Applied Research Laboratory Technical Report A Switchable Magnetic Low-Index Metamaterial for Use in a Dynamically Reconfigurable Beam- Scanning Lens Antenna With a Single Feed by Jeremiah P. Turpin, Dr. Douglas H. Werner and Dr. Douglas E. Wolfe Approved for public release, distribution unlimited. PENN STATE 8 5 5 The Pennsylvania State University The Applied Research Laboratory P.O. Box 30 State College, PA 16804 A Switchable Magnetic Low-Index Metamaterial for Use in a Dynamically Reconfigurable Beam-Scanning Lens Antenna With a Single Feed By Jeremiah P. Turpin and Dr. Douglas E. 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Z39.18 Adobe Professional 7.0 The Pennsylvania State University The Graduate School A SWITCHABLE MAGNETIC LOW-INDEX METAMATERIAL FOR USE IN A DYNAMICALLY RECONFIGURABLE BEAM-SCANNING LENS ANTENNA WITH A SINGLE FEED A Dissertation in Electrical Engineering by Jeremiah Paul Turpin © 2014 Jeremiah Paul Turpin Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy December 2014 Approved for public release; distribution unlimited The dissertation of Jeremiah Paul Turpin was reviewed and approved* by the following: Douglas H. Werner Professor of Electrical Engineering Dissertation Advisor Pingjuan Werner Professor of Electrical Engineering Victor Pasko Professor of Electrical Engineering Douglas Wolfe Associate Professor of Material Science and Engineering Kultegin Aydin Professor of Electrical Engineering Department Chair 'Signatures are on file in the Graduate School. Abstract Metamaterials and Transformation Optics (TO) have been used to design and implement many novel electromagnetic devices that can achieve effects not possible using conventional materials. Compact high-gain antennas are one of the more popular and successful emerging applications for the new TO and metamaterial design approaches. This dissertation details an extension of uniaxial near-zero- index metamaterial lenses through the incorporation of a tunable or reconfigurable metamaterial as a replacement for the static metamaterial of the original antenna. A design is presented for a beam-scanning TO lens that allows an arbitrary number of beams at controlled magnitudes to be dynamically synthesized from a single omnidirectional source, unlike the equivalent antenna constructed using an array. A cylindrical slab of zero-index magnetic metamaterial controls the ra- diation pattern by altering the effective shape of the lens through switching of selected regions 'off' to emulate free-space conditions. A design for a switchable metamaterial is presented that allows for digital control over its bulk properties, from near-zero-index to near-free-space at the targeted operational frequency. Ex- tensive modeling and simulations were performed for the design of the lens and metamaterial and during the analysis of measurement results. Initial prototypes of the tunable metamaterial were fabricated and characterized to confirm the original measurements, and the design updated to incorporate the measured data. These measurements were performed using custom test fixtures manufactured specifi- cally for this project. Finally, a simplified prototype lens was manufactured and characterized in an anechoic as a proof-of-concept for the design. This dissertation presents the lens and metamaterial specifications, as well as the design process and considerations that were determined for practical tunable and reconfigurable metamaterials. Although the focus is on the particular example of the beam-scanning reconfigurable antenna, the analysis and modeling methods presented here are applicable to any reconfigurable metamaterial application. in Table of Contents List of Figures vii Acknowledgments xv Dedication xvii Chapter 1 Introduction and Previous Work 1 1.1 Reconfigurable Antennas and Limitations 5 1.2 Metamaterials 6 1.3 Transformation Optics 10 1.4 Metamaterial and Transformation Optics-based Antennas 12 1.5 Original Contributions of This Work 16 Chapter 2 Reconfigurable Metamaterial Lens Antenna 17 2.1 qTO-derived near-ZIM lens 19 2.2 Cylindrical magnetic lens 21 2.2.1 Material Parameters 22 2.2.2 Design Process 23 2.2.3 Excitation Considerations 25 2.2.4 Metamaterial Selection 25 2.2.5 Control Signal Distribution Topology 27 2.3 Possible Feed Antennas 31 2.4 Vertical scanning 34 2.5 Upper Hemispherical Beam Scanning 36 2.6 Summary of Selected Prototype Lens Design Approach 39 IV Chapter 3 Metamaterial Design and Measurements 42 3.1 Reconfigurable Metamaterial Design Considerations 43 3.1.1 Viable Tuning Mechanisms 44 3.1.2 Control Circuits 45 3.1.3 Metamaterial Resonators and Unit Cell 49 3.1.4 Unit Cell Interconnection 50 3.1.5 PCB Design and Layout Software 51 3.1.6 Bias Supply Regulation and Board-Level Considerations . . 54 3.2 Initial Metamaterial Design and Prototype 54 3.2.1 Control Signals 55 3.2.2 Control and Bias Circuitry 58 3.2.3 PCB Layouts and Simulations 59 3.2.4 Prototype Fabrication and Assembly 61 3.3 Initial Metamaterial Prototype Characterization 64 3.3.1 Waveguide test fixture design and construction 66 3.3.2 Monopole test fixture design and construction 72 3.3.3 Microstrip bias tee design and construction 73 3.3.4 Microstrip test fixture design and construction 74 3.3.5 Measurement and Simulation Deembedding and Calibration 79 3.3.5.1 TRL Calibration Algorithm 79 3.3.6 Varactor Characterization 86 3.3.7 Modeling refinements 86 3.3.7.1 Increase simulation resolution 89 3.3.7.2 Trace material 89 3.3.7.3 Dielectric boundary 89 3.3.7.4 Soldermask 89 3.3.7.5 Hex cell orientation 90 3.3.7.6 Single-varaetor measurements 90 3.3.7.7 Summary of changes 91 3.3.8 Waveguide measurements 92 3.3.9 Monopole measurements 92 3.4 Design revisions 98 3.4.1 Voltage Regulator and Level Shifter 102 Chapter 4 Lens Prototype 106 4.1 Feed antenna 107 4.1.1 Substrate-integrated waveguide slot antenna 108 4.1.1.1 Microstrip Transition 109 4.1.1.2 Slot Dimensions and Placement . . . '. 109 4.1.1.3 Final Tuning and Results 110 4.1.2 Substrate-integrated Cavity-backed Slot Antenna Ill 4.1.3 Stripline-integrated Slot Antenna Ill 4.2 Static Metamaterial Lens 113 4.3 Prototype Layout 116 4.4 Prototype Construction 117 4.4.1 Controller 122 Chapter 5 Conclusions and Future Work 132 5.1 Lessons from the Lens Prototype and Future Revisions 133 References 138 Publications 145 VI List of Figures 1.1 (a) The electromagnetic interactions of a real material can be ex- pressed in terms of a relative e and \i . (b) The structures that r r compose a metamaterial, although larger than the molecular and atomic-scale effects of a real material, can, in many circumstances, be used to compute an averaged electromagnetic response and the assignment of an effective e and // 8 r r 1.2 Various metamaterial unit cell designs from the literature 9 1.3 Illustration of three categories of Uniaxial ZIM lens antennas. In these antennas, either the permeability or the permittivity, but not both, are near zero and are uniaxial with the optical axes aligned as indicated by the arrows drawn within each region, (a) Parallel (in-plane) optical axis to direction of propagation and planar beam- forming with a vertical feed; radiation pattern controlled by optical axis, (b) Perpendicular (out-of-plane) optical axis to direction of propagation and planar beamforming with a vertical feed; radiation pattern controlled by shape of ZIM slab, (c) Parallel (out-of-plane) optical axis to direction of propagation and vertical beamforming with a horizontal feed and ground plane; radiation pattern con- trolled by optical axis and feed properties 13 2.1 (a) The parallel ZIM collimation mode requires the direction of the optical axis to be changed (c) in order to change the direction of beam propagation, requiring two dimensions of control over the index, (b) The perpendicular ZIM mode requires only an on-off. one-dimensional control over the index (d) to change the shape or boundary contour of the lens in order to change the radiation pattern. 18 2.2 Changing the lens dimensions changes the radiation pattern 19 2.3 A beam is radiated from each face of the structure. Sufficiently large lenses can successfully resolve beams at small angular increments. . 19 2.4 Early simulation of a wire-mesh dipole array near-zero index meta- material lens 20 Vll