Mohammad Hossein Nemati, Ibrahim Tekin

** Electronics Engineering, Sabancı University, 34956 Istanbul, Turkey tekin@sabanciuniv.edu

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A 77GHz on-chip Microstrip patch antenna with suppressed surface wave using EBG substrate

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

Two microstrip patch antenna Two LNA with 15 dB gainTwo RF MEMS 4 bit phase shifterLess than 10 mm2 chip area (2.6 mm X 3.9 mm)

Patch antennas

IHP technology for antenna and EBG structure

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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.

Grounded board for RF measurement

Silicon substrate20ohm-cm Etched part

SiO2Metal1(EBG structure)

Metal5(patch)

250um

11.4um

Microstrip Antenna on High Dieletric Substrate(Silicon)

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 substrateo 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

Silicon(ε=12, lossy)

Patch size: 1.1mm*1mm

h=250um

GSG ProbeSurface waveSW diffr

action fro

m edge

Surface wave

o Propagating electromagnetic waves that occur on the interface between two dissimilar materials(Both TM & TE nature)

o metal and free space

o dielectric coated conductor

7TM Surface wave mode has same polarization with patch mode

ɛrh

a) Dielectric Coated Substrate b) TM0 mode pattern for coated substrate C) Patch Antenna Mode(E field)

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

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

Silicon(ε=12, lossy)

Etched regions

Different substrate heightby polishing

Patch

holding walls

Etching size: 600*500um

Uni-planar EBG structure for Supressing Surface Wave

o TM10 is Patch fundamental mode (Radiating mode)

• But patch supports unwanted surface waves of TM & TE natureo 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

EBG structure(printed at Metal1)

Patch(Metal5)

Modeling EBG structure at HFSS

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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 Only TM nature SW can cause problem(gain, cross-pol, pattern distortion)

=650um

=300um

Unit cell of EBG (HFSS)EBG structure

Antenna operation Freq

Microstrip Antenna with improved performance(etched and surrounded by EBG)

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Presence of the EBG drops the resonance frequency which can be removed easily by tuning the length of the patch.

a) Patch antenna surrounded by EBG b) Return Loss vs. Frequency

Microstrip Antenna with improved performance(etched and surrounded by EBG)

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o EBG increase gain by 3dB and remove pattern distortiono Etching also decrease losses and increase gain and efficiency

Pattern with EBGPattern without EBGDistortion mainly exist in E plane

After construction distortion can shift anywhere

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

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Network Analyzer

50 GHz – PNA 5245A

Table for Extender, cascade probe , probe positioner and AUT

Horn antenna and bent WG

Extender

W-Band Antenna Measurement Setup

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Network Analyzer 50 GHz – PNA 5245A

AUT & GSG probeTwo type of GSG probe are available with 90 degree spatial difference(to switch from E-plane to H-plane)

Extender

Rotating Arm

Standard Horn

Antenna S-parameter measurement at 77GHz

o S parameter of a dipole antenna measured by our setup

o S parameter of a sample dipole antenna from previous work is measuredo Due to delay in delivery of patch antenna we were not able to measure the

result for patch

Freq(GHz)a) Dipole antenna measured by our setup

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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.