Advanced

Thick Frequency Selective Structures

Widenberg, Björn LU (2003) 37.
Abstract (Swedish)
Popular Abstract in Swedish

Denna avhandling presenterar en metod som kan hantera generella tjocka frekvensselektiva strukturer (FSS). Metoden är baserad på modanpassning och finita elementmetoden (FEM). Avhandlingen är en sammanläggningsavhandling och består av en introduktion som följs av fem vetenskapliga artiklar.



Frekvensselektiva strukturer fungerar som filter för elektromagnetiska vågor, såsom radiovågor, radarpulser och ljus. De är frirymdsfilter, som filtrerar vågor som utbreder sig fritt i luften, i motsats till andra typer av filter där signalerna (vågorna) är bundna till någon ledare, t.ex. kabel eller vågledare. Filtren är selektiva eftersom de låter signaler med vissa frekvenser passera,... (More)
Popular Abstract in Swedish

Denna avhandling presenterar en metod som kan hantera generella tjocka frekvensselektiva strukturer (FSS). Metoden är baserad på modanpassning och finita elementmetoden (FEM). Avhandlingen är en sammanläggningsavhandling och består av en introduktion som följs av fem vetenskapliga artiklar.



Frekvensselektiva strukturer fungerar som filter för elektromagnetiska vågor, såsom radiovågor, radarpulser och ljus. De är frirymdsfilter, som filtrerar vågor som utbreder sig fritt i luften, i motsats till andra typer av filter där signalerna (vågorna) är bundna till någon ledare, t.ex. kabel eller vågledare. Filtren är selektiva eftersom de låter signaler med vissa frekvenser passera, medan de stoppar signaler med andra frekvenser. Viktiga användningsområden för FSS är i radomer och avancerade reflektorantennsystem. En radom skyddar antennen mot väder och vind, men kan samtidigt utnyttjas som ett filter.



Frekvensselektiva strukturer är ofta skiktade strukturer, d.v.s. de består av ett antal lager. De FSS som behandlas i denna avhandling består av kombinationer av aperturlager och dielektriska lager. Ett aperturlager är ett metallskikt med ett periodiskt mönster av identiska hål, medan ett dielektriskt lager är ett skikt som oftast består av ett plast- eller skummaterial. Det dielektriska lagret kan också vara ett tunt limskikt mellan två lager.



Metoden, som används för att simulera FSS, bygger på modanpassning och FEM. De elektromagnetiska fälten utanför strukturen och inuti de dielektriska skikten skrivs som en summa av periodiska planvågor. Hålen i aperturlagren betraktas som korta vågledare, och fälten inuti dessa hål skrivs som en summa av vågledarmoder. Dessa moder är en speciell typ av elektromagnetiska v{aa}gor som kan utbreda sig i ett hål. De kan bestämmas numeriskt med hjälp av finita elementmetoden. Kopplingen mellan vågorna i de olika lagren bestäms av randvillkoren för de elektromagnetiska vågorna, och matematiskt beskrivs kopplingen med hjälp av matriser. Dessa matriser, spridnings- och utbredningsmatriser, kan kombineras på ett systematiskt sätt, så att en fullständig spridningsmatris för hela den frekvensselektiva strukturen erhålls.



Introduktionen till avhandlingen ger en överblick av FSS och den metod som utvecklats. Metoden illustreras med ett utförligt exempel. I den första vetenskapliga artikeln utvecklas metoden för ett aperturlager, och den verifieras genom jämförelse med mätdata. Den andra artikeln vidareutvecklar metoden till generella FSS, och där jämförs den med beräkningar utförda av andra. Den tredje artikeln behandlar FSS med ohmska förluster i de dielektriska materialen och i den metalliska skivan. I de flesta fall är förluster en oönskad effekt. En annan oönskad effekt är störningar i filtrets egenskaper p.g.a. avvikelser i hålens placering och form. Denna effekt behandlas i den fjärde artikeln. Den sista vetenskapliga artikeln ger en lösning på ett problem som uppträder i byggnader med energifönster. Dessa fönster är nämligen ogenomträngliga för mobiltelefonsignaler. Lösningen är FSS. (Less)
Abstract
This thesis presents a new method that can handle a general thick Frequency Selective Structure (FSS), that consists of an arbitrary number of aperture layers and dielectric layers. The method is based on the Mode Matching Technique (MMT) and the finite element method (FEM). The thesis consists of a General Introduction and five scientific papers.



The General Introduction gives an overview of filters and FSS. Some applications of FSS are studied, e.g. low observable radomes and reflector antenna systems, and the MMT is described. An example of an FSS is studied in detail, where the reflection and transmission curves are depicted, and the internal mode coefficients and fields are plotted.



Paper I treats... (More)
This thesis presents a new method that can handle a general thick Frequency Selective Structure (FSS), that consists of an arbitrary number of aperture layers and dielectric layers. The method is based on the Mode Matching Technique (MMT) and the finite element method (FEM). The thesis consists of a General Introduction and five scientific papers.



The General Introduction gives an overview of filters and FSS. Some applications of FSS are studied, e.g. low observable radomes and reflector antenna systems, and the MMT is described. An example of an FSS is studied in detail, where the reflection and transmission curves are depicted, and the internal mode coefficients and fields are plotted.



Paper I treats a perfectly conducting thick screen perforated with a periodic array of apertures with arbitrary cross-section. The scattered fields are determined by the MMT. Excellent agreement between computed and measured transmission is found. The present method and the spectral Galerkin method are compared for very thin perforated screens. The transmission depends on the thickness, and this dependence is investigated for a wide range of thicknesses.



Paper II introduces a method that can handle a thick FSS, that consists of an arbitrary number of aperture layers and dielectric layers. An aperture layer is a conducting plate with a periodic array of apertures. The periodicity in the different layers must be in accord. The layers can be of any thickness and in any order, and the cross-section of the apertures is arbitrary.



Paper III analyzes dissipation in FSS of aperture/slot type. The dissipation in an FSS is due to losses in the dielectric material, and losses due to finite conductivity in the metallic plate. The dissipation on the metallic structure arises both on the plane metallic surface and on the metallic walls of the apertures. The attenuation and the power losses are calculated for a number of different FSS. Based on these results the performance of an FSS with losses is discussed.



Paper IV deals with the performance of an FSS with defects. In this case the structure is a periodic pattern of apertures in a conducting plate. The defects can be deviations in the placing of the apertures, in the material parameters, or in the shape of the apertures. First the perturbation to the farfield pattern from a deviation in one aperture is analyzed. This is then utilized for a statistical analysis of an FSS with a stochastic variation of the apertures.



Paper V focuses on the radio wave propagation through energy saving windows. These panes have a metallic shielding that keeps the heat inside the building during winter and outside the building during summer. Unfortunately, this covering also has an opaque behaviour at microwave frequencies. A design of energy saving window panes with high transmission at 900 MHz and 1800 MHz is presented. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Doc Norgren, Martin, Alfvénlaboratory, KTH, Stockholm
organization
publishing date
type
Thesis
publication status
published
subject
keywords
acoustics, Elektromagnetism, optik, akustik, optics, Electromagnetism, Energy Saving Window, Radome, Finite Elemente Method, Frequency Selective Structure, Mode Matching Technique
volume
37
pages
198 pages
publisher
Department of Electroscience, Lund University
defense location
Room E:1406, E-building, Lund Institute of Technology
defense date
2003-06-05 10:15
ISSN
1402-8662
language
English
LU publication?
yes
id
5322be56-e10b-4c36-99b6-5eb65bcd6389 (old id 465968)
date added to LUP
2007-09-10 15:56:57
date last changed
2016-09-19 08:44:59
@phdthesis{5322be56-e10b-4c36-99b6-5eb65bcd6389,
  abstract     = {This thesis presents a new method that can handle a general thick Frequency Selective Structure (FSS), that consists of an arbitrary number of aperture layers and dielectric layers. The method is based on the Mode Matching Technique (MMT) and the finite element method (FEM). The thesis consists of a General Introduction and five scientific papers.<br/><br>
<br/><br>
The General Introduction gives an overview of filters and FSS. Some applications of FSS are studied, e.g. low observable radomes and reflector antenna systems, and the MMT is described. An example of an FSS is studied in detail, where the reflection and transmission curves are depicted, and the internal mode coefficients and fields are plotted.<br/><br>
<br/><br>
Paper I treats a perfectly conducting thick screen perforated with a periodic array of apertures with arbitrary cross-section. The scattered fields are determined by the MMT. Excellent agreement between computed and measured transmission is found. The present method and the spectral Galerkin method are compared for very thin perforated screens. The transmission depends on the thickness, and this dependence is investigated for a wide range of thicknesses.<br/><br>
<br/><br>
Paper II introduces a method that can handle a thick FSS, that consists of an arbitrary number of aperture layers and dielectric layers. An aperture layer is a conducting plate with a periodic array of apertures. The periodicity in the different layers must be in accord. The layers can be of any thickness and in any order, and the cross-section of the apertures is arbitrary.<br/><br>
<br/><br>
Paper III analyzes dissipation in FSS of aperture/slot type. The dissipation in an FSS is due to losses in the dielectric material, and losses due to finite conductivity in the metallic plate. The dissipation on the metallic structure arises both on the plane metallic surface and on the metallic walls of the apertures. The attenuation and the power losses are calculated for a number of different FSS. Based on these results the performance of an FSS with losses is discussed.<br/><br>
<br/><br>
Paper IV deals with the performance of an FSS with defects. In this case the structure is a periodic pattern of apertures in a conducting plate. The defects can be deviations in the placing of the apertures, in the material parameters, or in the shape of the apertures. First the perturbation to the farfield pattern from a deviation in one aperture is analyzed. This is then utilized for a statistical analysis of an FSS with a stochastic variation of the apertures.<br/><br>
<br/><br>
Paper V focuses on the radio wave propagation through energy saving windows. These panes have a metallic shielding that keeps the heat inside the building during winter and outside the building during summer. Unfortunately, this covering also has an opaque behaviour at microwave frequencies. A design of energy saving window panes with high transmission at 900 MHz and 1800 MHz is presented.},
  author       = {Widenberg, Björn},
  issn         = {1402-8662},
  keyword      = {acoustics,Elektromagnetism,optik,akustik,optics,Electromagnetism,Energy Saving Window,Radome,Finite Elemente Method,Frequency Selective Structure,Mode Matching Technique},
  language     = {eng},
  pages        = {198},
  publisher    = {Department of Electroscience, Lund University},
  school       = {Lund University},
  title        = {Thick Frequency Selective Structures},
  volume       = {37},
  year         = {2003},
}