PhD Thesis Dissertation Multifunctional Metamaterial Designs for Antenna Applications PhD Thesis Author Pere Josep Ferrer Gonz´alez AntennaLab - TSC Universitat Polit`ecnica de Catalunya E-mail: [email protected] PhD Thesis Advisors Jos´eMar´ıa Gonz´alez Arbes´u and Jordi Romeu Robert AntennaLab - TSC Universitat Polit`ecnica de Catalunya E-mail: [jmgonzalez, romeu]@tsc.upc.edu Thesis submitted for the degree of Doctor of Phylosophy from the Universitat Polit`ecnica de Catalunya Barcelona, June 2015 Multifunctional Metamaterial Designs for Antenna Applications Pere Josep Ferrer Gonz´alez Ph.D. program on Signal Theory and Communications (TSC). Universitat Polit`ecnica de Catalunya (UPC). Barcelona (Spain) This work has been partially supported by the Spanish Comisi´on Interministerial de Ciencia y Tecnolog´ıa (CICYT) of the Ministerio de Educaci´on y Ciencia (MEyC) and FEDER funds through the grants TEC2006-13248-C04-02/TCM, TEC2007-66698- C04-01/TCM, TEC2007-65690, TEC2008-06764-C02-01, TEC2009-13897-C03-01/TEC, and CONSOLIDER CSD2008-00068, by the Ram´on y Cajal Programme and by the European Commission through the METAMORPHOSE NoE project FP6/NMP3-CT- 2004-500252. Copyright c 2015 by Pere Josep Ferrer Gonz´alez, AntennaLab, TSC, UPC, Barcelona, Spain. All rights reserved. Reproduction by any means or translation of any part of this work is forbidden without permission of the copyright holder. Als meus pares Francisco i Francisca. Abstract Over the last decades, Metamaterials (MTMs) have caught the attention of the sci- entific community. Metamaterials are basically artificially engineered materials which can provide unusual electromagnetic properties not present in nature. Among other novel and special EM applications, such as the negative refraction index (NRI) appli- cation, Metamaterials allow the realisation of perfect magnetic conductors (PMCs), which are of interest in the development of smaller and more compact antenna systems composed of one or more antennas. In this context, this thesis is focused on investigating the feasibility of using meta- material structures to improve the performance of antennas operating at the microwave frequencies. The metamaterial design process is challenging because metamaterials are primarily composed of resonant particles, and hence, their response is frequency de- pendent due to the dispersive behaviour of their effective medium properties. However, one can take advantage of this situation by exploiting those strange properties while finding other antenna applications for such metamaterial designs. For the case of the PMC applications, the relative magnetic permeability values are negative, because they are found just above the resonance of the metamaterial. This thesis investigates several antenna applications of artificial magnetic materials (AMMs). The initial work is devoted to the design of a spiral resonator (SR) AMM slab to realise a low profile reflector dipole antenna by taking advantage of its PMC response. The spiral resonator has been used due to its reduced unit cell size when compared to other metamaterial resonators, leading to a more homogeneous metamaterial structure. In addition, a bidirectional PMC spacer has been applied to produce a small and compact antenna system composed of two monopole antennas, although the concept may be applied to other antenna types. A third application as an AMC reflector are the transpolarising surfaces, where the incident electric field plane wave is reflected at a polarisation rotation angle of 90 degrees. Such surfaces may be of interest to produce high cross-polar response reflecting devices, like the modified trihedral corner reflector that has been tested for polarimetric synthetic aperture radar (PolSAR) purposes. Another application of the SR AMM metamaterial is the patch antenna with a magneto-dielectric loading. The relative magnetic permeability of the AMM meta- i material has values over the unity in the frequency band below the resonance. As a consequence, the patch antenna can be miniaturised without reducing its bandwidth of operation, in contrast to a typical high dielectric permittivity substrate. Finally, the SR AMM metamaterial also presents values of relative magnetic perme- ability between zero and the unity (MNZ). In such a case, the SR AMM metamaterial has been applied as an MNZ cover of a slot antenna, devoted to increasing the broadside radiated power and directivity of the antenna. ii Contents 1 Introduction 1 1.1 Motivationandthesisobjectives . ... 1 1.2 Thesisoutline................................ 2 2 MetamaterialsinAntennaEngineering 5 2.1 IntroductiontoMetamaterials . .. 5 2.2 MetamaterialsApplications . 9 2.3 MetamaterialsAppliedtoAntennas . 10 2.3.1 Metamaterials in the Antenna Environment . 10 2.3.2 MetamaterialsintheAntennaStructure . 16 2.3.3 Metamaterials in the Antenna Feeding Network . 18 2.4 ChapterConclusions ............................ 20 3 Spiral Resonators as AMMs 21 3.1 Introduction................................. 21 3.2 AMMCharacterisation. .. .. ... .. .. .. .. .. ... .. .. .. 22 3.2.1 Simplifiedmodelling . 22 3.2.2 MNGMeasurementSetup . 26 3.3 WhySpiralResonatorsasAMMs?. 30 3.4 EffectiveMediumApproach . 36 3.5 ChapterConclusions ............................ 42 4 AMMs as AMCs 43 4.1 Introduction ................................ 43 4.1.1 Single and double layer AMCs characterisation . .. 43 4.1.2 Fabricationoftheprototypes . 48 4.1.3 S-parameterMeasurement . 49 4.2 SinglelayerSRAMCasAntennaReflector . 52 4.2.1 InputImpedance .......................... 53 4.2.2 RadiationPatterns . 55 iii 4.3 Bidirectional AMCs for Compact Antenna Systems . .. 58 4.3.1 SpatialDiversityAntennaSystems . 58 4.3.2 Two-Antenna System Design and Fabrication . 59 4.3.3 Two-AntennaSystemMeasurements . 61 4.3.3.1 S-parameters ....................... 61 4.3.3.2 EnvelopeCorrelation. 62 4.3.3.3 C-parameters . 63 4.3.3.4 RadiationPatterns . 63 4.4 ChapterConclusions ............................ 65 5 AMMs for Transpolarisation 67 5.1 Introduction................................. 67 5.1.1 PrincipleofOperation . 67 5.1.2 PotentialApplications . 69 5.1.3 Transpolarisingsurfaceexamples . 71 5.2 TranspolarisationwithaSRAMMslab . 72 5.2.1 Design and simulation of a transpolarising SR surface ...... 72 5.2.2 Fabrication and measurement of a transpolarising SR surface. 75 5.3 Designofatranspolarisingsurface. .... 77 5.4 FabricationandMeasurement . 81 5.4.1 NormalIncidenceMeasurements. 81 5.4.2 ObliqueIncidenceMeasurements . 85 5.5 ApplicationtoPolSARCalibrator . 87 5.5.1 Introduction to Polarimetric Radar Calibration . ..... 87 5.5.2 TranspolarisingSurfaceDesign . 88 5.5.3 Field Measurement Results of the Transpolarising TCR ..... 89 5.5.3.1 MeasurementSetup . 89 5.5.3.2 MeasuredResults. 91 5.6 ChapterConclusions ............................ 95 6 PatchAntennaMiniaturisationwithAMMLoadings 97 6.1 Introduction................................. 97 6.2 FBWcomputationtechniques . 98 6.3 Homogeneous Substrate Patch Antenna Analysis. 102 6.3.1 Substrateparametersvariation . 104 6.3.1.1 Electricpermittivityvariation . 104 6.3.1.2 Magneticpermeabilityvariation . 106 6.3.1.3 Electric permittivity and magnetic permeability variation107 iv 6.3.2 LossesinthePatchAntennaSubstrate . 108 6.3.3 Discussion on Bandwidth and Patch Antenna Miniaturisation . 110 6.4 Patch Antennas with Dispersive Metamaterial Loadings . ....... 113 6.4.1 SRAMMDesignasaMetasubstrate . 114 6.4.2 Simulation of Patch Antennas with AMM Metasubstrates . 116 6.4.3 Fabrication of Patch Antennas with AMM Metasubstrates . 124 6.4.4 Measurement of Patch Antennas with AMM Metasubstrates . 125 6.4.4.1 RadiationEfficiency . 128 6.4.4.2 RadiationPatterns . 129 6.5 ChapterConclusions ............................ 130 7 Leaky Wave Antennas with AMM Mu-Near-Zero Slabs 133 7.1 Introduction................................. 133 7.2 MNZ slabs for broadside radiation improvement . .... 135 7.3 SlotAntennaDesignforMNZApplications. 137 7.4 FabricationoftheMNZSlotAntennaSystem . 138 7.5 MeasurementsoftheMNZAntenna. 139 7.5.1 ReturnLoss ............................. 139 7.5.2 RadiationPatterns . 140 7.6 ChapterConclusions ............................ 146 8 Conclusions 147 8.1 Mainconclusions .............................. 147 8.2 Futureresearchlines ............................ 149 A Time-Domain Gating Method 151 B List of Publications 159 C List of Acronyms 163 Bibliography 167 v vi Chapter 1 Introduction 1.1 Motivation and thesis objectives Since the end of the twentieth-century, the development of mobile communication systems has grown together with the increasing demand for Internet and localisation services (VoIP, messaging, browsing, streaming, GPS). Year by year, the electronics systems design industry has become increasingly focused on realising smaller mobile transmitting/receiving (Tx/Rx) devices, while maintaining or increasing data capacity and signal coverage. Consequently, miniaturised antennas are in increasing demand. In addition, multiple antenna systems (MIMO), which traditionally suffer from couplings between the antenna elements, are often used to improve the signal quality and coverage in complex propagation scenarios such as urban or indoor environments. Therefore, the antenna design strategies have become more complex. On the other hand, over the last decades, Metamaterials (MTMs) have caught the attention of the scientific community [1–16]. Metamaterials are basically artificially engineered materials which can provide unusual electromagnetic properties not present in nature. The