Transcript Yagi Antenna Design for Animal Tracking

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
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.
Whole System Overview
Antenna 1
RF switch
matrix
Antenna 6
Data
Display
Signal
Processing
(this project only involves the dashed part)
Filters
Amplifiers
Objectives
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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.
The Yagi Antenna
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Invented in the 1920s by Hidetsugu Yagi
and Shintaro Uda, two Japanese university
professors
A type of multielement array
Components of a Yagi
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Center boom
• Can be metallic, but requires correction to
elements
Components of a Yagi
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One driven element
• Connected to source
• Only active element
Components of a Yagi
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One reflector
• Positioned behind the driven element
• Reflects radiation in desired direction
Components of a Yagi
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N ≥ 0 directors
• Placed in front of driven element
• Directs radiation in desired direction
• Focuses radiation pattern
Components of a Yagi
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Matching device
• Matches impedance
of antenna to a
desired value
• T match
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Matches impedance
of antenna to 50Ω
Balanced matching
device
• Reduces pattern
distortion
Components of a Yagi
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Balun
• Connects BALanced antenna to
UNbalanced coax
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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
Components of a Yagi
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1:1 balun
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

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
Design Requirements
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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 50Ω coax cable
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Yagi Design
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Used Quickyagi to design antenna
Used Yagicad to determine matching
parameters
Yagi Design
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E plane field
Yagi Design
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H plane field
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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 λ
Correction ≈
29%*1.25” ≈ 9mm
Percent of Boom Diameter Which Must be Added to Element Length
Yagi Design
Yagi Construction
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Materials
• Boom
6’ long aluminum tube
 1.25” outer diameter
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• Elements
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3/16” diameter aluminum (copper for driven
element) rods
• Plastic insulators and push-nut retaining
rings to attach elements to boom
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)
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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
Example show standard kit
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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
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

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
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Extended center
conductor of a coax cable
of length λ/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
Testing – Impedance Background
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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
Testing – Impedance Procedure
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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
Testing – Impedance
Procedure2
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5. Couldn’t 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 GammaMatch, 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.
Testing – Impedance
Procedure3
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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
Testing – Impedance SWR
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Standing Wave
Ratio near 1
demonstrates
matching working
well (very little
reflected):
SWR Formula: |r| =
(SWR-1)/(SWR+1)
Antenna – Power Reflection (Log Scale)
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Spike at 302 MHz –
desired
Spike larger than 10 dB
No other major
spikes
Works according to
design
Testing – Radiation Tests
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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
Testing – Radiation Procedure1
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1. Connect monopole to port2
2. Keep Yagi stationary on top
of 2 chair backs – step back
so human body doesn’t
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.
Testing – Radiation Procedure2
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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.
Testing – Radiation Procedure3
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Test if height of monopole relative to
Yagi affects results:
• Conclusion: not significantly.
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Test if distance of monopole relative
to Yagi affects results:
• Conclusion: beyond 1 meter, it seems to
stay the same.
Testing – Results Power Spectrum
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Spike at 302 MHz,
as designed.
No other
comparable spikes.
Worked as
expected
Testing – Results Radiation Pattern
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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:
Testing – Results Radiation Pattern
2
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0 degree to 180 degree sweep.
Somewhat different from expected results but general
shape similar.
Discrepancies attributed to non-ideal testing
conditions and reflections.
Obstacles and Challenges 1
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Graduate Student Advisor departed
• The person we worked most with and assisted us with
direction and guidance.
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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 wouldn’t work, didn’t match the specific
project specifications and functions.
• Professor George Swenson said too difficult for us to do
in our meeting with him.
Obstacles and Challenges 2
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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.
Obstacles and Challenges 3
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Calibration
• Only one calibration set found and needed
someone to calibrate for us since owner of
calibration set didn’t 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 couldn’t proceed without it.
Obstacles and Challenges 4
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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.
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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.
Acknowledgements
ECE Professor Bernhard
 ECE Graduate student Brian Herting
 Professor Larkin of the INHS
 345 TA Chirantan Mukhopadhyay
 ECE Professor George Swenson
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