Oct. 23, 2006Oct. 23, 2006Midterm Marked. Midterm Marked. – Average: 73%. 6 below, 9 aboveAverage: 73%. 6 below, 9 above– Answer Key posted: Answer Key posted:

http://people.okanagan.bc.ca/dwilliams/coursehttp://people.okanagan.bc.ca/dwilliams/courses/nten216/Tests/NTEN216_Midterm1WithAnss/nten216/Tests/NTEN216_Midterm1WithAnswers2006.pdfwers2006.pdf

Assignment #4 Assignment #4 – will be posted tonight will be posted tonight – Due next Monday (Oct. 30)Due next Monday (Oct. 30)

Antenna lab today – who brought a can?Antenna lab today – who brought a can?Sector Antennas, propagation paths, free Sector Antennas, propagation paths, free space loss, link budgetsspace loss, link budgets

Sector AntennasSector Antennas

Generate “Pie Slice” radiation patternsGenerate “Pie Slice” radiation patterns

““Pie Slice” width depends on particular Pie Slice” width depends on particular antennaantenna

Because of predictability of slice, multiple Because of predictability of slice, multiple antennas may be mounted together to antennas may be mounted together to give larger coverage areagive larger coverage area

E.g. want 270° of coverage, but have only E.g. want 270° of coverage, but have only 90° sector antennas, what do you do.90° sector antennas, what do you do.

Sector Antenna CharacteristicsSector Antenna Characteristics

Gain: 10-21dBi.Gain: 10-21dBi.– A 90° sector antenna can still have variable A 90° sector antenna can still have variable

gain by changing the vertical patterngain by changing the vertical pattern

Beamwidth: Depends on Pie Slice sizeBeamwidth: Depends on Pie Slice size

Polarization: linearPolarization: linear

Bandwidth:Bandwidth:– Effective from Effective from

Sector Antenna Radiation PatternSector Antenna Radiation Pattern

Increase coverage area by joining three 120° Increase coverage area by joining three 120° antennas together.antennas together.

Omnidirectional in horizontal plane, controllable Omnidirectional in horizontal plane, controllable in vertical plane.in vertical plane.

AntennaAntenna GainGain

(dBi)(dBi)

BeamBeamwidthwidth

PolariPolarizationzation

BandBandwidthwidth

Lower Lower FF

Upper Upper FF

λλ/2 Dipole/2 Dipole 22 80x36080x360 LinearLinear 10%10% NoneNone 6GHz6GHz

λλ/4 /4 MonopoleMonopole

2-62-6 45x36045x360 LinearLinear 10%10% NoneNone NoneNone

ParabolicParabolic 20-3020-30 1-101-10 LinearLinear 33%33% 400MHz400MHz 13GHz13GHz

YagiYagi 5-155-15 50x5050x50 LinearLinear 5%5% 50MHz50MHz 2GHz2GHz

PatchPatch 8-188-18 VariesVaries LinearLinear

ArrayArray variesvaries VariesVaries LinearLinear 10MHz10MHz 10GHz10GHz

SectorSector 8-218-21 VariesVaries LinearLinear

ReviewReviewWhat are lobes and nulls?What are lobes and nulls?If you have a right handed circularly polarized If you have a right handed circularly polarized transmission antenna, what is the best kind of transmission antenna, what is the best kind of antenna to use as the reception antenna?antenna to use as the reception antenna?If the gain of an antenna is 5dBi for If the gain of an antenna is 5dBi for transmission, and its beamwidth for transmission transmission, and its beamwidth for transmission is 90°x45°, what would the gain and beamwidth is 90°x45°, what would the gain and beamwidth be if it was used for reception? What is this be if it was used for reception? What is this principle called?principle called?A 1 watt signal is input to an antenna, but A 1 watt signal is input to an antenna, but 200mW is reflected. The gain of the antenna is 200mW is reflected. The gain of the antenna is 10dBi, and the loss of power due to resistance is 10dBi, and the loss of power due to resistance is 50mW. What is the efficiency of this antenna?50mW. What is the efficiency of this antenna?

ReviewReview

What happens if there is an impedance What happens if there is an impedance mismatch between the antenna, and the cable mismatch between the antenna, and the cable coming into the antenna?coming into the antenna?

The center frequency of an antenna is The center frequency of an antenna is 104.7MHz, and at 104.7MHz it radiates 50 Watts 104.7MHz, and at 104.7MHz it radiates 50 Watts of power. If it radiates a 100MHz signal, it can of power. If it radiates a 100MHz signal, it can only output 12.5W of power, and at 110MHz, it only output 12.5W of power, and at 110MHz, it can only output 12.5W of power. What is the can only output 12.5W of power. What is the bandwidth of this antenna?bandwidth of this antenna?

ReviewReview

In terms of In terms of directionality, what directionality, what kind of antenna is this kind of antenna is this ??

What are the What are the horizontal and vertical horizontal and vertical beamwidths?beamwidths?

In the vertical plane, In the vertical plane, what is the signal what is the signal strength at 45° if the strength at 45° if the strength at 90° is strength at 90° is 50mW?50mW?

ReviewReviewDescribe at least two ways to provide full Describe at least two ways to provide full wireless coverage to a large rectangularly wireless coverage to a large rectangularly shaped warehouse. Explain the types of shaped warehouse. Explain the types of antennas you would use and why.antennas you would use and why.

If you have need for long distance point to If you have need for long distance point to point communications, what kind of point communications, what kind of antenna would you use.antenna would you use.

What would you use a Yagi antenna for?What would you use a Yagi antenna for?

Wave PropagationWave Propagation

Ground (Surface) Wave PropagationGround (Surface) Wave Propagation

Sky Wave PropagationSky Wave Propagation

Free Space Wave PropagationFree Space Wave Propagation– Line of SightLine of Sight– Fresnel ZonesFresnel Zones– Free Space LossFree Space Loss– Link BudgetLink Budget

Ground Wave PropagationGround Wave Propagation

EM waves that travel over the Earth’s EM waves that travel over the Earth’s surface surface – Best at low frequencies, over conductive Best at low frequencies, over conductive

surfaces surfaces

30kHz – 3MHz follow curvature of Earth30kHz – 3MHz follow curvature of Earth

Sky Wave PropagationSky Wave Propagation

Transmission of RF signals by bouncing Transmission of RF signals by bouncing them off the ionospherethem off the ionosphereAllows for VERY long distance Allows for VERY long distance communication – thousands of kms in communication – thousands of kms in ideal circumstancesideal circumstancesRole of ionosphereRole of ionosphere– Ionized air 50+ km above Earth’s SurfaceIonized air 50+ km above Earth’s Surface– Reflects 3kHz – 30MHzReflects 3kHz – 30MHz– Multihop propagationMultihop propagation

Ionosphere OpacityIonosphere Opacity

Most opaque for RF below 30MHzMost opaque for RF below 30MHzOpacity can changeOpacity can change– Time of day – the solar wind pushes ionosphere in, so Time of day – the solar wind pushes ionosphere in, so

lower layer disappears at nightlower layer disappears at night– sunspotssunspots

Space Wave PropagationSpace Wave Propagation

Propagation of RF signal through free Propagation of RF signal through free spacespace

Line of sight and reflected wave Line of sight and reflected wave propagationpropagation

RF “line of sight” slightly different than RF “line of sight” slightly different than visual line of sightvisual line of sight– RF signal diffractionRF signal diffraction– Fresnel ZoneFresnel Zone

Fresnel ZonesFresnel Zones““Zones” through which RF signals propagateZones” through which RF signals propagate– Numbered starting at 1Numbered starting at 1

Odd numbered zones are constructiveOdd numbered zones are constructive

Even numbered zones are destructiveEven numbered zones are destructive

Fresnel Zone ClearanceFresnel Zone Clearance

First Fresnel Zone must be mostly clear of First Fresnel Zone must be mostly clear of obstacles for successful signal propagationobstacles for successful signal propagation– Rule of thumb: 60% clearRule of thumb: 60% clear

Minimum unobstructed radius:Minimum unobstructed radius:

r = 54.77 x sqrt(d/4f)r = 54.77 x sqrt(d/4f)

fdr 477.54

Free Space LossFree Space Loss

RF signal weakens as it propagates away RF signal weakens as it propagates away from sourcefrom sourceOverall power remains same, area it Overall power remains same, area it covers increasecovers increase– Actual decrease is Power/unit areaActual decrease is Power/unit area

Free Space Path Loss:Free Space Path Loss:(4(4ππR/R/λλ))2 2 = (4= (4ππRf/c)Rf/c)22 or or

20log(R) + 20log(f) - 14820log(R) + 20log(f) - 148– R squared. f squared why?R squared. f squared why?

Link Budget

• System analysis accounting for all sources of signal loss and gain

)()()()(Pr dBLossesdBGainsdBmPdBm txx

• Gains: tx antenna, rx antenna, amplifiers• Losses: cables, connectors, free space, polarization• Fade Margin

– Account for changing conditions– Add 10 to 30 dB to budget