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Radome Diagnostics: utilizing Source Reconstruction based on Surface Integral Representations

Persson, Kristin LU (2013) In Series of licentiate and doctoral theses 49.
Abstract
In this thesis, an inverse source reconstruction method with great potential in radome diagnostics is presented. A radome is a cover that encloses an antenna in order to protect it from environmental influences. Radome diagnostics are acquired in the design process, the delivery control, and in performance verification of repaired and newly developed radomes. A measured near or far field may indicate deviations, e.g., beam deflection, but the origins of the flaws are not uncovered. In this thesis, radome diagnostics is performed by imaging the tangential electromagnetic fields on radome surfaces, disclosing the radome influence on the electromagnetic fields as well as the positions and influences of defects.



The source... (More)
In this thesis, an inverse source reconstruction method with great potential in radome diagnostics is presented. A radome is a cover that encloses an antenna in order to protect it from environmental influences. Radome diagnostics are acquired in the design process, the delivery control, and in performance verification of repaired and newly developed radomes. A measured near or far field may indicate deviations, e.g., beam deflection, but the origins of the flaws are not uncovered. In this thesis, radome diagnostics is performed by imaging the tangential electromagnetic fields on radome surfaces, disclosing the radome influence on the electromagnetic fields as well as the positions and influences of defects.



The source reconstruction is based on a surface integral representation together with the extinction theorem. The extinction theorem and its associated surface integral equation ensure that the reconstructed tangential electromagnetic fields have their sources within the radome. The presence of axial symmetry in the measurement set-up enables usage of the fast Fourier transform to reduce the computational complexity. Furthermore, the problem is solved by an in-house body of revolution method of moments (MoM) code utilizing a singular value decomposition (SVD) for regularization. The reconstruction is performed on a fictitious surface in free space, located precisely outside the physical surface of the radome, i.e., no a priori information of the material of the radome is requested. Moreover, both synthetic and measured data are used to verify the method.



In Papers I-III, the measurement set-up is a reflector antenna covered by a monolithic radome, and the near field is measured on a cylindrical surface. The height of the radome corresponds to 29-43 wavelengths in the frequency interval 8.0-12.0 GHz. The amplitude and phase of the tangential electromagnetic fields are reconstructed on the radome surface and the influence of the radome is investigated. Moreover, the alteration of the phase due to the transmission of the radome, the insertion phase delay (IPD), is imaged. Defects in the form of square copper patches, with an edge length corresponding to 1.6-2.4 wavelengths in the considered frequency interval, are attached to the radome wall. These might serve as a model for e.g., a lightning conductor or a Pitot tube. The attached patches alter the near field, and by applying source reconstruction, the disturbances of the patches are focused and detectable.



In Paper IV, the field is measured on a spherical sector in the far-field region at 10.0 GHz. Two set-ups with dielectric defects attached to the radome surface, are investigated. The aim is to investigate if variations in the electrical thickness of the radome wall can be detected. It is concluded that it is possible to discover dielectric patches of various edge sizes (0.5-2.0 wavelengths), and with the smallest thickness corresponding to a phase shift of a couple of degrees.



In Paper V, a frequency selective (FSS) radome corresponding to a height of 51 wavelengths at the frequency 9.35 GHz is investigated. The electrical performance of an FSS radome depends on the periodic structure of the elements in the radome frame. The periodic structure of the investigated radome is disrupted by horizontal defects (vertical displacements of elements) and vertical defects (a column of missing elements). The far-field data is measured on a spherical sector, and the far-field data reveals that the radome changes the radiation properties. The tangential electromagnetic fields on the radome surface are reconstructed for several antenna illuminations to image the cause of these alterations. Furthermore, it is shown that the different components of the electromagnetic fields are affected differently by the defects, implying that both co- and cross-components of the electric and magnetic fields need to be considered. Moreover, the Poynting's vector is employed to visualize how the defects block the field from the antenna. (Less)
Abstract (Swedish)
Popular Abstract in Swedish

Elektromagnetiska fält finns idag överallt och är en förutsättning för att det moderna samhället ska fungera. Utan att fundera närmare på det, använder vi oss ständigt av de elektromagnetiska fältens förmåga att trådlöst överföra information och energi. Några exempel är; uppvärmning av mat i mikron och på induktionshällen, samtal i mobiltelefonen, uppdatering av status på Facebook oavsett var vi befinner oss, samt volyminställning på TV och stereo med fjärrkontrollen.

För att omvandla en elektrisk ström i en apparat till elektromagnetiska fält som breder ut sig i luften, eller tvärt om, används antenner. En antenn kan behöva skyddas från väderpåverkan och insyn. Ett sådant skydd kallas... (More)
Popular Abstract in Swedish

Elektromagnetiska fält finns idag överallt och är en förutsättning för att det moderna samhället ska fungera. Utan att fundera närmare på det, använder vi oss ständigt av de elektromagnetiska fältens förmåga att trådlöst överföra information och energi. Några exempel är; uppvärmning av mat i mikron och på induktionshällen, samtal i mobiltelefonen, uppdatering av status på Facebook oavsett var vi befinner oss, samt volyminställning på TV och stereo med fjärrkontrollen.

För att omvandla en elektrisk ström i en apparat till elektromagnetiska fält som breder ut sig i luften, eller tvärt om, används antenner. En antenn kan behöva skyddas från väderpåverkan och insyn. Ett sådant skydd kallas radom och sitter som ett hölje över antennen. Ett exempel på en radom är noskonen på ett flygplan.

Radomen ska helst vara elektriskt genomskinlig, det vill säga den ska inte förändra de elektromagnetiska fälten som antennen skickar ut eller tar emot. Elektrisk genomskinlighet är dock mycket svårt att uppnå eftersom det är många faktorer som man måste ta hänsyn till vid radomtillverkningen. En noskon på ett flygplan är t.ex. väldigt utsatt där den sitter längst fram. Radomen måste vara robust för att stå emot kraftiga mekaniska påfrestningar såsom regn- och hagelstormar, samtidigt som den inte ska vara alltför tung. Flygplanets hastighetsmätare sitter oftast som ett metallrör längst fram i radomens nos. Detta rör attraherar blixten, vilket betyder att ett kraftigt blixtskydd är nödvändigt. Dessutom ska radomen även vara aerodynamiskt utformad. Alla dessa krav på radomen går inte att till fullo uppfylla samtidigt. Detta innebär att den elektriska genomskinligheten kommer att påverkas, det vill säga, radomen kommer till viss del att påverka och förändra antennens elektriska prestanda.

Innan leverans av nya radomer, samt vid tester på lagade radomer, genomförs oftast fjärrfältsmätningar för att avgöra om uppsatta specifikationer uppnås. Med hjälp av fjärrfältsdata kan man se om något är fel men inte vad felet beror på. För att hitta orsaken till felet måste ytterligare undersökningar göras. Exempelvis kan man undersöka om det elektromagnetiska fältets fas påverkas som det är tänkt då fältet passerar genom radomväggen. En annan metod som används för att t.ex. hitta sprickor i radomväggen är ultraljud. I denna avhandling föreslås ett nytt sätt att diagnostisera radomer. Metoden är baserad på källrekonstruktion vilket innebär att ett uppmätt elektromagnetiskt fält "backas tillbaka" till radomytan. Genom att åskådliggöra fälten på den tredimensionella radomkroppen kan defekter lokaliseras och deras inverkan på de elektromagnetiska fälten kan studeras. Resultaten är mycket positiva och metoden har stor potential att kunna utvecklas till ett industriellt anpassat diagnostiseringsverktyg. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Cheney, Margaret, Department of Electrical and Computer Engineering, Colorado State University, USA.
organization
alternative title
Radomdiagnostik – källrekonstruktion baserad på ytintegralrepresentationer
publishing date
type
Thesis
publication status
published
subject
keywords
nondestructive testing, source reconstruction, diagnostics, radome, phase reconstruction, insertion phase delay (IPD), equivalent surface currents
in
Series of licentiate and doctoral theses
volume
49
pages
170 pages
publisher
Department of Electrical and Information Technology, Lund University
defense location
Lecture hall E:1406, E-building, Ole Römers väg 3, Lund University Faculty of Engineering
defense date
2013-06-14 10:15:00
ISSN
1654-790X
ISBN
978-91-7473-524-6
978-91-7473-523-9
language
English
LU publication?
yes
id
106d9401-defa-43fa-badc-d332c3c978de (old id 3738248)
date added to LUP
2016-04-01 15:01:48
date last changed
2019-05-24 08:42:23
@phdthesis{106d9401-defa-43fa-badc-d332c3c978de,
  abstract     = {{In this thesis, an inverse source reconstruction method with great potential in radome diagnostics is presented. A radome is a cover that encloses an antenna in order to protect it from environmental influences. Radome diagnostics are acquired in the design process, the delivery control, and in performance verification of repaired and newly developed radomes. A measured near or far field may indicate deviations, e.g., beam deflection, but the origins of the flaws are not uncovered. In this thesis, radome diagnostics is performed by imaging the tangential electromagnetic fields on radome surfaces, disclosing the radome influence on the electromagnetic fields as well as the positions and influences of defects.<br/><br>
<br/><br>
The source reconstruction is based on a surface integral representation together with the extinction theorem. The extinction theorem and its associated surface integral equation ensure that the reconstructed tangential electromagnetic fields have their sources within the radome. The presence of axial symmetry in the measurement set-up enables usage of the fast Fourier transform to reduce the computational complexity. Furthermore, the problem is solved by an in-house body of revolution method of moments (MoM) code utilizing a singular value decomposition (SVD) for regularization. The reconstruction is performed on a fictitious surface in free space, located precisely outside the physical surface of the radome, i.e., no a priori information of the material of the radome is requested. Moreover, both synthetic and measured data are used to verify the method.<br/><br>
<br/><br>
In Papers I-III, the measurement set-up is a reflector antenna covered by a monolithic radome, and the near field is measured on a cylindrical surface. The height of the radome corresponds to 29-43 wavelengths in the frequency interval 8.0-12.0 GHz. The amplitude and phase of the tangential electromagnetic fields are reconstructed on the radome surface and the influence of the radome is investigated. Moreover, the alteration of the phase due to the transmission of the radome, the insertion phase delay (IPD), is imaged. Defects in the form of square copper patches, with an edge length corresponding to 1.6-2.4 wavelengths in the considered frequency interval, are attached to the radome wall. These might serve as a model for e.g., a lightning conductor or a Pitot tube. The attached patches alter the near field, and by applying source reconstruction, the disturbances of the patches are focused and detectable. <br/><br>
<br/><br>
In Paper IV, the field is measured on a spherical sector in the far-field region at 10.0 GHz. Two set-ups with dielectric defects attached to the radome surface, are investigated. The aim is to investigate if variations in the electrical thickness of the radome wall can be detected. It is concluded that it is possible to discover dielectric patches of various edge sizes (0.5-2.0 wavelengths), and with the smallest thickness corresponding to a phase shift of a couple of degrees.<br/><br>
<br/><br>
In Paper V, a frequency selective (FSS) radome corresponding to a height of 51 wavelengths at the frequency 9.35 GHz is investigated. The electrical performance of an FSS radome depends on the periodic structure of the elements in the radome frame. The periodic structure of the investigated radome is disrupted by horizontal defects (vertical displacements of elements) and vertical defects (a column of missing elements). The far-field data is measured on a spherical sector, and the far-field data reveals that the radome changes the radiation properties. The tangential electromagnetic fields on the radome surface are reconstructed for several antenna illuminations to image the cause of these alterations. Furthermore, it is shown that the different components of the electromagnetic fields are affected differently by the defects, implying that both co- and cross-components of the electric and magnetic fields need to be considered. Moreover, the Poynting's vector is employed to visualize how the defects block the field from the antenna.}},
  author       = {{Persson, Kristin}},
  isbn         = {{978-91-7473-524-6}},
  issn         = {{1654-790X}},
  keywords     = {{nondestructive testing; source reconstruction; diagnostics; radome; phase reconstruction; insertion phase delay (IPD); equivalent surface currents}},
  language     = {{eng}},
  publisher    = {{Department of Electrical and Information Technology, Lund University}},
  school       = {{Lund University}},
  series       = {{Series of licentiate and doctoral theses}},
  title        = {{Radome Diagnostics: utilizing Source Reconstruction based on Surface Integral Representations}},
  url          = {{https://lup.lub.lu.se/search/files/4305831/3738261.pdf}},
  volume       = {{49}},
  year         = {{2013}},
}