Transcript An Indoor Positioning System Based on Global Positioning

A 77GHz on-chip Microstrip patch antenna with
suppressed surface wave using EBG substrate
Mohammad Hossein Nemati, Ibrahim Tekin
** Electronics Engineering, Sabancı University, 34956 Istanbul, Turkey
[email protected]
APS , Orlando, July 2013
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Outline
 Motivation
 Patch antenna with improved performance
 Measurement setup for antenna at 77GHz
 Conclusion and future work
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Motivation
 Millimeter wave systems are promising
 high speed comunication
 less interference
 Single chip solution including the antenna (antenna size is comparable to
the chip size and integration of chip with antenna is feasible)
 We encounter more civilian use of millimeter wave radars especially in

navigation
 road traffic control
 safety for highway driving (short range automotive radar at 77 GHZ band)
 Measurement at millimeter wave frequency is challenging. Minimizing the
measurement uncertainty is critical in the development of new mm-wave
applications.
 High precision devices
 High skills needed for measurement and calibration of devices
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Integrated antenna + LNA + RF MEMS phase shifter
Patch
antennas
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Two microstrip patch antenna
Two LNA with 15 dB gain
Two RF MEMS 4 bit phase shifter
Less than 10 mm2 chip area (2.6 mm X 3.9 mm)
IHP technology for antenna and EBG structure
SiO2
Metal1(EBG structure)

Metal5(patch)
11.4um
250um
Silicon substrate
20ohm-cm
Etched part
Grounded board for RF measurement
 5 metal layers for antenna and EBG structure
 Metal5 layer is used for Antenna and Metal1 line is used for
implementing EBG structure.
 Localized back-side etching (LBE) module to etch the lossy substrate
under the antenna to increase the gain.
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Microstrip Antenna on High Dieletric Substrate(Silicon)
Patch size: 1.1mm*1mm
GSG Probe
Surface wave
Silicon(ε=12, lossy)
o On-chip microstrip patch antenna (Integration of the antenna with active circuitry)
o Compact antenna size due to small wavelength at W band and silicon substrate
o However, the substrate will cause gain and efficiency loss and also distort the radiation
pattern due to surface wave.
o Surface waves can easily be excited on thick and high dielectric substrates(Silicon)
•
pattern distortion, gain drop, cross-polarization increase
h=250um
Surface wave
o Propagating electromagnetic waves that occur on the interface between two
dissimilar materials(Both TM & TE nature)
h
o
metal and free space
o
dielectric coated conductor
ɛr
a) Dielectric Coated Substrate
b) TM0 mode pattern for coated substrate
C) Patch Antenna Mode(E field)
TM Surface wave mode has same polarization with patch mode
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Solutions to improve gain and radiation pattern
•
Substrate can be etched
• Etching establish a low effective dielectric-constant environment
• Less localized EM fields
• Increase the antenna gain and efficiency
•
EBG structures can be patterned close to the antenna to
stop the SW propagation.
• EBGs are sub-class of Meta-Material
• Creates band-gap for surface wave
• Different type of EBG structure are available
• Uni-planar Electromagnetic Band-Gap is chosen due to construction
simplicity(no need for via)
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Etching of the microstrip patch antenna
holding walls
Etched regions
Patch
Etching size: 600*500um
Silicon(ε=12, lossy)
Different substrate height
by polishing
o Localized back-side etching (LBE) is used.
• Different substrate height by mechanical polish of Silicon
• Removing silicon right under the patch reduce loss and
increase gain
• Max etching size is 700umx and Min. is100um
Uni-planar EBG structure for Supressing
Surface Wave
Patch(Metal5)
EBG structure
(printed at Metal1)
o TM10 is Patch fundamental mode (Radiating mode)
•
But patch supports unwanted surface waves of TM & TE nature
o Electromagnetic bandgap structure(EBG) can filter SW
•
A type of Photonic Bandgap structure that creates bandgap
•
Block unwanted surface mode around antenna’s operative frequency
•
Increase coupling efficiency from patch mode to space mode
Modeling EBG structure at HFSS
Antenna operation Freq
=650um
=300um
EBG structure
Unit cell of EBG
(HFSS)
 Unit cell of EBG modeled at HFSS to derive it’s propagation constant
 Dispersion diagram for EBG structure
Propagation at first Brillouin zone
propagation constant of surface wave at different frequency and
directions
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 Only TM nature SW can cause problem(gain, cross-pol, pattern distortion)
Microstrip Antenna with improved
performance(etched and surrounded by EBG)
a) Patch antenna surrounded by EBG

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b) Return Loss vs. Frequency
Presence of the EBG drops the resonance frequency which can be removed easily by
tuning the length of the patch.
Microstrip Antenna with improved
performance(etched and surrounded by EBG)
o EBG increase gain by 3dB and remove pattern distortion
o Etching also decrease losses and increase gain and efficiency
Distortion mainly exist in E plane
After construction distortion can shift anywhere
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Pattern with EBG
Pattern without EBG
Antenna Measurement Setup at 77GHz
o Setup enables reflection coefficient, gain and far-field radiation pattern
measurement
•
E and H Plane measurement
• Both co- and cross-polarization
o Calibration procedure
• Corrects different errors
o Unwanted ambient reflection
• Absorbing material
• Time domain filtering
Indoor Antenna measurement setup
Extender
Network Analyzer
50 GHz – PNA 5245A
Horn antenna
and bent WG
Table for Extender,
cascade probe , probe
positioner and AUT
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W-Band Antenna Measurement Setup
Network Analyzer 50 GHz – PNA 5245A
Extender
AUT & GSG probe
Two type of GSG probe
are available with
90 degree spatial
difference(to switch
from E-plane to H-plane)
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Rotating Arm
Standard Horn
Antenna S-parameter measurement at 77GHz
o S parameter of a dipole antenna measured by our setup
Freq(GHz)
a) Dipole antenna measured by our setup
o S parameter of a sample dipole antenna from previous work is measured
o Due to delay in delivery of patch antenna we were not able to measure the
result for patch
Conclusion and future work
o Patch antenna with EBG structure is introduced.
o S-parameter and radiation pattern will be
measured for the EBG patch antenna
o EBG structure can be used to reduce mutual
coupling between array elements.
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