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Electromagnetic Simulation, Analysis and Design with Application to Antennas and Radar Absorbers
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis considers two different subjects in the research area of electromagnetics. The first part is concerned with antenna design and the second with radar absorbers and rasorber.

In the first part, a novel excitation technique for cylindrical dielectric resonator antennas is introduced to produce circular polarization. The exciter is a tape helix that is wound around the dielectric resonator and is fed by a coaxial probe. The helix excites the HE11σ modes in phase quadrature in the cylindrical dielectric resonator antenna. The height of the helix is determined using the Hansen-Woodyard condition for an end-fire array based on the phase velocity of the surface wave traveling along the dielectric resonator side wall. This phase velocity is estimated from the phase velocity in an infinitely long dielectric rod with the same permittivity and radius as the dielectric resonator antenna. The helical exciter is required to operate in the helix axial mode. The height of the helix is usually taller than the height of the dielectric resonator core. Using this type of excitation, a 3 dB axial-ratio bandwidth of 6.4% was achieved for a sample design with dielectric constant εr ~ 11. The achieved 3 dB axial-ratio bandwidth is greater than that typical of other reported single feed cylindrical dielectric resonator antennas. A prototype of the sample design is fabricated and measured and a good agreement between simulation and measurement is observed. Furthermore, two approaches for the enhancement of the 3 dB axial ratio bandwidth are proposed: removing the central portion of the cylindrical dielectric resonator and using stacked cylinders. The advantages and limitations of each approach are discussed. Another perspective on the proposed design is to consider the antenna as a helix with a dielectric resonator core. In this perspective, the effects of the dielectric core on the helix antenna are discussed.

The second part of the thesis is concerned with the design of thin wideband electromagnetic planar absorber for X- and KKu-band which also has a polarization sensitive transparent window at frequencies lower than L-band. The design is based on a two layer capacitive circuit absorber with the backmetal layer replaced with a polarization sensitive frequency selective surface. The structure is studied for normally incident waves with two orthogonal linear polarizations. The structure is optimized to have high transparency at low frequencies for one of the polarizations and at the same time good absorption efficiency for both polarizations at the high-frequency band. For one of the polarizations a -1.9 dB transmission with a transmission loss of less than 10% at 1 GHz as well as a 2.25:1 (75%) bandwidth of -20 dB reflection reduction are achieved. For the other polarization we obtained more than 3:1 (100%) bandwidth of -19 dB absorption. Compared with our earlier design based on a Jaumann absorber, we succeed in significantly reducing the transmission loss at the transparent window. Furthermore, the module of absorption quality is extensively improved. The improvements are based on using periodic arrangements of resistive patches in the structure design. The investigation of the structure for oblique angles of incidence and non-ideal materials is also accomplished.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , ix, 71 p.
Series
Trita-EE, ISSN 1653-5146
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-101477ISBN: 978-91-7501-481-4 (print)OAI: oai:DiVA.org:kth-101477DiVA: diva2:547965
Public defence
2012-10-05, F3, Lindstedtsvägen 26, KTH, Stockholm, 13:15 (English)
Opponent
Supervisors
Note

QC 20120925

Available from: 2012-09-25 Created: 2012-08-29 Last updated: 2012-09-25Bibliographically approved
List of papers
1. A Circularly Polarized Cylindrical Dielectric Resonator Antenna Using a Helical Exciter
Open this publication in new window or tab >>A Circularly Polarized Cylindrical Dielectric Resonator Antenna Using a Helical Exciter
2012 (English)Report (Other academic)
Abstract [en]

A novel circularly polarized cylindrical dielectric resonator antennaexcited by an external tape helix is presented. The helix is fed by a coaxialline through a small hole on a finite size ground plane. The configurationoffers a compact and easy to fabricate feeding network providing a 3 dBaxial-ratio bandwidth of 6.4%. A prototype of the proposed configurationis fabricated and measured. Measured and simulated return loss, axial-ratio and radiation pattern are presented and discussed together withdesign guidelines.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2012. 14 p.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-96809 (URN)
Note
QC 20120615Available from: 2012-06-15 Created: 2012-06-12 Last updated: 2012-09-25Bibliographically approved
2. A Helix Excited Circularly Polarized Hollow Cylindrical Dielectric Resonator Antenna
Open this publication in new window or tab >>A Helix Excited Circularly Polarized Hollow Cylindrical Dielectric Resonator Antenna
2013 (English)In: IEEE Antennas and Wireless Propagation Letters, ISSN 1536-1225, E-ISSN 1548-5757, Vol. 12, 535-538 p.Article in journal (Refereed) Published
Abstract [en]

In this letter, we use a helix to excite two orthogonal HE11 delta modes in phase quadrature in a hollow cylindrical dielectric resonator antenna to generate circular polarization. As compared to our previous work, it is shown that replacing the cylindrical dielectric resonator antenna with a hollow cylindrical-shaped one leads to a significant enhancement in the 3-dB axial-ratio bandwidth. A design guideline is provided, and three design cases are presented. A prototype for one of the designs is fabricated and measured. Measured and simulated data are presented and discussed. It is shown that the 3-dB axial-ratio bandwidth increases as the wall thickness of the hollow cylindrical dielectric resonator decreases. Furthermore, a reduction in the wall thickness requires a longer helix exciter for similar performance.

Keyword
Circular polarization, dielectric resonator antenna (DRA), helix, hollow cylindrical, probe feed, ring
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-102781 (URN)10.1109/LAWP.2013.2257942 (DOI)000318513900003 ()2-s2.0-84877734983 (Scopus ID)
Note

QC 20130614. Updated from In press to published.

Available from: 2012-09-25 Created: 2012-09-25 Last updated: 2017-12-07Bibliographically approved
3. Bandwidth Enhancementof Helix Excited Cylindrical Dielectric Resonator Antennas by Means of Stacking
Open this publication in new window or tab >>Bandwidth Enhancementof Helix Excited Cylindrical Dielectric Resonator Antennas by Means of Stacking
2012 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Stacking method is used to enhance the 3 dB axial ratio and impedance bandwidth of the circularly polarized cylindrical dielectric resonator antennas excited by an external tape helix. In this method, a dielectric cylinder with lower permittivity than the basement cylindrical dielectric resonator is placed concentrically on top of the basement cylinder. The new configuration offers an axial ratio bandwidth up to 11% and impedance bandwidth of 31%.

Keyword
circular polarization, cylindrical, Dielectric resonator antenna, helix, stack
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-102783 (URN)10.1109/LAPC.2012.6403042 (DOI)000324586800111 ()2-s2.0-84873471868 (Scopus ID)978-146732219-5 (ISBN)
Conference
2012 Loughborough Antennas and Propagation Conference, LAPC 2012, 12 November 2012 through 13 November 2012, Loughborough
Note

QC 20140127

Available from: 2012-09-25 Created: 2012-09-25 Last updated: 2014-01-28Bibliographically approved
4. A comparison of a finite and an infinite antenna array with cylindrical dielectric resonator elements
Open this publication in new window or tab >>A comparison of a finite and an infinite antenna array with cylindrical dielectric resonator elements
2011 (English)In: 2011 30th URSI General Assembly and Scientific Symposium, URSIGASS 2011, 2011Conference paper, Published paper (Refereed)
Abstract [en]

In this paper we compare radiation patterns and mutual coupling in finite and infinite square lattice arrays of dielectric resonator antenna (DRA) elements. The array elements are cavity backed, slot fed cylindrical DRAs that utilizes the HE11δ mode. It is observed that the degree of the mutual coupling for non-edge elements is very close to the mutual coupling between the corresponding elements in the infinite array. However, a large difference is observed in the mutual coupling between the center element and the two corner elements in the finite array with respect to the corresponding elements in the infinite array. The coupling is strongest in the E-plane and it is shown how it changes the embedded element patterns in the array.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-83169 (URN)10.1109/URSIGASS.2011.6050307 (DOI)2-s2.0-81255179657 (Scopus ID)978-142445117-3 (ISBN)
Conference
2011 30th URSI General Assembly and Scientific Symposium, URSIGASS 2011; Istanbul; 13 August 2011 through 20 August 2011
Note
QC 20120229Available from: 2012-02-12 Created: 2012-02-12 Last updated: 2012-09-25Bibliographically approved
5. Partially Transparent Jaumann-Like Absorber Applied to a Curved Structure
Open this publication in new window or tab >>Partially Transparent Jaumann-Like Absorber Applied to a Curved Structure
2011 (English)In: International Journal of Antennas and Propagation, ISSN 1687-5869, E-ISSN 1687-5877, 708987- p.Article in journal (Refereed) Published
Abstract [en]

A Jaumann absorber with its metal backing replaced with a combined low-pass and polarizer FSS is investigated with respect to its absorption and its polarization-dependent low-frequency transparency properties. This structure is applied to an idealized curved wing-front end, and its monostatic radar cross-section is determined. The FSS-Jaumann structure preserves an absorption similar to the planar Jaumann absorber in the higher frequency interval and enables a partial transparency in the TE(z) polarization at 1 GHz. In addition, once the structure is applied to the wing-front end, a significant reduction in two-dimensional radar cross-section for both the TM(z) and TE(z) polarization over 2-16 GHz is observed. A sensitivity analysis shows that the resistivity of the inner resistive layer has a large impact on the 1 GHz transmission.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-51449 (URN)10.1155/2011/708987 (DOI)000296841100001 ()2-s2.0-81555225224 (Scopus ID)
Note
QC 20111213Available from: 2011-12-13 Created: 2011-12-12 Last updated: 2017-12-08Bibliographically approved
6. Design of a wideband rasorber with a polarisation-sensitive transparent window
Open this publication in new window or tab >>Design of a wideband rasorber with a polarisation-sensitive transparent window
2012 (English)In: IET Microwaves, Antennas and Propagation, ISSN 1751-8725, Vol. 6, no 7, 747-755 p.Article in journal (Refereed) Published
Abstract [en]

In this study, the authors present a thin wideband electromagnetic planar absorber for X-and Ku-band, which also has a polarisation-sensitive transparent window at frequencies lower than L-band. The design is based on a two-layer capacitive circuit absorber with the back-metal layer replaced with a polarisation-sensitive frequency-selective surface. The structure is studied for normal incident waves with two orthogonal linear polarisations. The authors optimised the structure to gain high transparency at low frequencies for one of the polarisations and at the same time good absorption efficiency for both polarisations at the high-frequency band. For one of the polarisation a -1.9 dB transmission with the transmission loss of less than 10% at 1 GHz as well as a 2.25:1 (75%) bandwidth of -20 dB reflection reduction are achieved. For the other polarisation, the authors obtained more than 3:1 (100%) bandwidth of -19 dB absorption. The transmission loss is significantly reduced compared to the authors' earlier design based on Jaumann absorber. Furthermore, the module of absorption quality is extensively improved. The improvements are based on using periodic arrangements of resistive patches in the structure design. The investigation of the structure for oblique angles of incidence and non-ideal materials shows that the design is robust.

Place, publisher, year, edition, pages
Institution of Engineering and Technology, 2012
Keyword
Frequency-Selective Surfaces, Radar Absorbers, Dipoles, Jaumann
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-99431 (URN)10.1049/iet-map.2011.0444 (DOI)000305888700005 ()2-s2.0-84862983130 (Scopus ID)
Note

QC 20120730

Available from: 2012-07-30 Created: 2012-07-30 Last updated: 2016-04-26Bibliographically approved

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Citation style
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Output format
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