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

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  1. 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 tekin@sabanciuniv.edu APS , Orlando, July 2013

  2. Outline • Motivation • Patch antenna with improved performance • Measurement setup for antenna at 77GHz • Conclusion and future work

  3. 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

  4. Integrated antenna + LNA + RF MEMS phase shifter Patch antennas 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)

  5. IHP technology for antenna and EBG structure • Metal5(patch) SiO2 11.4um Metal1(EBG structure) 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. 5

  6. Microstrip Antenna on High Dieletric Substrate(Silicon) • On-chip microstrip patch antenna (Integration of the antenna with activecircuitry) • Compact antenna sizedue to small wavelength at W band and silicon substrate • However, the substrate will cause gain and efficiency loss and also distort the radiation pattern due to surface wave. • Surface waves can easily be excited on thick and high dielectric substrates(Silicon) • pattern distortion, gain drop, cross-polarization increase Patch size: 1.1mm*1mm SW diffraction from edge GSG Probe Surface wave Silicon(ε=12, lossy) h=250um

  7. Surface wave • Propagating electromagnetic waves that occur on the interface between two dissimilar materials(Both TM & TE nature) • metal and free space • dielectric coated conductor ɛr h 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

  8. 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)

  9. Etching of the microstrip patch antenna • Localized back-side etching (LBE) is used. • Different substrate height by mechanicalpolish of Silicon • Removing silicon right under the patch reduce loss and increase gain • Maxetching size is 700umx and Min. is100um holding walls Etched regions Patch Etching size: 600*500um Silicon(ε=12, lossy) Different substrate height by polishing

  10. Uni-planar EBG structure for Supressing Surface Wave • TM10 is Patch fundamental mode (Radiating mode) • But patch supports unwanted surface waves of TM & TE nature • Electromagnetic bandgap structure(EBG) can filter SW • A type of Photonic Bandgap structure that creates bandgap • Block unwanted surface modearound antenna’s operative frequency • Increase coupling efficiency from patch mode to space mode Patch(Metal5) EBG structure (printed at Metal1)

  11. Modeling EBG structure at 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 • Only TM nature SW can cause problem(gain, cross-pol, pattern distortion) Antenna operation Freq =650um =300um Unit cell of EBG (HFSS) EBG structure

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

  13. Microstrip Antenna with improved performance(etched and surrounded by EBG) • EBG increase gain by 3dB and remove pattern distortion • Etching also decrease losses and increase gain and efficiency Pattern with EBG Pattern without EBG Distortion mainly exist in E plane After construction distortion can shift anywhere

  14. Antenna Measurement Setup at 77GHz • Setup enables reflection coefficient, gain and far-field radiation pattern measurement • E and H Plane measurement • Both co- and cross-polarization • Calibration procedure • Corrects different errors • Unwanted ambient reflection • Absorbing material • Time domain filtering

  15. 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

  16. W-Band Antenna Measurement Setup Network Analyzer50 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) Rotating Arm Standard Horn

  17. Antenna S-parameter measurement at 77GHz • S parameter of a dipole antenna measured by our setup • S parameter of a sample dipole antenna from previous work is measured • 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

  18. Conclusion and future work • Patch antenna with EBG structure is introduced. • S-parameter and radiation pattern will be measured for the EBG patch antenna • EBG structure can be used to reduce mutual coupling between array elements. 18