body worn/wearable antennas · pdf file2 overview definition and performance metrics •...
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Body Worn/Wearable AntennasPrecision Indoor Personnel Location and Tracking for Emergency Responders
Technology WorkshopWorcester Polytechnic Institute
August 7, 2007
MegaWave Corporation200 Shrewsbury Street, PO Box 614
Boylston, MA 01505Presented: Marshall W. Cross P.E., VP R&D
2
OverviewDefinition and Performance Metrics• Key design considerations
Brief history of Body Worn/Wearable Antenna (BWA) designTypical body worn antenna performance• Computer modeling, performance measurements
Design examplesSummary
3
Definitions and MetricsBody wearable: part of clothing1
Body worn: not part of clothingVHF/UHF: 30-3,000 MHz (λ=10 to 0.1m)Metrics:• Frequency coverage/instantaneous bandwidth • VSWR (50 Ω)• Power gain radiation pattern vs. orientation, position, equipment,
nearby environment• Polarization• Physical survivability• Physical integration – user comfort
1 Hall and Hao, “Antennas and Propagation for Body-Centric Wireless Communications,” Artech House, 2006
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Body Worn Antenna (BWA) Brief Historyand General Considerations
Prior to advent of sophisticated codes, analytical models were developed• Andersen, J., et al, (IEEE Trans. Veh. Tech., Vol. VT-26, #4, Nov.’77) developed
analytical model for VHF radio mounted antennas near body• Krupka, Z., (IEEE T-AP, Vol. AP-16, #2, Mar.’68) developed the notion of body
resonance in the VHF bandMeasured data was obtained
• King et al, (IEEE T-AP, May 1977, pp. 376-379) collected measured data of handset antenna at various locations (head, shoulder and torso) and distances from body
– Gain decreases rapidly with decreased separation from body– Body shields antenna so azimuth patterns are not omnidirectional (this effect is seen at
frequencies as low as 200MHz although F/B ratio is lower at 200MHz)
Computation of on-body performance is complex• Wave impedance that body presents varies with frequency
– At 900MHz, η = 40 + j 6 ohms, lower at lower frequencies– Tends to “short out” E-field antennas located close to the body– Efficiency is reduced
5
REMCOM detailed body model
Computer codes•Finite Difference Time Domain •Transmission Line Matrix Method
Human body model options•Detailed body models
–Include all organ and tissue parameters–Complicated, run time and resource
intensive–Torso non-uniform so difficult to model
conformal antenna (problems found in past with elements intersecting the body tissue)
•Simplified human body–Lossy cylinder with dielectric constant
and conductivity–Based on “SALTY” by Siwiak2
–Rectangular model of body found to give excellent agreement with measurements
Typical Body Worn Antenna Design Approach
body antenna elements
counterpoise
Simplified Body Model
2 Siwiak, “Radiowave Propagation and Antennas for Personal Communications”, Artech House
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MeasurementsFabricate preliminary lab prototypeTest on liquid filled phantom (saltwater or combination of additives3)Measure VSWR, azimuth radiation patterns, gainFabricate and test final antennas on phantom
No head/arms and full body salt water
phantoms
3 K. Ito, “Numerical and Experimental Human Body Phantoms”, IET Seminar, Body Centric Wireless Communications, April 2007.
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Data ComparisonRadiation Patterns
Computed Measured
1250-2500MHz Wearable Antenna on PhantomMeasured Azimuth Patterns
-30-25-20-15-10
-505
100
10 2030
4050
60
70
80
90
100
110
120
130140
150160170
180190200
210220
230
240
250
260
270
280
290
300
310320
330340 350 1250
15001750200022502500
1250-2500MHz Wearable AntennaXFDTD Simulated Azimuth Patterns
-30
-25
-20
-15
-10
-5
0
5
100
10 2030
40
50
60
70
80
90
100
110
120
130
140150
160170180
190200210
220
230
240
250
260
270
280
290
300
310
320330
340 350125015001750200022502500
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Data ComparisonAverage Azimuth Gain
1250-2500MHz BWA on Phantom
-10
-7.5
-5
-2.5
0
2.5
5
1250 1500 1750 2000 2250 2500
Frequency (MHz)
Ave
rage
Azi
mut
h G
ain
(dB
i)
Computed
Measured (Cables & Combiner Loss Included)
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Wearable Antennas – Civilian GarmentExisting frequency bands:
• 136-174, 400-450, 800-900, 1250-2500MHz
• Wideband elements could also be integrated
Casual outer jacket selected for integration
• Other garments possibleAntennas fabricated using conducting fabric on black cotton carrier insert that lies between jacket shell and liningVSWR<2.5:1 in all bands
antenna feed point detail
selected host garment
-30-25-20-15-10
-50
0
30
60
90
120
150
180
210
240
270
300
330
400
425
450
-30-25-20-15-10
-505
010 20 30
4050
60708090100
110120
130140
150160170180
190200210220
230240
250260270280290
300310
320330340350 800
900
1250-2500MHz Wearable Antenna on PhantomMeasured Azimuth Patterns
-30-25-20-15-10-505
100
10 20 3040
5060
708090100
110120
130140
150160170180
190200210220
230240
250260270280290
300310
320330340350
125015001750200022502500
Measured Azimuth Radiation Patterns – 400-450, 800-900 and 1250-2500MHz
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Tactical Vest Wearable AntennaExisting designs for 136-174MHz and 400-450MHz antenna systemsVest is adjustable by means of side tabs that velcro to back of vest
• Challenge integrating antenna into vest and retaining adjustable features
Appliqué pouch antenna overcomes this• Matching nylon loop pile fabric on exterior of
antenna pouch retains same functionality as vest• Coaxial cable contained in pouch can be laid out to
fit wearer and retained with velcro tabs
-30-25-20-15-10
-50
0
2 2 . 5
4 5
6 7 . 5
9 0
112 . 5
13 5
15 7 . 5
18 0
2 0 2 . 5
2 2 5
2 4 7 . 5
2 7 0
2 9 2 . 5
3 15
3 3 7 . 5 400425450
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Future Force Warrior BWA
Plate antenna couples to ballistic armor platesOnly over-the-shoulder wire visible on ensemble when installed
surrogate radio mounted whip
BWA over shoulder
wire
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Measured Signal StrengthFFW BWA vs Body Mounted Whip
STANDING FARM 06/08 232MHz 1WATT XTMR
-90-85-80-75-70
-65-60-55-50
100 150 200 250 300 350 400 450 500
Distance (m)
Rec
eive
d Po
wer
(dB
m) WHIP
MEGAWAVE
THEORY
PRONE FARM 06/08 232MHz 1WATT XTMR
-110
-100
-90
-80
-70
-60
-50
100 150 200 250 300 350 400 450 500
Distance (m)
Rec
eive
d Po
wer
(dB
m) WHIP
MEGAWAVE
Standing performance within 2-3dB of whipProne performance significantly better than whip
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SummaryPerformance of BWAs limited by body, equipment and nearby environmentAntennas need to operate in all body positions from standing to proneExcitation of surface/creeping waves (h < λ)Modeling vs. experiment • Fair to good agreement depending on complexity of antenna
configurationChamber/range measurements on EM phantoms required for repeatabilityDon’t forget EMC: digital to RF and RF to digital!