SDARS: Front End Antenna Design - Bradley...
Transcript of SDARS: Front End Antenna Design - Bradley...
SDARS: Front End Antenna
Design
Keven Lockwood
Advisor: Dr. Prasad Shastry
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Outline
• Project Overview
• Antenna Characteristics
• Feeding Techniques
• Performance Specifications
• Design Process
• Expected results
• Design Dependencies
• Equipment
• Schedule
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Project Overview
• Patch Antenna for receiving SDARS
– Compact size
• Idea from “A Circularly Polarized
Microstrip Antenna using Singly-Fed
Proximity Coupled Feed” by Iwasaki,
Sawada, Kawabata
– Not previously designed at BU
• Past Projects
– Greg Zomchek and Erik Zeliasz• Probe feed antenna
• Aperture coupled feed antenna
– Sasidhar Vajha• Proximity coupled, linearly polarized, 1.9
GHz patch antenna
Source: H. Iwasaki, H. Sawada, K. Kawabata. “A Circularly Polarized
Microstrip Antenna Using Singly-Fed Proximity Coupled Feed.” Institute
of Electronics, Information and Communication Engineers. September
1992. pp. 797-800.3
Circular Polarization
Above: Illustration of a right-hand circularly
polarized wave. Right: Circularly polarized waves
travelling in the +Z direction (out of page). Source
(both figures): Ulaby, Fawwaz T. Fundamentals of
Applied Electromagnetics. Pearson Education, Inc.
2007. p. 298
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System Block Diagram
AntennaLow-Noise
Amplifier
Sirius Radio
Receiver
Mixer Band pass filter IF amplifier
Local Oscillator
Active Antenna
Down Converter
Intermediate
frequency ready for
decoding
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Antenna Characteristics
• Gain
• VSWR, input
impedance
• Polarization
• 3-dB
beamwidth
• Axial Ratio
Representative plots of the normalized radiation pattern of a microwave antenna in (a) polar
form and (b) rectangular form. Source: Ulaby, Fawwaz T. Fundamentals of Applied
Electromagnetics. Pearson Education, Inc. 2007. p. 382
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Feeding Mechanism
Source: Balanis, Constantine A. Antenna Theory: Analysis and Design. 2nd ed. John Wiley & Sons, Inc. 1997. p. 725.
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Feeding Mechanism: Microstrip
• Simple to fabricate / model
• Simple to match with inset position
• Prone to spurious feed radiation, limiting
bandwidth
Source: Balanis, Constantine A. Antenna Theory:
Analysis and Design. 2nd ed. John Wiley & Sons, Inc.
1997. p. 725.
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Feeding Mechanism: Coaxial
• Easy to fabricate, difficult to model
• Narrow bandwidth
• Low spurious radiation
Source: Balanis, Constantine A.
Antenna Theory: Analysis and Design.
2nd ed. John Wiley & Sons, Inc. 1997.
p. 725.
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Feed: Aperture Coupled
• Independent
optimization of
patch and feed
• Difficult to
fabricate
• Narrow bandwidth
• Easier to model
Source: Balanis, Constantine A. Antenna Theory: Analysis and Design. 2nd ed. John Wiley & Sons, Inc. 1997. p.
725.
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Feed: Proximity Coupled
• Wide bandwidth
• Easy to model
• Low spurious radiation
Source: Balanis, Constantine A. Antenna Theory: Analysis and Design. 2nd ed. John Wiley & Sons, Inc. 1997. p.
725.
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Performance Specifications
• 2320 MHz to 2332.5 MHz (BW = 12.5
MHz)
– 100 channels, 125 kHz per channel
• VSWRmax = 2:1
• Left-hand circular polarization
• Total active gain 28.5 dB - 32.5 dB
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Antenna Design Process
Paper Design Simulation Optimization
FabricationPhysical Testing
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Paper Design
• Substrate selection– Thick, with low dielectric constant for better radiation efficiency,
larger bandwidth (top layer)
– Same dielectric constant, thin bottom layer
• Patch Dimensions– Influenced by
• Operating frequency
• Collective height and dielectric constants of the substrates
• Transmission line model equations
• Feed line dimensions– Calculated using “MSTRIP” with Zo = 50 Ohms, dielectric
constant, height of bottom substrate
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Design Dependencies
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• ɛr eff depends on h, t, and ɛr of each
• Wp and Leff are inversely proportional to fr and the ɛr eff
• Leff = L + 2*(∆L)
• ∆L is proportional to h+t
• Ws depends on h and ɛr of bottom layer
Source: Balanis, Constantine A. Antenna Theory: Analysis and Design. 2nd
ed. John Wiley & Sons, Inc. 1997. p. 729.
Simulations
• Momentum
– Uses Maxwell’s
equations
– Measures and graphs
• S11 (reflection
coefficient)
• VSWR,
• input impedance
• Radiation pattern
– Optimization through
variable sweeps
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Fabrication
• Create a template using final
simulation dimensions (out-source)
• Use template and substrate boards
to fabricate individual layers
• Carefully glue layers together
• Solder on the packaged LNA and
add SMA port (include picture of
where LNA sits / what final product
looks like
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Physical Testing
• Network analyzer
– Graphs S11,VSWR, return loss
– Gain of LNA, Noise Figure
• Anechoic chamber
– Beam pattern
– Gain
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Expected Results: VSWR
Image taken from: Erik Zeliasz, Greg Zomcheck. “SDARS Front-End Receiver: Senior Capstone Project
Report.” Bradley University Department of Electrical Engineering, May 13, 2001. p.
Simulated
VSWR of a
linearly
polarized patch
antenna.
VSWR
measures the
degree of input
impedance
match to 50
Ohms
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Expected Results: S11
• Measures return loss at a
center frequency of 1.9 GHz
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Graph taken from source: Vajha, Sashidar. “A Proximity
Coupled Active Integrated Antenna.” Bradley University, 2000.
p.26
Expected Results: Input
Impedance
21Graph taken from source: Vajha, Sashidar. “A Proximity Coupled
Active Integrated Antenna.” Bradley University, 2000. p.26
• No matching circuitry
Equipment
• Anechoic Chamber
• HP 8722C Network Analyzer
• RF fabrication machines
• CAD with Momentum
• Spectrum Analyzer
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Schedule
1/23 –
1/26
1/27 –
2/2
2/3 –
2/9
2/10 –
2/16
2/17 –
2/23
2/24 –
3/1
3/2 –
3/8
3/9 –
3/15
3/16 –
3/22
3/23 –
3/29
3/30 –
4/5
4/6 –
4/12
4/13 –
4/19
4/20 –
4/26
4/27 –
5/3
Design
Simulation/optimization
(linearly polarized
antenna)Simulation/optimization
(circularly polarized
antenna)Fabricate Antenna and
testing
Fabricate LNA board
and testing
Incorporate both the
antenna and LNA and
test
integrate with
commercial receiver
and test
Presentation and Final
Project Report
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Questions
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