
Panel
Yagi
Pg 118
 Multiple
planar antennas can be used to
cover multiple aisles
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Libraries, Warehouses, Retail, etc
 Yagi
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antennas are like old TV antennas
However, each element is fitted for wireless
wavelengths
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Even fraction or multiple of wavelength
Pg 119
 Also
good on walls
 Most have limited side lobe and vertical and
can be pointed down for coverage
Pg 121
Patch
Semi-directional Antennas
Patch
 Patch, Panel, Yagi and
Sector are the primary semidirectional antenna types on
the market today
 Semi-directional antennas
have 180º or less of
horizontal and vertical beam
width
 Primary coverage uses
include:
Hallways/Corridors
Wireless ISPs
PTP & PTMP Bridging
Multiple semi-directional
antennas can be combined
into an array to provide
omni-directional coverage.
 For

Point to Point
Generally between two buildings
 Focused,
narrow beamwidth
 Two main types
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Parabolic Dish
Grid Antenna
 Since
they are used outdoors, wind
loading is an issue
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Since they have narrow beamwidth, the wind
can push them out of direction
Pg 121
 Highly
focused energy
 Most common type - parabolic
 Multiple
antennas connected to a signal
processor
 Different antennas can be fed different
phases
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Able to create very directed beams
 Usually
regulated differently
 Not common in 802.11
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802.11n has a PHY specification that supports
it
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Smart antenna technology
Pg 123
 Specialized
high gain, semidirectional
antenna
 Multiple antennas with limited back lobe

Each antenna can be on its on its own transceiver
 Usually
set up to provide 360 degree
coverage
 Used extensively in cellular phone systems
Pg 123
 The
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Visual LOS is not important on Wireless networks
 RF
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
“line” from source to destination
line of sight is
Mostly for outdoor point to point connections
Should be unobstructed
Pg 124
 Visual
line of sight
 RF line of sight
 Fresnel zone
 Football
shaped area around the “LOS”
 Actually multiple zones surrounding the main
line of sight
 If first Fresnel zone is obstructed, it will
affect the transmissions
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more than 40% will make link unrealiable
Keep it to less than 20%
Pg 125
 You
need to understand how the calculations
will affect placement when designing a point
to point.
 Can calculate the size of the zone in middle
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Or at certain distances
 Important
for keeping out obstructions
Pg 125
 Don’t
mistake smaller beamwidth for smaller
Fresnel zone
 Fresnel zone is affected by the frequency of
the transmission, not the antenna
Pg 128
 For
longer Point to Point links-More than 7
miles
 Important to calculate height requirements
for towers
Pg 128
 Alignment
of the antenna can affect
polarization
 Doesn’t matter if it is horizontal or
vertical, both transmitter and receiver
need to be the same way
 Most systems have antenna diversity
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Multiple antennas (more than one wavelength
away)
 If
the Received Signal Level (RSL) is 10 to
15 dB less than expected, you may be
linking to a side lobe
Pg 130
 Helps
compensate for multipath
 An AP has multiple antennas
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Compares the signal from each antenna and choose
the best signal
 802.11n
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uses switched diversity
Signal with the best amplitude is used
Also known as received diversity
 Can
also use measurement to choose the
transmit antenna
Pg 130
 Don’t
put the antennas in different locations or
point in different directions

That defeats the purpose
 Usually

a single radio with multiple connections
Common inside laptops
Pg 130
 More
sophisticated type of antenna diversity
 Takes advantage of multipath
 Uses Space Time Coding

Send multiple signals simultaneously
Pg 132
 Measure
of the change in impedances to an
AC signal

When there is a difference or mismatch in
impedance between devices in a RF system
 Forward
Energy is reflected backward to the
transmitter
 Usually at points where you are connecting


Cable to transmitter
Cable to antenna
Pg 133
 Ratio
of energy reflected is the voltage
reflection coefficient
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Return Loss
 Ideally,

there is no mismatch
A matched cable, 0 ratio, infinite return loss
 VSWR
is a measure between the maximum
voltage and minimum voltage
 VSWR=Vmax/Vmin
Pg 133
 Higher
the return loss, the less broadcast
power
 Return voltage can also damage the transmitter
Pg 133
 The
goal when connecting the antenna to
transmitter is to reduce signal loss
 Must pay attention to devices used
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Cables and connectors
Pg 134
 Placement
 Mounting
 Appropriate
Use
 Orientation and alignment
 Safety
 Maintenance
Pg 134
 Correct
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placement for type of antenna
Omnidirectional toward center
Semi-direction at edge, pointed toward center
 Pay
attention to vertical and horizontal
coverage
 Also, power levels
Too high a power will provide an overlarge
coverage area

Security risk
 Outdoors-Watch
the Fresnel Zone
Pg 135
 Outdoors
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Masts or towers
 Indoors
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Wall or ceiling
 Often
want to hide or camouflage for
aesthetics
Pg 135
 Indoor
vs. Outdoor
 Although they look the same, they are
designed for correct temperature and
environment
Pg 136
 Pay
attention to horizontal vs. vertical
alignment
 Polarization can make the difference
between being able to communicate or not
Pg 136
 Be
careful
 RF health and safety courses

FCC and OSHA regulations
 If
installing on a tower, pole, etc-get a
professional.
Pg 135
 Preventative
and diagnostic
 Don’t just set and forget

Especially not outdoors
 Outdoors
you need to be aware of wind and
water damage
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Wind
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Properly mount
Water
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Cold-shrink tubing, sealant, drip loops
Pg 137
 All
devices attached in the RF system need to
be checked for
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Frequency response
Impedance
VSWR
Maximum input power
Insertion loss
Pg 137
 Choose
the correct cable based on
technology, frequency, etc

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
Some cables can’t be used with some frequencies
Match the impedance
Calculate the signal loss
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
Different for different frequencies
Purchase pre-cut of hire a professional

You want to measure loss in the connections
Pg 139
 FCC
has mandated that manufacturers use
unique connectors to limit the ability to use
noncertified antennas

Pigtail adapters get around this requirement
 Be
careful of exceeding FCC regulations
Pg 139
 Join
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
cables and devices together
AP to antenna
Antenna to cable
Cable to cable
Etc.
 Signal
splitter, RF splitter, Power Splitter
 Used when you need the signal to go to more
than one location

Multiple antennas


Will cause loss and degradation of signal
Power monitoring
Pg 139
 For
active gain
 Unidirectional

transmit only
 Bi-directional

Transmit and receive
 Fixed

Generate a signal equal to that of the amplifier
 Fixed

output
Gain
Adds amplifier to transmitter power
Pg 140
 In
cases where you need to limit the range or
power

If the minimum power setting isn’t small enough
Pg 140
 Protect
from power surges due to nearby
strikes

Direct strike will fry it
 Protects
the devices behind it on the circuit
Pg 141
Lightning Arrestors
Does not prevent equipment loss in
cases of direct lightning strikes!
 An in-line RF device that
must be connected to Earth
ground
 Dissipates static
electricity in the air
 When objects near RF
antennas are struck,
electrical current is induced
Pg 141
 Important


to have a common ground
Properly sunk copper rod and connectors
Tinned copper wire to connect tower legs
Pg 142

Understand passive and active gain


Understand how antennas provide passive gain and how
transceivers and amplifiers provide active gain.
Know the different categories and types of
antennas, how they radiate signals, and what
type of environment they are used in.

Make sure you know the three main categories of
antennas and the different types of antennas. know the
similarities and differences between them, and
understand when and why you would use one antenna
over another. Make sure that you understand azimuth
and elevation charts, beamwidth, antenna polarization,
and antenna diversity.

Fully understand the Fresnel zone.


Make sure you understand all of the issues and variables
involved with installing point-to-point communications. You
are not required to memorize the Fresnel zone or earth
bulge formulas; however, you will need to know the
principles regarding these topics and when and why you
would use the formulas.
Understand the concerns associated with connecting
and installing antennas and the antenna accessories.

Every cable, connector, and device between the transceiver
and the antenna affects the signal that gets radiated from
the antenna. Understand which devices provide gain and
which devices provide loss. Understand what vSWR is and
what values are good or bad. know the different antenna
accessories, what they do, and why and when you would
use them.