active and passive gain azimuth and elevation charts (antenna radiation envelopes) interpreting...
Post on 28-Dec-2015
244 Views
Preview:
TRANSCRIPT
Active and Passive Gain Azimuth and elevation charts (antenna radiation
envelopes) Interpreting polar charts Beamwidth Antenna types
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.Simple-omni-directional in middle of officeComplex-multiple semi-directional antennas
Pg 107
Measurements of the increase in signal from the Antenna (EIRP) 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 antennaUses the magnify glass concept
Providing an external power sourceAmplifierHigh gain transmitters
Charts help you “see” how antennas focus energyPolar charts or antenna radiation envelopes
Pg 109
In either chart, the antenna is placed at the middle of the chart.Azimuth chart = H-plane = top-down viewElevation chart = E-plane = side view
Like casting a shadow with your handShape is same, but size grows with power.
Pg 109
Easy to misinterpretThe chart shows the DECIBEL mapping of
coverage Each line 5 dB!!
Normalized charts appear very different
Pg 110
Easy to misinterpretThe 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 isMeasured both horizontally and verticallyTo the point where the signal decreases by
half power (-3dB)
Pg 113
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
Omnidirectional 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 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 on many access PointsDipole
Rubber duck
Bagel shaped transmission Wide horizontal coverage Limited vertical coverage Low gain antennas are usually 2.14dB
Higher gain is more elongated
Pg 116
High Gain Omni-directional Antenna
Low Gain Omni-directional Antenna
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.
The omni antenna is the most commonly used antenna type
Antennas are most effective when the element is an even fraction or a multiple of the wavelength (λ)¼, ½, 1, 2, etc.
Higher gain antennas are often made by stacking dipole antennas
Used in multipoint environments Indoor Access PointBuilding to multiple building coverage
Beware of higher gain limiting the vertical coverage
Pg 117
Designed to direct the signal in a specific directionPoint to point-outdoors about a mileDown hallways
Three typesPlanar Type
Patch Panel
Yagi
Pg 118
Multiple planar antennas can be used to cover multiple aislesLibraries, Warehouses, Retail, etc
Yagi antennas are like old TV antennasHowever, each element is fitted for wireless
wavelengths 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
PatchSemi-directional
Antennas
Patch, Panel, Yagi and Sector are the primary semi-directional antenna types on the market today Semi-directional antennas have 180º or less of horizontal and vertical beam width Primary coverage uses include:
Hallways/CorridorsWireless ISPsPTP & PTMP Bridging
Multiple semi-directional antennas can be combined into an array to provide omni-directional coverage.
Patch
For Point to PointGenerally between two buildings
Focused, narrow beamwidth Two main types
Parabolic DishGrid Antenna
Since they are used outdoors, wind loading is an issueSince 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 phasesAble to create very directed beams
Usually regulated differently Not common in 802.11
802.11n has a PHY specification that supports it Smart antenna technology
Pg 123
Specialized high gain, semidirectional antenna
Multiple antennas with limited back lobeEach 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 “line” from source to destinationVisual LOS is not important on Wireless
networks RF 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 transmissionsmore than 40% will make link unrealiableKeep 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 middleOr 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 diversityMultiple 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
Compares the signal from each antenna and choose the best signal
802.11n uses switched diversitySignal with the best amplitude is usedAlso 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 directionsThat defeats the purpose
Usually a single radio with multiple connectionsCommon 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 signalWhen 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
connectingCable to transmitterCable to antenna
Pg 133
Ratio of energy reflected is the voltage reflection coefficientReturn Loss
Ideally, there is no mismatchA 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 usedCables and connectors
Pg 134
Placement Mounting Appropriate Use Orientation and alignment Safety Maintenance
Pg 134
Correct placement for type of antennaOmnidirectional toward centerSemi-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 ZonePg 135
OutdoorsMasts or towers
IndoorsWall 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 damageWind
Properly mountWater
Cold-shrink tubing, sealant, drip loops
Pg 137
All devices attached in the RF system need to be checked forFrequency response ImpedanceVSWRMaximum input power Insertion loss
Pg 137
Choose the correct cable based on technology, frequency, etcSome cables can’t be used with some
frequenciesMatch the impedanceCalculate the signal loss
Different for different frequenciesPurchase 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 antennasPigtail adapters get around this requirement
Be careful of exceeding FCC regulations
Pg 139
Join cables and devices togetherAP to antennaAntenna to cableCable to cableEtc.
Signal splitter, RF splitter, Power Splitter Used when you need the signal to go to
more than one locationMultiple antennas
Will cause loss and degradation of signalPower monitoring
Pg 139
For active gain Unidirectional
transmit only Bi-directional
Transmit and receive Fixed output
Generate a signal equal to that of the amplifier
Fixed GainAdds 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 strikesDirect strike will fry it
Protects the devices behind it on the circuit
Pg 141
Does not prevent equipment loss in cases of direct lightning strikes!
Lightning Arrestors
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 groundProperly sunk copper rod and connectorsTinned 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.
top related