Yagi Antenna Design for Animal Tracking Applications

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Yagi Antenna Design for Animal Tracking
Applications

• Minh Phan, Andrew Price, Denny Tu
• University of Illinois at Urbana-Champaign
• Department of Electrical Engineering
• Senior Design, ECE345
• May 2, 2003

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Motivation for Project

• The current method used to track tagged animals
  requires scientists to manually drive around with
  portable antennas tracking the particular
  animal(s) they are interested in. This method is
  very time consuming and produces small amounts of
  data. In order to facilitate an automatic
  tracking system, antennas to receive the signals
  from the tags must be designed, built and tested.

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Whole System Overview
Antenna 1
RF switch matrix
Antenna 6
Amplifiers
Filters
Signal Processing
Data Display
(this project only involves the dashed part)
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Objectives

• Design a yagi antenna using simulation software.
• Build the antenna according to designed
  specifications.
• Test antenna and verify it performs as expected.
• Design an RF switch matrix to switch 6 antenna
  feed lines to 1 or 2 amplifiers in the down
  conversion module.

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The Yagi Antenna

• Invented in the 1920s by Hidetsugu Yagi and
  Shintaro Uda, two Japanese university professors
• A type of multielement array

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Components of a Yagi

• Center boom
• Can be metallic, but requires correction to
  elements

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Components of a Yagi

• One driven element
• Connected to source
• Only active element

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Components of a Yagi

• One reflector
• Positioned behind the driven element
• Reflects radiation in desired direction

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Components of a Yagi

• N 0 directors
• Placed in front of driven element
• Directs radiation in desired direction
• Focuses radiation pattern

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Components of a Yagi

• Matching device
• Matches impedance of antenna to a desired value
• T match
• Matches impedance of antenna to 50O
• Balanced matching device
• Reduces pattern distortion

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Components of a Yagi

• Balun
• Connects BALanced antenna to UNbalanced coax
• Prevents common-mode currents on the outer
  surface of the outer conductor of the coax feed
  which can affect the pattern and other properties
• Can also perform an impedance transformation

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Components of a Yagi

• 11 balun

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How a Yagi Works

• Driven element radiates
• Radiation induces currents in reflector and
  directors
• These currents in turn re-radiate
• Adjusting the length of elements, their diameters
  and relative positions along the boom adjusts the
  radiated fields

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How a Yagi Works

• The previously mentioned parameters are adjusted
  in such a way as to make the fields
  constructively interfere in one direction, and
  destructively interfere in the opposite direction
• This creates the typical directional radiation
  pattern

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How a Yagi Works
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Design Requirements

• Half-power beam width 60
• In order to ensure adequate coverage of areas
  between antennas
• As large a gain as possible
• As large a front-to-back ratio as possible
• Connect to a 50O coax cable

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Yagi Design

• Used Quickyagi to design antenna
• Used Yagicad to determine matching parameters

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Yagi Design

• E plane field

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Yagi Design

• H plane field

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Yagi Design

• A conducting boom will be used to build the
  antenna, so a correction to the lengths of the
  elements is required to prevent pattern
  distortions
• Boom diameter 1.25 .032 ?
• Correction 291.25 9mm

Percent of Boom Diameter Which Must be Added to
Element Length
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Yagi Construction

• Materials
• Boom
• 6 long aluminum tube
• 1.25 outer diameter
• Elements
• 3/16 diameter aluminum (copper for driven
  element) rods
• Plastic insulators and push-nut retaining rings
  to attach elements to boom

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Yagi Construction

• Holes in boom drilled by computer controlled
  machine in the ECE machine shop
• Elements cut using band saw in ECE machine shop
• T-match bars and balun soldered on

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Antenna-Network Analyzer (NA)

• First step One port (port1) calibrate by use SOLT
  (short, open, load, and through) standard kit. So
  port 1 will be connect to Yagi antenna.
• From NA we should see at corrected calibration by
  display Smitch chart such as Open, short, and
  load located as where it should be.
• The frequency range from 100mhz to 1Ghz

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Example show standard kit

• Using a coax cable 50 ohms hookup with a adapter
  then we connected each of components as disired
  from stanadard kit short, open, and load. Let
  take a look at the Load

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Connect through NA

• Port1 have been done calibrate then connect yagi
  antenna at this time we will try get it match 50
  ohms.
• Port2 connect monopole with coax cable 50 ohms

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Monopole Antenna - Purpose

• Not in our original plan.
• For testing, needed constant transmitter for yagi
  antenna to receive signal.
• Difficult to find/use natural transmitters
  operating at 302MHz (band of our yagi is narrow).
• Can use easily in lab.

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Monopole Antenna - Transmitter

• Extended center conductor of a coax cable of
  length ?/4 25cm to transmit at 302 MHz
• Ground plane aluminum foil covered cardboard
  base
• Ground plane 50cm x 50cm, equidistant from
  center conductor on all sides
• Copper tape to connect outer conductor of coaxial
  cable to ground plane

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Testing Impedance Background

• Ideal 50 ohms real, 0 ohms reactance
• Impedance Matching is what the calibration was
  needed for.
• Theory T Match use 0.2m copper wire, arm length
  2.7cm, spacing 2.1cm, capacitance 16pF

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Testing Impedance Procedure

• 1. Connect antenna port1
• 2. Direct antenna facing out open lab window in
  order to minimize reflection (accuracy)
• 3. Read impedance using Smith Chart and marker at
  302MHz
• 4. Adjust connectors, test different lengths

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Testing Impedance Procedure2

• 5. Couldnt achieve close to desired impedance.
• 6. Hypothesis Balun may be at fault, so remove
  it.
• 7. More testing, still no positive results.
• 8. Get additional wire, according to theoretical
  predictions.
• 9. Silver wire very difficult to solder.
• 10. Test T-Match and Gamma-Match, still not
  desired results.
• 11. Replace with 14mm copper wire, bend, test.
• 12. Discover wiring incorrect.
• 13. Correct wiring and attach balun once more
  because needed to match currents.

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Testing Impedance Procedure3

• 14. More testing and adjusting, Gamma-Match,
  T-Match
• 15. Recheck and redo the solder connections
• 16. Adjust height, distance, angle, etc.
• Finally, achieve results close to ideal goal
• 51.1 real, 2.3 reactance, 97.5 get through
• 47.5 real, -13.5 reactance, 86 get through

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Testing Impedance SWR

• Standing Wave Ratio near 1 demonstrates matching
  working well (very little reflected)
• SWR Formula r (SWR-1)/(SWR1)

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Antenna Power Reflection (Log Scale)

• Spike at 302 MHz desired
• Spike larger than -10 dB
• No other major spikes
• Works according to design

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Testing Radiation Tests

• Calibration not essential, normalize
• H-plane is horizontal, E-plane vertical
• Direction of poles have to align
• Minimum distance 1-2m between transmitter and
  receiver
• Radiation pattern ideally symmetric
• 2 Procedures
• Keep Yagi receiver stationary and rotate monopole
  transmitter around it at set degree intervals
• Keep monopole stationary and turn the Yagi in a
  circle

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Testing Radiation Procedure1

• 1. Connect monopole to port2
• 2. Keep Yagi stationary on top of 2 chair backs
  step back so human body doesnt adversely affect
  results.
• 3. Hold monopole as far away as possible.
• 4. Starting at 0 degrees, take measurements and
  proceed in 10 degree increments up to 180
  degrees.
• 5. Keep monopole level with Yagi.
• 6. Plot points in Matlab and compare with ideal
  results obtained from simulation.
• 7. Repeat several times for accuracy.

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Testing Radiation Procedure2

• 1. Locate monopole antenna next to window
  (minimize reflection) and keep stationary.
• 2. Set Yagi on chair backs facing the monopole.
• 3. Keep monopole and Yagi level.
• 4. Take measurements starting at 0 degrees and
  going to 180 degrees.
• 5. After each measurement, turn Yagi antenna 10
  degrees, make stationary, step away.
• 6. Repeat several times.
• 7. Analyze results.

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Testing Radiation Procedure3

• Test if height of monopole relative to Yagi
  affects results
• Conclusion not significantly.
• Test if distance of monopole relative to Yagi
  affects results
• Conclusion beyond 1 meter, it seems to stay the
  same.

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Testing Results Power Spectrum

• Spike at 302 MHz, as designed.
• No other comparable spikes.
• Worked as expected

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Testing Results Radiation Pattern

• Similar to ideal results simulated using computer
  software
• Front to Back Ratio -30.6 dB/-39.1 dB
• Graph shows front half of radiation pattern

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Testing Results Radiation Pattern 2

• 0 degree to 180 degree sweep.
• Somewhat different from expected results but
  general shape similar.
• Discrepancies attributed to non-ideal testing
  conditions and reflections.

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Obstacles and Challenges 1

• Graduate Student Advisor departed
• The person we worked most with and assisted us
  with direction and guidance.
• Switch Matrix
• Part of original plan take input from 6
  antennas, switching between all 6 within 15ms so
  as to not miss any data. Produce 1 output that
  computer program others working on decodes to
  find location of animals.
• Many fruitless hours searching and planning.
• Ideas that wouldnt work, didnt match the
  specific project specifications and functions.
• Professor George Swenson said too difficult for
  us to do in our meeting with him.

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Obstacles and Challenges 2

• Suitable Testing Environment
• Ideal isolated, open area without conflicting
  signals but with necessary equipment and
  accessibility.
• Antenna testing lab on top floor of Everitt
  unsuitable for our antenna bandwidth.
• ECE345 Lab turned out to be most viable option
  but many people working around us disruptions,
  conflicting signals, reflections, human
  interference.

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Obstacles and Challenges 3

• Calibration
• Only one calibration set found and needed someone
  to calibrate for us since owner of calibration
  set didnt want to leave it with us.
• Unable to save calibration so another group using
  or turning off network analyzer means we need to
  calibrate again.
• Owner of calibration set not always available and
  we couldnt proceed without it.

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Obstacles and Challenges 4

• Impedance Matching
• Very unstable, the slightest touch makes a big
  change.
• Varies a great deal sometimes one location
  gives a value, another time the same location
  gives a totally different value.
• Human touch/proximity affects results
  significantly.
• Miscellaneous
• Faulty cables
• Find sufficient cables and connectors to be able
  to test using a single network analyzer while
  maintaining sufficient distance between Yagi and
  monopole.

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Acknowledgements

• ECE Professor Bernhard
• ECE Graduate student Brian Herting
• Professor Larkin of the INHS
• 345 TA Chirantan Mukhopadhyay
• ECE Professor George Swenson