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Physical limitations of phased antenna arrays
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.ORCID iD: 0000-0002-7057-6414
KTH, School of Electrical Engineering and Computer Science (EECS).ORCID iD: 0000-0003-4746-3160
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.ORCID iD: 0000-0001-7269-5241
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this paper, the bounds on the Q-factor, a quantity inversely proportional to bandwidth, for phased antenna arrays are derived and investigated. Arrays in free space and above a ground plane are considered. The bounds are determined by optimizing the Q-factor represented in terms of electric current density on a unit-cell element. The optimization problem is formulated as a QCQP minimization of the Q-factor over all possible current densities on an enclosing element shape in a unit cell environment. The constraints can include conductive losses and polarization purity. We demonstrate how such bounds can be used to build Pareto-type trade-off relations between the Q-factor and other design specifications: element form-factor and size, efficiency and polarization purity.

Keywords [en]
Q-factor, stored energy, fundamental bounds, optimization, QCQP
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-266700OAI: oai:DiVA.org:kth-266700DiVA, id: diva2:1386189
Funder
Swedish Foundation for Strategic Research , AM13-0011Vinnova, ChaseOn/iAA
Note

QC 20200117

Available from: 2020-01-16 Created: 2020-01-16 Last updated: 2020-01-17Bibliographically approved
In thesis
1. Fundamental Bounds on Performance of Periodic Electromagnetic Radiators and Scatterers
Open this publication in new window or tab >>Fundamental Bounds on Performance of Periodic Electromagnetic Radiators and Scatterers
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, the optimal bandwidth performance of periodic electromagnetic radiators and scatterers is studied. The main focus is on the development and application of methods to obtain fundamental physical bounds, relating geometrical parameters, frequency bandwidth, efficiency and radiation characteristics of periodic electromagnetic structures.

Increasing demand on the performance of wireless electromagnetic systems in the modern world requires miniaturization, high data rates, high efficiency, and reliability in harsh electromagnetic environments. Attempts to improve all these design metrics at once confront the inevitable physical limitations. For example, an antenna’s size is fundamentally bounded with bandwidth performance, and attempts to decrease size result in reduced performance capabilities. Knowledge of such physical bounds is vital to achieve high performance: to gain an understanding of the trade-off between parameters and requirements, or to evaluate how optimal the realized design is.

Periodic structures are indispensable components in many wireless systems. As antenna arrays, they are in base stations of mobile phone networks, in radio astronomy, in navigation systems. As functional structures, they are used as frequency-selective filters, polarizers and metamaterials.

In this thesis, methods to construct fundamental bounds on Q-factor – a quantity inversely proportional to bandwidth – are presented for periodic structures. First, the Q-factor representation is derived in terms of the electric current density in a unit cell. Then, the bounds are obtained by minimizing the Q-factor over all current densities, that are supported in a specified spatial subset of a unit cell, with possibly additional constraints (e.g. on conductive losses, or on polarization) imposed.

Moreover, an alternative approach for obtaining fundamental bandwidth bounds is investigated – the sum rules, that are based on representing a physical phenomenon as a passive input-output system. Transmission of a plane wave through a periodically perforated metal screen is described by a passive system, and the sum rule bounds the transmission bandwidth with the static polarizability of the unit cell. Such a bound is shown to be tight for simulated and measured perforated screens.

Abstract [sv]

Den här avhandlingen undersöker den optimala prestandan av elektromagnetiska periodiska radiatorer och spridare. Huvudinriktningen är utveckling och tillämpning av metoder för att erhålla fundamentala fysikaliska begränsningar, som relaterar geometriska parametrar, bandbredd, verkningsgrad/effektivitet och strålningsegenskaper av periodiska elektromagnetiska strukturer.

Ökande krav på prestanda av trådlösa elektromagnetiska system driver fram miniatyrisering, hög datahastighet och hög tillförlitlighet i robusta elektromagnetiska miljöer. Försök att förbättra alla dessa designegenskaper på en och samma gång möter oundvikliga fysikaliska begränsningar. För antenner är deras bandbredd begränsad av antennens elektriska storlek, och försök att minska storleken resulterar i minskad prestanda. Kunskap om sådana fysikaliska relationer är avgörande för att uppnå hög prestanda: att öka förståelsen för kompromisser mellan olika parametrar, eller att avgöra hur optimal konstruktionen är.

Periodiska strukturer är viktiga komponenter i många trådlösa system. Till exempel gruppantenner, som finns i basstationer för mobiltelefonnätverk, i radioastronomi och i navigationssystem. Ytterligare exempel är funktionella strukturer som används som frekvensselektiva filter och metamaterial.

I denna avhandling presenteras metoder för att erhålla begränsningar av Q-faktorn, en storhet omvänt proportionell mot bandbredden för periodiska strukturer. Först bestäms Q-faktorn i termer av ytströmstätheten i en enhetscell. Sedan bestäms begränsningar genom att minimera Q-faktorn över alla möjliga strömstätheter i en delmängd av en enhetscell, med möjligtvis ytterligare restriktioner (t. ex. resistiva förluster).

I denna avhandling kommer även ett alternativt förhållningssätt för att uppnå fundamentala bandbredds begränsningar att undersökas – summaregler, baserade på att framställa ett fysikaliskt fenomen som ett passivt input-outputsystem. En överföring av en våg genom en periodiskt perforerad metallskärm beskrivs av ett passivt system, och summareglen begränsar bandbredden med enheltscellens statiska polariserbarhet. En sådan begränsning visar sig vara skarp för några simulerade och uppmätta perforerade skärmar.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2020. p. 64
Series
TRITA-EECS-AVL ; 2020:8
Keywords
Q-factor, bandwidth, antenna arrays, periodic structures, physical bounds, physical limitations
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-266703 (URN)978-91-7873-413-9 (ISBN)
Public defence
2020-02-07, Kollegiesalen, Brinellvägen 8, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , AM13-0011Vinnova, ChaseOn/iAA
Available from: 2020-01-17 Created: 2020-01-16 Last updated: 2020-01-17Bibliographically approved

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Ludvig-Osipov, AndreiHannula, Jari-MattiJonsson, B. Lars G.

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