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Twist and Polar Glide Symmetries: an Additional Degree of Freedom to Control the Propagation Characteristics of Periodic Structures
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.ORCID iD: 0000-0001-9241-8030
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.ORCID iD: 0000-0002-4900-4788
2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8Article in journal, Editorial material (Refereed) Published
Abstract [en]

New high-frequency 5G and satellite communication systems require fully-metallic antennas and electromagnetic components. These components can be implemented with truncated versions of periodic structures. In order to achieve the desired performance of these future devices, it is of crucial importance to have a precise control of the propagation properties, i.e. the frequency dispersion behavior and stop-bands. Here, we demonstrate the potential use of higher symmetries to diminish the frequency dispersion of periodic structures and control the width of stop-bands with a new type of fully-metallic transmission line, which is loaded with holes on a twist-symmetric configuration. Simulated and experimental results confirm the intrinsic link between the propagation characteristics and the symmetries of a periodic structure. Additionally, we provide a definitive explanation of the recently discovered polar glide symmetry and its potential combination with twist symmetries to produce low-dispersive materials and reconfigurable stop-bands. The promising properties of these structures are demonstrated with a fully-metallic reconfigurable filter, which could be used for future high-frequency 5G and satellite communication systems.

Place, publisher, year, edition, pages
2018. Vol. 8
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-239132DOI: 10.1038/s41598-018-29565-6ISI: 000439805700027Scopus ID: 2-s2.0-85050674647OAI: oai:DiVA.org:kth-239132DiVA, id: diva2:1263722
Note

QC 20181120

Available from: 2018-11-16 Created: 2018-11-16 Last updated: 2019-05-20Bibliographically approved
In thesis
1. Periodic Structures with Higher Symmetries: Analysis and Applications
Open this publication in new window or tab >>Periodic Structures with Higher Symmetries: Analysis and Applications
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, periodic structures with higher symmetries are studied. Their wave propagation characteristics are investigated and their potential applications are discussed. 

Higher-symmetric periodic structures are described with an additional geometrical operation beyond a translation operator. Two particular types of higher symmetry are glide and twist symmetries. Glide-symmetric periodic structures remain invariant under a translation of half a period followed by a reflection with respect to a glide plane. Twist-symmetric periodic structures remain invariant under a translation along followed by a rotation around a twist axis. 

In a periodic structure with a higher symmetry, in which the higher order modes are excited, the frequency dispersion of the first mode is dramatically reduced. This feature overcomes the bandwidth limitations of conventional periodic structures. Therefore, higher-symmetric periodic structures can be employed for designing wideband metasurface-based antennas. For example, holey glide-symmetric metallic structures can be used to design low loss, wideband flat Luneburg lens antennas at millimeter waves, which find application in 5G communication systems. In addition, holey glide-symmetric structures can be exploited as low cost electromagnetic band gap (EBG) structures at millimeter waves, due to a wider stop-band achievable compared to non-glide-symmetric surfaces. 

However, these attractive dispersive features can be obtained if holey surfaces are strongly coupled, so higher-order modes produce a considerable coupling between glide-symmetric holes. Hence, these structures cannot be analyzed using common homogenization methods based on the transverse resonance method. Thus, in this thesis, a mode matching formulation, taking the generalized Floquet theorem into account, is applied to analyze glide-symmetric holey periodic structures with arbitrary shape of the hole. Applying the generalized Floquet theorem, the computational domain is reduced to half of the unit cell. The method is faster and more efficient than the commercial software such as CST Microwave Studio. In addition, the proposed method provides a physical insight about the symmetry of Floquet modes propagating in these structures. 

Moreover, in this thesis, the effect of twist symmetry and polar glide symmetry applied to a coaxial line loaded with holes is explained. A rigorous definition of polar glide symmetry, which is equivalent to glide symmetry in a cylindrical coordinate, is presented. It is demonstrated that the twist and polar glide symmetries provide an additional degree of freedom to engineer the dispersion characteristics of periodic structures. In addition, it is demonstrated that the combination of these two symmetries provides the possibility of designing reconfigurable filters. Finally, mimicking the twist symmetry effect in a flat structure possessing glide symmetry is investigated. The results demonstrate that the dispersion properties associated with twist symmetry can be mimicked in flat structures.

 

Abstract [sv]

Denna avhandling behandlar periodiska strukturer med högre symmetrier. Deras vågutbredningsegenskaper undersöks och deras potentiella tillämpningar diskuteras.

Periodiska strukturer med högre symmetrier beskrivs med ytterligare en geometrisk operator, utöver den translationsoperator. Två specialfall av högre symmetrier är glid- och vridsymmetrier. Glidsymmetriska periodiska strukturer är invarianta under en translation (glidning) på en halvperiod följt av en reflektion med avseende på ett glidplan. Vridsymmetriska periodiska strukturer är invarianta under en translation längs med följt av en rotation kring en vridningsaxel.

I en högsymmetrisk periodisk struktur, innehrillande flera högre ordningens moder, fås en dramatisk minskning av frekvensdispersionen för den första moden, varigenom den bandbreddsbegränsning som finns i konventionella periodiska strukturer kan övervinnas. Därigenom kan högsymmetriska strukturer användas vid utformandet av bredbandiga antenner baserade på metaytor. Till exempel kan urkärnade glidsymmetriska metallstrukturer användas för att utforma bredbandiga Luneburg-linser med låga förluster, vilka för millimetervågor har tillämpningar inom femte generationens kommunikationssystem (5G). Dessutom kan dessa strukturer utnyttjas som kostnadseffektiva elektromagnetiska bandgap (EBG)-strukturer för millimetervågor.

På grund av förekomsten av högre ordningens moder kan emellertid inte högsymmetriska periodiska strukturer med starkt kopplade skikt analyseras med användning av den konventionella transversella resonansmetoden. Därför används i denna avhandling en modanpassningsmetod, vars formulering bygger på den generaliserade versionen av Floquets teorem, för att analysera glidsymmetriska urkärnade periodiska strukturer där hålen har godtyckligt tvärsnitt. Användingen av Floquets generaliserade teorem halverar storleken på beräkningsdomänen och metoden är både snabbare och effektivare än kommersiella programvaror som CST Microwave Studio. Dessutom bidrar den föreslagna metoden till fysikalisk förståelse genom symmetriegenskaperna hos de Floquet-moder som utbreder sig i de högsymmetriska strukturerna.

Vidare definieras polär glidssymmetri, som motsvarar glidsymmetri i ett cylindriskt koordinatsystem, och en förklaring ges hur den tillsammans med vridsymmetri kan tillämpas på koaxiella strukturer. Det visas att vrid- och polärglidssymmetrier ger ytterligare en frihetsgrad vid utformandet av dispersionsegenskaperna hos periodiska strukturer. Dessutom demonstreras att kombinationen av dessa två symmetrier ger möjligheten att designa omkonfigurerbara filter. Slutligen visas att dispersionsegenskaperna associerade med vridsymmetri kan efterliknas i plana strukturer.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 52
Series
TRITA-EECS-AVL ; 2018:92
Keywords
periodic structures, higher symmetries, dispersion analysis, mode matching, generalized Floquet theorem
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-239141 (URN)978-91-7873-035-3 (ISBN)
Public defence
2018-12-14, Kollegiesalen, Brinellvägen 8, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20181119

Available from: 2018-11-19 Created: 2018-11-16 Last updated: 2018-11-19Bibliographically approved

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