integrated dual band gsm antenna design
TRANSCRIPT
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Integrated Dual-Band GSM Antenna
design Marli Strydom CST AG
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Problem description / specification
Embedded antenna design using Antenna Magus
Fullwave 3D simulation using CST STUDIO SUITE
Antenna matching using Optenni Lab
Conclusion
Outline
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Problem Description
Theft and predator
alert device
Task: Replace an off-the-shelf dual
band GSM antenna with a cheaper,
printed, integrated antenna.
All images courtesy of Etse Electronics (www.etse.co.za) off-the-shelf antenna obscured
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Possible Advantages
Planar nature allows antenna to be printed on PCB
reduction in manufacturing costs
reduction in assembly costs
Higher antenna efficiency
Longer amplifier & battery life
Possible Disadvantages
Engineering time and effort
Software cost?
Integrated Antenna Design
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Dual band GSM 890 MHz – 960 MHz
1710 MHz – 1879.8 MHz
Antenna Specifications
Substrate - 4-layer FR4
Maximum available distance between two
metal layers is 1.203 mm
Max. antenna dimension: 70 mm x 10.5 mm
70 mm
10.5mm antenna
off-the-shelf antenna model obscured
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Initial Integrated Antenna Design
using Antenna Magus
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Finding the Right Antenna
2 templates matched 3/3 keywords – select the IFA
Printed inverted-F antenna (IFA)
Known antennas(>500)
Antennas in Magus (>200)
“GSM” (55)
“Planar” (44)
“Printed” (2)
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Design Printed IFA
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Estimated Performance (Single Elements)
Export Model
to CST MWS...
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Simulated Results: Combined Elements
Simulation results on simplified
dielectric board
Retune antenna by quick
parameter sweep
900 MHz
element
1800 MHz
element
element length: l
detuned performance: l = 2.3 mm retuned performance: l = 3 mm
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Model and Simulate
New Antenna in CST MWS
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The following changes have to be made:
Reduce the substrate/ground plane size
Add components and tracks
Adjust Antenna Size
18 mm 10.5 mm
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Effect of Fitting Antenna on Reduced Substrate
10.5 mm /0.41 inches
Real impedance has
changed from 44 to 8 Ohm
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Antenna Magus Guidelines: Change Design
Shorting stub to compensate for
capacitance
Reduced height = decreased
input impedance
Design Guidelines
Info Browser
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Antenna fits inside design area and
real impedance at 1800 is increased
from 8 to 30 Ω.
Match Impedance by
Adding an Extra Shorting Stub
Add stub to
compensate for
added capacitance
1800 band
element
moved
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Import PCB into CST MWS
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Simulation now includes: Reduced 900 MHz and
1800 MHz elements
Tracking device PCB
Battery
Housing
Simulation Including PCB, Battery
Discrete port (via onto RF chip)
Lengthen elements
Simulation time < 30 min
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Design well matched at centre of both bands
Small substrate size results in reduced impedance
bandwidth
Required: good match
across GSM bands!
Simulation Results
GSM 900 and 1800 bands
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Matching Network Design
using Optenni Lab
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Fast and easy-to-use matching circuit optimization
tool for antenna designers
Main features:
Fast automatic matching circuit generation
Estimation of bandwidth potential
Two-way link to CST STUDIO SUITE
Mupti-port matching
Matching Network using Optenni Lab
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Target: GSM 900 and
GSM 1800 bands
Original minimum
efficiency (red bars):
-4.2 dB in 900 band
-10.4 dB in 1800 band
Antenna Without Matching
Blue curve: S11
Green curve: efficiency
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Bandwidth potential for a
lossless two-component
matching circuit at 6dB
return loss level
GSM 900: 33 MHz
(wanted: 70 MHz)
GSM 1800: 46 MHz
(wanted: 170 MHz)
Thus: antenna is difficult
to match!
Bandwidth Potential
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Minimum efficiency
about -3.6 dB (45%)
Performance drops by
0.5 dB when losses are
considered
Dual Band Matching Circuit
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Antenna in Realistic Environment
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Impedance match
unchanged
Farfield changes
Device in More Realistic Environment 900 MHz
1.8 GHz
tracker positioned 9 cm from sheep
simulation took about 1.5 hours
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Friis Range Comparison
GSM bands
Integrated antenna
With matching
Frequency [GHz]
Range [
km
]
Friis parameters:
Pt = 2 W; Pr = -80 dBm
S11,r = -40 dB
Gr = 9 dBi
900 MHz: Gt between 0 and 2.8 dBi
1800 MHz: Gt between 0 and 4.5 dBi
best case:
30 km
worst case:
22 km best case: 18km
worst case: 11 km
Matching improvement
2
,11
2
,11
2
114
rtrt
t
r SSR
GGP
P
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A new customised integrated antenna was designed for
this particular tracking device to operate in the GSM
900 band and GSM 1800 bands.
The design process was made easier by using advanced
tools like Antenna Magus, CST MICROWAVE STUDIO, and
Optenni Lab.
The printed design can reduce unit cost per tracking
device by replacing an off-the-shelf antenna and
reducing the labour required to assemble the antenna,
and can have better performance.
Conclusion