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A Critical Look at the Performance Enhancement of Small Antennas using Metamaterials

A Critical Look at the Performance Enhancement of Small Antennas using Metamaterials. Raj Mittra Electromagnetic Communication Laboratory Penn State University E-mail: rajmittra@ieee.org. META 101 ALL YOU WANTED TO KNOW ABOUT METAMATERIALS…… WHAT’S NEW ABOUT METAMATERIALS

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A Critical Look at the Performance Enhancement of Small Antennas using Metamaterials

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  1. A Critical Look at the Performance Enhancement of Small Antennas using Metamaterials Raj Mittra Electromagnetic Communication Laboratory Penn State University E-mail: rajmittra@ieee.org

  2. META 101 ALL YOU WANTED TO KNOW ABOUT METAMATERIALS…… WHAT’S NEW ABOUT METAMATERIALS METAMATERIALS—THE HOLY GRAIL! YOU HAVE ANSWERS, WE HAVE QUESTIONS TITLES, TITLES

  3. CLASSIFICATON OF METAMATERILS DPS ENG DPS Regular Dielectrics MNZ MNZ DNG MNG ENZ ENZ Loughborough Antennas and Propagation Conference – 2006 F. Bilotti – Potential Applications of Matamaterials in Antennas

  4. Taxonomy of Metamaterials • Double Negative (DNG) materials (Periodicity d << λ) • Elements and distances between them are much smaller than a wavelength (Effective medium concepts, simultaneous effective negative permittivity and permeability) • Have several names including left-handed materials, backward-wave materials, Negative Index of Refraction (NIR) materials, etc. • Electromagnetic Band Gap (EBG) materials (Periodicity d ~ λ) • Element Distances are on the order of half a wavelength or more (Periodic medium concepts) • Photonic crystals, Photonic Band Gap materials (PBG), Artificial Magnetic Conductors (AMC), High Impedance Surfaces (HIS)

  5. Q. SO WHAT EXOTIC THINGS WOUD YOU DO WITH METAMATERIALS, IF YOU HAD THEM? QUESTION, QUESTION

  6. 1990 2000 Handset evolution Size Weight Price Functionality Design • Antennas: • Size reduction: effect on polarisation, bandwidth, efficiency and manufacturing tolerances • Reduced ground plane: effect on matching, bandwidth, patterns and user interaction • Price reduction: low cost elements

  7. Antennas for mobile terminals Internal mobile phone antennas Antennas for PCMCIA cards Customised antennas for specific applications

  8. Applications • Mobile phones • GSM modules for customised applications • PCMCIA • Special terminals • Emergency phones • Code bars readers • Credit cards terminals…

  9. Effect of the components • Limited available volume • Circuits and components • Antenna: only component with physical limitations for miniaturisation!

  10. iPoDs and Implants Future of body centriccommunications

  11. * Technology for automatic identification of objects * Application : logistics,security system,animal tracking transportation and manufcacturing process control RFID (Radio Frequency Identification ) System

  12. They require combining expertise in the fields of electrical engineering and materials science. Artificial Dielectrics and their Applications: Explore metamaterials and Investigate their viability in enhancing antenna performance. Antennas and Metamaterials: Size Reduction Other Improvements, e.g., bandwidth, directivity and pattern shape. *Fine print—That’s the promise anyway!! Why are Metamaterials interesting?

  13. LET’S BEGIN WITH A LITTLE HISTORY HOW DID WE GET STARTED ON THE DNG STUFF? WHAT WOULD THEY DO FOR US ONCE WE HAVE THEM? Engineered media that have a negative index of refraction ( negative permittivity and Permeability) V.G.Veselago, SOV. Phys, 10, 509 1968 The ‘Perfect Lens’ Perfect reconstruction, High Transverse Wave vectors Imaginary Longitudinal component Evanescent Fields

  14. Realization of Metamaterials V.G.Veselago, SOV. Phys, 10, 509,1968 • Metamaterials are artificial materials that exhibit electromagnetic responses generally not found in nature. • Engineered media that have a negative index of refraction ( negative permittivity and permeability ) • Predicted in 1968 by V.G.Veselago • E,H and K form a left-handed system of vectors Composite Metamaterial (CMM) D.R.Smith and S.Schultz, UCSD

  15. Realization (contd.) • Realization of Conventional Metamaterial • Negative ε • Thin metallic wires are arranged periodically • Effective permittivity takes negative values below plasma frequency • Negative μ • An array of split-ring resonators (SRRs) are arranged periodically ( Koray Aydin, Bilkent University, Turkey Sep 6 , 2004 )

  16. Effective Parameters Inversion Method • Can be applied to both simple and complicated structures • Can use both numerical and experimental data • S-parameters for metamaterials are more complex • Ambiguities in the inversion formulas

  17. Effective Parameters A continuous material can be characterized by the complex variables S11 and S21, or n and z where and Inversion yields, and Where and the signs in the above equation are chosen using the conditions and

  18. Effective Parameters • The propagation constant is then obtained from the equation , • Once the impedance and the propagation constant are obtained the effective parameters can be calculated.

  19. Extraction of constitutive effective parameters from S-parameters for normalincidence

  20. <= 1 2 Equations used in the inversion approach ( 2 different roots ) • Compute Z: • Compute n: • Compute effective  and : - ( 2 different roots ) Y = (branches with different m) Conditions used: Z’ > 0 and n”<=0, ”<= 0 and ” <= 0 Iterative approach to pick n such that n is continuous and

  21. Example 1: 2-D infinite array of dipoles for normal incidence Z Unit cell BC used X and Y: PBC Z: PML Plane of transmission Ei, Et and Er are the contributions from the zeroth Floquet mode measured on the corresponding planes. Plane of reflection Plane wave source EY X Y

  22. Solutions for all branches ( m=0, -1 and +1) and 2 roots Determine the solution by using ref. (1): • By enforcing ” <0 and ” <0, only m=0 can be solution. • By enforcing n”<0, the correct root can be determined. (2) (1) (1)

  23. Extracted parameters: 2-D infinite array of dipoles

  24. Example 2: 2-D infinite array of split-rings for normal incidence Z Unit cell BC used X and Y: PBC Z: PML Plane of transmission Plane of reflection Plane wave source EY X Y

  25. Extracted parameters: 2-D infinite array of split-rings Note: The shaded area represents the non-physical region, where ” or ” > 0. In this region, we choose the branch that best connect n just before and after this band.

  26. Example 3: 2-D infinite array of split-rings + dipoles for normal incidence Z Unit cell BC used X and Y: PBC Z: PML Plane of transmission Plane of reflection Plane wave source EY X Y

  27. Extracted parameters: 2-D infinite array of split-rings+dipoles (1-layer) Note: The shaded area represents the non-physical region, where ” or ” > 0.

  28. 2-D Infinite array of split-rings + dipoles ( 2-layer ) Note: The shaded area represents the non-physical region, where ” or ” > 0.

  29. Extracted parameters: 2-D infinite array of split-rings+dipoles (2-layer) Note: The shaded area represents the non-physical region, where ” or ” > 0.

  30. 2-D Infinite array of split-rings + dipoles ( 3-layer ) Note: The shaded area represents the non-physical region, where ” or ” > 0.

  31. Extracted parameters: 2-D infinite array of split-rings+dipoles (3-layer) Note: The shaded area represents the non-physical region, where ” or ” > 0.

  32. 2-D Infinite array of split-rings + dipoles ( 4-layer ) Note: The shaded area represents the non-physical region, where ” or ” > 0.

  33. Extracted parameters: 2-D infinite array of split-rings+dipoles (4-layer) Note: The shaded area represents the non-physical region, where ” or ” > 0.

  34. Comparison of effective parameters for 1 to 4-layer split-ring + dipole Note: The effective parameters for 1-4 layers are almost the same, except that more resonant peaks can be seen for more layers.

  35. Refraction in DNG Prisms DNG DPS

  36. PROPOSED APPLICATIONS OF METAMATERIALS Ziolkowski’s group: resonant sub-ldipole antennas ENG DPS Roma Tre group: resonant sub-lpatch and leaky wave antennas Loughborough Antennas and Propagation Conference – 2006 F. Bilotti – Potential Applications of Matamaterials in Antennas

  37. SRR Design Ring Dimensions Side length – 3mm Thickness - 0.25mm Gap - 0.5mm Waveguide Dimensions X-band waveguide Width – 19.25mm Height – 10.625mm Terminated by PML walls to avoid reflections Ring Field Planes z x y Voltage Measurement points The SRR was placed vertically with the gap-bearing side parallel to the direction of propagation.

  38. S-parameters and Effective Parameters: Parallel Orientation • Comparison of real parts of effective permittivity and effective permeability • Comparison of reflection and transmission coefficients obtained from measurements and simulations (Dimensions Scaled)

  39. Field Distributions Confirm the Resonant Permeability Behavior Before the resonance Amplitude Phase Amplitude After the resonance Phase

  40. SRR Design : Perpendicular Orientation Ring Dimensions Side length – 3mm Thickness - 0.25mm Gap - 0.5mm Waveguide Dimensions X-band waveguide Width – 19.25mm Height – 10.625mm Terminated by PML walls to avoid reflections Ring Field Planes z x y Voltage Measurement points The SRR was placed vertically with the gap-bearing side perpendicular to the direction of propagation.

  41. Perpendicular Orientation - Results Comparison of real parts of effective permittivity and effective permeability Comparison of reflection and transmission coefficients obtained from measurements and simulations (Dimensions scaled)

  42. Composite Unit Cell - Results • Comparison of real parts of effective permittivity and effective permeability • Comparison of reflection coefficients obtained from simulations for the three cases

  43. Verification Confirmation of Backward Wave Propagation Distance d of the points from the source d Source z Phase of the field measured at three different points along the waveguide inside the DNG unit cell y Increase in phase ( phase advance) for points away from the source in the frequency range where the effective parameters are simultaneously negative.

  44. Simulation and Field Analysis x x y y z y BC-SRRS Waveguide Coaxial feed Ez in XY-plane Pass Band below cutoff 8.6 GHz 8.4 GHz Hz in YZ-plane • SRRs are coupledas seen from the magnitude and phase distributions of the E and H fields • The axial magnetic moment does not exist and so cannot cause negative permeability. • Wave tunneling might be due to a resonance wave propagation along the SRR chain 37600 62000 8.8 GHz 8.7 GHz 74000 76300 9.1 GHz 8.9 GHz 8.7Ghz 68700 79400

  45. K – Band Wave Guide Pass Band below Cutoff Waveguide Dimensions Width – 10.66mm Height – 4.2mm Cut off – 14.07GHz Ring Dimensions Side length – 1.7mm Thickness - 0.25mm Gap - 0.48mm Magnitude and Phase of Ex near the SRR Magnitude Phase Cut Off z y Regular Half-wavelength Resonance of the SRR ( Negative Permeability) Transmission Coefficient

  46. Field Distributions • Components of E and • H fields normal to the • SRR plane Ex (13.65GHz) Ex(13.95GHz) • Magnitude of the fields • is more than 3 times • higher than that at other • frequencies 9.97e+005 4.89e+005 • Separation ~ 0.35Ghz • and the fact that the • Half-wavelength • resonance occurs at two • frequencies indicates that • a slow wave mode • propagates through the • SRR waveguide below • cutoff z y 3.07e+002 1.03e+003 Hx(13.95Ghz) Hx(13.65GHz) Half wavelength Resonance Full wavelength Resonance

  47. Physical phenomena related to metamaterial complementary pairs 3/3 Ziolkowski’s group: resonant sub-ldipole antennas ENG DPS Roma Tre group: resonant sub-lpatch and leaky wave antennas Loughborough Antennas and Propagation Conference – 2006 F. Bilotti – Potential Applications of Matamaterials in Antennas

  48. THE PERFECT LENS? TIME TO RAISE A FEW ??

  49. Refraction in DNG Prisms DNG DPS

  50. Equivalent Medium Approach It is a Common practice to replace an artificial dielectric with its equivalent ε and μ perform an analysis of composite structures (antenna + medium) using the equivalent medium. But this can lead to significant errors and wrong conclusions R T Exit angle? . . . . . . . . . . . . Single layer Multiple layers Floquet harmonics

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