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On the Accuracy of Equivalent Antenna Representations
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.ORCID iD: 0000-0003-1465-3566
Saab Surveillance.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The accuracy of two equivalent antenna representations, near-field sources and far-field sources, are evaluated for an antenna installed on a simplified platform in a series of case studies using different configurations of equivalent antenna representations. The accuracy is evaluated in terms of installed far-fields and surface currents on the platform. The results show large variations between configurations. The root-mean-square installed far-field error is 4.4 % for the most accurate equivalent representation. When using far-field sources, the design parameters have a large influence of the achieved accuracy. There is also a varying accuracy depending on the type of numerical method used. Based on the results, some recommendations on the choice of sub-domain for the equivalent antenna representation are given. In industrial antenna applications, the accuracy in determining e.g. installed far-fields and antenna isolation on large platformsare critical. Equivalent representations can reduce the fine-detail complexity of antennas and thus give an efficient numerical descriptions to be used in large-scale simulations. The results in this paper give valuable information to antenna designers and system engineers about the expected errors introduced when using equivalent antenna representations.

Keyword [en]
Antenna modeling, Computational electromagnetics, Electromagnetic analysis, Electromagnetic modeling
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-215195OAI: oai:DiVA.org:kth-215195DiVA: diva2:1146931
Note

QC 20171010

Available from: 2017-10-04 Created: 2017-10-04 Last updated: 2017-10-10Bibliographically approved
In thesis
1. Efficient Methods to Calculate Mutual Coupling between Generic Antennas on Large Platforms
Open this publication in new window or tab >>Efficient Methods to Calculate Mutual Coupling between Generic Antennas on Large Platforms
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents research on methods for calculating the mutual coupling between antennas. The mutual coupling between antennas is a measure of the amount of energy transmitted from one antenna that is received by another, and is a key parameter when installing antennas on platforms, such as aircraft. To avoid interference between systems connected to the antennas, the mutual coupling should be as low as possible. The risk for interference can be minimized in several ways; by designing the systems to be resistant to interference or to install the antennas in a way that makes the coupling between antennas low. This thesis focuses on the latter.

Electromagnetic problems, such as finding the mutual coupling between antennas, can be calculated in simulations using commercial software. On large platforms, simulations become very computationally intensive. This thesis examines ways to efficiently calculate the mutual coupling between antennas on large platforms. The intention has been to develop methods that can be used in practical situations.

One possible way to increase efficiency is to use appropriate approximations that simplify calculations. Two approximations have been evaluated; approximate wave propagation model and equivalent representations of antennas. Both of these approximations have the potential to reduced computation times, but suffer from the fact that the size of the errors introduced is not predictable. This contributes to an uncertainty in estimating the coupling between antennas that make them less interesting to use in applications. The reaction theorem, that describes the coupling as an interaction of electromagnetic fields, has been very useful in this work. Two novel formulations of the theorem have been derived that decompose fields into scattered components. It is shown that some of the components do not affect the reaction. The reaction theorem and the derived formulations have been used in two applications. The first application shows practical possibilities to calculate mutual impedance between two antennas installed on a common platform. It is also shown how the reaction theorem can be used to visualize coupling paths, which show how the coupling between the antennas is spatially distributed.

The second application of the reaction theorem suggests an effective method for antenna placement on platforms that minimize the mutual impedance between antennas. The method enables field data to be reused, which significantly reduces the calculation time. Both suggested applications post-process electromagnetic field data. The field data can be determined with commercial software.

The main results in this thesis are described in five articles and conference contributions that are or will be published in international scientific journals or at international conferences.

Abstract [sv]

Denna avhandling behandlar metoder för att beräkna ömsesidig koppling mellan antennar. Den ömsesidiga kopplingen beskriver hur mycket av den energi som sänds ut i en av antennerna som tas upp av den andra antennen och är ett viktigt mätetal vid installation av antenner på plattformar, såsom flygplan. För att undvika störningar mellan de system som ansluts till antennerna så bör kopplingen vara så låg som möjligt. Risken för störning påverkas av både de system som ansluts till antennerna och utbredningsvägen mellan antennerna. Denna avhandling fokuserar på det senare.

Elektromagnetiska problem, t ex koppling mellan antenner, löses standardmässigt genom simuleringar med kommersiella programvaror. Simuleringarna blir dock mycket beräkningsintensiva för stora plattformar. Avhandling undersöker sätt att effektivt beräkna kopplingen. Syftet med arbetet har varit att ta fram metoder som kan användas i praktiska situationer.  

En möjlig effektivisering är att införa approximationer som bidrar till att förenkla beräkningarna. Två typer av approximationer har undersökts, dels förenklade vågutbredningsmodeller och dels ekvivalenta representationer av antenner. Båda dessa approximationer har potential att ge minskade beräkningstider men lider av att storleken på felen som introduceras inte är predikterbara. Detta bidrar till en osäkerhet vid uppskattning av kopplingen mellan antenner som gör dem mindre intressanta att använda i tillämpningar.  

Reaktionsteoremet, som beskriver hur kopplingen förmedlas via elektromagnetiska fält, har visat sig mycket användbart i detta arbete. För att kunna tillämpa det så har två nya formuleringar av teoremet härletts. Formuleringarna delar upp genererade fält i dess spridda komponenter och visar att vissa komponenter inte påverkar reaktionen. Reaktionsteoremet och de härledda formuleringarna används i två tillämpningar.  

Den första tillämpningen visar på praktiska möjligheter att beräkna ömsesidiga impedansen mellan antenner på en gemensam plattform. Det visas även på en metod för att visualisera kopplingsvägar, något som ger viktig information om hur kopplingen mellan antennerna är spatialt fördelad.  

Den andra tillämpningen som använder reaktionsteoremet föreslår en effektiv metod för att placera antenner på en plattform så att den ömsesidiga impedansen mellan antennerna minimeras. Metoden används som ett efterbehandlingssteg där indata är fältvärden beräknade med kommersiell mjukvara. Metoden möjliggör att beräknade fältdata kan återanvändas vilket signifikant minskar beräkningstiden.  

De huvudsakliga resultaten från avhandlingen är samlade i totalt fem artiklar och konferensbidrag som har eller ska publiceras i internationella vetenskapliga tidskrifter eller på konferenser. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 63 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2017:086
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-215241 (URN)978-91-7729-485-6 (ISBN)
Presentation
2017-10-26, Q2, Kungl Tekniska högskolan, Osquldas väg 10, Stockholm, 09:45
Opponent
Supervisors
Note

QC 20171005

Available from: 2017-10-05 Created: 2017-10-05 Last updated: 2017-10-31Bibliographically approved

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