9 - Antenna dan Propagasi.ppt

  Antenna and Propagation

• 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)

  Signal and Antenna Concepts

• 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 office
• – Complex-multiple semi-directional antennas

  Active and Passive Gain

• 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

  Passive Gain

• Focusing isotropic energy in a specific pattern
• Created by the design of the antenna
• – Uses the magnify glass concept

  Active Gain

• Providing an external power source
• – Amplifier – High gain transmitters
Azimuth and Elevation Charts

• Charts help you “see” how antennas focus energy
• – Polar charts or antenna radiation envelopes

  Azimuth and Elevation Charts

• In either chart, the antenna is placed at the middle of the chart.
• – Azimuth chart = H-plane = top-down view
• – Elevation chart = E-plane = side view
• Like casting a shadow with your hand – Shape is same, but size grows with power.

  Antenna Types

• Antennas not only amplify transmitted signal, they amplify received signal

  Omnidirectional Antennas

• Common on many access Points
• – Dipole
>Rubber
• Bagel shaped transmission
• Limited vertical coverage
• Wide horizontal coverage
• Low gain antennas are usually 2.14dB
• – Higher gain is more elongated (long and thin)

  Low Gain Omni-directional Antenna The omni antenna is the most commonly used antenna type _{High Gain Omni-directional Antenna  Gain of signal along the coverage pattern along a flat plane.}  Provides 360º horizontal _{ Omni-directional antennas are along the vertical plane} horizontal plane means less signal also known as dipoles.

  Antennas

• Antennas are most effective when the element is an even fraction or a multiple of the wavelength (λ) – ¼, ½, 1, 2, etc.
• Used in multipoint environments
• – Indoor Access Point – Building to multiple building coverage
• Beware of higher gain limiting the vertical coverage

Semidirectional Antennas

• Designed to direct the signal in a specific direction
• – Point to point-outdoors about a mile
• – Down hallways
• Three types
• – Planar Type
• Patch • Panel
• – Yagi

  Semidirectional Antennas

• Multiple planar antennas can be used to cover multiple aisles
• – Libraries, Warehouses, Retail, etc
• Yagi antennas are like old TV antennas
• – However, each element is fitted for wireless wavelengths
• Even fraction or multiple of wavelength

  Patch _{Semi-directional Antennas directional antenna types on Sector are the primary semi-}  Patch, Panel, Yagi and _{have 180º or less of  Semi-directional antennas} the market today _width horizontal and vertical beam _{ Primary coverage uses} include: _{Wireless ISPs Hallways/Corridors}

  P _{PTP & PTMP Bridging} atc h _{Multiple semi-directional} antennas can be combined Highly Directional Antennas

• For Point to Point
• – Generally between two buildings
• Focused, narrow beamwidth
• Two main types
• – Parabolic Dish – Grid Antenna
• Since they are used outdoors, wind loading is an issue
• – Since they have narrow beamwidth, the wind can push them out of direction

Highly Directional Antennas

• Highly focused energy
• Most common type - parabolic

  Phased Array Antennas

• Multiple antennas connected to a signal processor
• Different antennas can be fed different phases
• – Able 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

  Sector Antennas

• 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

  Line of Sight

• The “line” from source to destination
• – Visual LOS is not important on Wireless networks
• RF line of sight is
• – Mostly for outdoor point to point connections
• – Should be unobstructed

Maintaining Clear Communications

• Visual line of sight
• RF line of sight
• Fresnel zone

  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
• – more than 40% will make link unrealiable
• – Keep it to less than 20%

  Fresnel Zone

• No Fresnel math on test
• 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
• – Or at certain distances
• Important for keeping out obstructions

Fresnel Zone

• Don’t mistake smaller beamwidth for smaller Fresnel zone
• Fresnel zone is affected by the frequency fo the transmission, not the antenna

Earth Bulge

• For longer Point to Point links-More than 7 miles
• Important to calculate height requirements for towers

  Antenna Polarization

• 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
• – 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

  Antenna Diversity

• Helps compensate for multipath
• An AP has multiple antennas
• – Compares the signal from each antenna and choose the best signal
• – Done frame bu frame
• 802.11n uses switched diversity
• – Signal with the best amplitude is used
• – Also known as received diversity
• Can also use measurement to choose the transmit antenna

  Antenna Diversity

• 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
Multiple In Multiple Out (MIMO)

• More sophisticated type of antenna diversity
• Takes advantage of multipath
• Uses Space Time Coding
• – Send multiple signals simultaneously

  Voltage Standing Wave Ratio (VSWR)

• 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 tyou are connecting
• – Cable to transmitter

  Voltage Standing Wave Ratio (VSWR)

• Ratio of energy reflected is the voltage reflection coefficient
• – 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=V

  /V

  max min Voltage Standing Wave Ratio (VSWR)

• Higher the return loss, the less broadcast power
• – ^{Return voltage can also damage the transmitter}

  Signal Loss

• The goal when connecting the antenna to transmitter is to reduce signal loss
• Must pay attention to devices used
• – Cables and connectors

Antenna Mounting

• Placement • Mounting • Appropriate Use • Orientation and alignment
• Safety • Maintenance

  Placement

• Correct 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
• Outdoors-Watch the Fresnel Zone

  Mounting

• Outdoors
• – Masts or towers
• Indoors
• – Wall or ceiling
• Often want to hide or camouflage for aesthetics

  Appropriate Use

• Indoor vs. Outdoor • Although they look the same, they are designed for correct temperature and environment

Orientation and Alignment

• Pay attention to horizontal vs. vertical alignment
• Polarization can make the difference between being able to communicate or not

  Safety

• Be careful
• RF health and safety courses
• – FCC and OSHA regulations
• If installing on a tower, pole, etc-get a professional.

  Maintenance

• Preventative and diagnostic
• Don’t just set and forget
• – Especially not outdoors
• Outdoors you need to be aware of wind and water damage
• – Wind
• Properly mount
• – Water

  Antenna Accessories

• All devices attached in the RF system need to be checked for
• – Frequency response
• – Impedance – VSWR
• – Maximum input power
• – Insertion loss

  Cables

• Choose the correct cable based on technology, frequency, etc
• – Some cables can’t be used with some frequencies
• – Match the impedance
• – Calculate the signal loss
• Different for different frequencies
• – Purchase pre-cut of hire a professional
• You want to measure loss in the connections

  Connectors

• 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

  RF Connectors

• Join cables and devices together
• – AP to antenna
• – Antenna to cable
• – Cable to cable – Etc.

  Splitters

• 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

  Amplifiers

• For active gain
• Unidirectional
• – transmit only
• Bi-directional
• – Transmit and receive
• Fixed output
• – Generate a signal equal to that of the amplifier
• Fixed Gain
• – Adds amplifier to transmitter power

  Attenuators

• In cases where you need to limit the range or power
• – If the minimum power setting isn’t small enough

  Lightning Arrestors

• Protect from power surges due to nearby strikes
• – Direct strike will fry it
• Protects the devices behind it on the circuit

  Lightening Arrestors _{ An in-line RF device that} Lightning Arrestors _{ Dissipates static ground} must be connected to Earth _{Does not prevent equipment loss in antennas are struck,  When objects near RF} electricity in the air

  Lightning Arrestors Grounding Rod and Wires

• Important to have a common ground
• – Properly sunk copper rod and connectors
• – Tinned copper wire to connect tower legs