Mohammad Hossein Nemati, Ibrahim Tekin ** Electronics Engineering, Sabancı University, Istanbul, Turkey 1 A 77GHz on-chip Microstrip patch antenna with suppressed surface wave using EBG substrate 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 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) Patch antennas

IHP technology for antenna and EBG structure 5 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 substrate 20ohm-cm Etched part SiO2 Metal1(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 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 Silicon(ε=12, lossy) Patch size: 1.1mm*1mm h=250um GSG Probe Surface wave SW diffraction from 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 7 TM Surface wave mode has same polarization with patch mode ɛrɛr h a) Dielectric Coated Substrateb) TM0 mode pattern for coated substrateC) 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) 8

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 height by polishing Patch holding walls Etching size: 600*500um

Uni-planar EBG structure for Supressing Surface Wave o TM 10 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 EBG structure (printed at Metal1) Patch(Metal5)

Modeling EBG structure at HFSS 11 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) 12 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) 13 o EBG increase gain by 3dB and remove pattern distortion o 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

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 15 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 16 Network Analyzer 50 GHz – PNA 5245A AUT & GSG probe Two 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 measured o 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 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.