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• 1.
Sorbonne Univ, L2E, UR2, F-75005 Paris, France..
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Sorbonne Univ, L2E, UR2, F-75005 Paris, France..
Bloch Analysis of Artificial Lines and Surfaces Exhibiting Glide Symmetry2019In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 67, no 7, p. 2618-2628Article in journal (Refereed)

Glide-symmetric structures have recently emerged as a smart choice to design planar lenses and electromagnetic bandgap materials. We discuss here the conditions under which a glide-symmetric structure is equivalent to a nonglide-symmetric structure with a reduced period. To this aim, we propose an analysis method based on network theory to efficiently derive the dispersive behavior of these periodic structures. Both phase and attenuation constants can be determined, with potential applications to both guiding and radiating structures. Retaining higher order modal interactions among cells helps to derive the dispersive behavior of periodic structures more accurately. Furthermore, we take advantage of the higher symmetry of these structures to decrease the computational cost by considering only one half or one-quarter of a unit cell instead of the entire cell. We study one and 2-D glide-symmetric structures and confirm the validity of our analysis with comparisons from commercial software.

• 2.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Additive Manufactured Three Dimensional Luneburg Lens for Satellite Communications2019In: 13th European Conference on Antennas and Propagation, EuCAP 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, article id 8739803Conference paper (Refereed)

A method for designing gradient refractive index (GRIN) lenses with additive manufacturing or 3D-printing at K-u band is presented. To demonstrate the potential of the method, we designed a Luneburg lens using a single low-loss dielectric material available for 3D-printers. The gradient index is realized by varying the local material fill density of the lens. We demonstrate with full wave simulations that the structure is able to transform a spherical electromagnetic wave to a plane wave. When the lens is fed with a rectangular waveguide, the overall antenna has a gain of 23 dBi with side lobe levels of -12.5 dB in K-u band. This lens, when integrated with a circular polarized feeding system, could find application for ground satellite communications.

• 3.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Wireless Sensor Network Utilizing Radio-Frequency Energy Harvesting for Smart Building Applications2018In: IEEE Antennas & Propagation Magazine, ISSN 1045-9243, E-ISSN 1558-4143, Vol. 60, no 5, p. 124-136Article in journal (Refereed)

The scope of this article is to develop a modular radio-frequency (RF) energy-harvesting system for smart buildings that can act as a power source for sensing devices. Electromagnetic field-strength measurements at the main campus of the KTH Royal Institute of Technology in Stockholm, Sweden, were carried out to define the strength of the available ambient signals. Mainly two spectra were available for possible RF harvesting, i.e., two cellular bands [GSM1800 and third generation (3G)] and the 2.45-GHz Wi-Fi band. Based on these measurements, a modular approach for the system was adopted. The system is composed from two modules: 1) a Wi-Fi rectenna system composed of eight dual-polarized patch antennas and 16 rectifiers to produce eight differential voltage sources connected in series and 2) a cellular rectenna system composed of eight linear tapered slot antennas and eight rectifiers to produce four differential voltage sources connected in series. We propose an innovative multiple-input, single-output (MISO) wave rectifier that yields an efficient differential output. Both rectenna modules offer full azimuthal coverage and can operate either together or independently.

• 4.
Ericsson AB, Ericsson Res, Gothenburg, Sweden..
Ericsson AB, Ericsson Res, Gothenburg, Sweden.. Ericsson AB, Ericsson Res, Gothenburg, Sweden.. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Implementation of a compact Ka-band parallel plate Luneburg lens based on a hybrid dielectric/metasurface unit cell2019In: 13th European Conference on Antennas and Propagation, EuCAP 2019, IEEE, 2019, article id 8740306Conference paper (Refereed)

The complete implementation and numerical validation of a compact cost-effective multiport parallel plate Luneburg lens antenna operating at 28 GHz is described in this paper. The lens design consists of two parallel plates separated by a gap where each of them contains a metasurface structure based on a new type of combined dielectric/holey unit cell periodically arranged in a glide-symmetric configuration. The required refractive index is achieved by a combination of coarse control by adding a dielectric in the gap, and fine tuning by changing the height of the holes. The simulations of the final prototype including a flare to ensure a smooth wave transition from the parallel plate configuration to air, as well as a coaxial-to-waveguide-to-parallel plate feeding, show a 20% bandwidth for 11.5 dB return loss, and the crosstalk remains below -15 dB for the same frequency band.

• 5.
Ericsson AB, Ericsson Res, Gothenburg, Sweden. attsson, Martin; Quevedo-Teruel, Oscar.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
A Ka-band glide-symmetric planar Luneburg lens with combined electric/metasurface for 5G communications2018In: 2018 INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION (ISAP), Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)

Here, we propose a cost-effective metasurface lens solution based on the use of metallic glide-symmetric unit cell combined with a dielectric sheet. Our solution reduces significantly the manufacturing and assembly complexity of previously investigated Ka-band Luneburg lens implemented in glide symmetry technology. The required refractive index for this unit cell has been studied for the geometrical parameters, and an efficient transition between different media in the parallel plate configuration of the lens is also investigated.

• 6. Camacho, Miguel
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Mimicking glide symmetry dispersion with coupled slot metasurfaces2017In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 111, no 12, article id 121603Article in journal (Refereed)

In this letter, we demonstrate that the dispersion properties associated with glide symmetry can be achieved in systems that only possess reflection symmetry by balancing the influence of two sublattices. We apply this approach to a pair of coupled slots cut into an infinite perfectly conducting plane. Each slot is notched on either edge, with the complete two-slot system having only mirror symmetry. By modifying the relative size of the notches on either side of the slots, we show that a linear dispersion relation with a degeneracy with non-zero group velocity at the Brillouin zone boundary can be achieved. These properties, until now, only found in systems with glide symmetry are numerically and experimentally validated. We also show that these results can be used for the design of ultra-wideband one-dimensional leaky wave antennas in coplanar waveguide technology.

• 7.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Southeast Univ, State Key Lab Millimeter Wave, Nanjing 210096, Jiangsu, Peoples R China..
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Dispersion Analysis of Coaxial Line Loaded with Twist-Symmetric Half-Rings2018In: 2018 IEEE International Workshop on Antenna Technology, iWAT2018 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)

A coaxial line with half-rings connected to its external conductor is proposed in this paper, to investigate the dispersion properties of a twist-symmetric electromagnetic configuration. We demonstrate that the propagating modes in a twist-symmetric structure are more linear than a conventional structure. Additionally, the bandgap at the Brillouin zone boundaries can be manipulated by tuning the relative angular orientation or translation of the rings. This tuning is equivalent to changing the order of the twist symmetry from 4- to 2-fold. Our proposed geometry finds potential application in fully-metallic reconfigurable filters and phase shifters.

• 8.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Southeast Univ, State Key Lab Millimeter Waves, Nanjing 210096, Jiangsu, Peoples R China.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Sorbonne Univ, Lab Elect & Electromagnetisme, F-75005 Paris, France.. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Modeling and Dispersion Analysis of Coaxial Lines With Higher Symmetries2018In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, no 10, p. 4338-4345Article in journal (Refereed)

In this paper, 1-D periodic structures possessing higher symmetries are proposed and investigated in terms of their dispersion properties. The proposed structures are coaxial lines with coaxial rings periodically loaded on their inner or outer conductors. The higher symmetries, namely, glide and twist symmetries, are obtained by performing an additional geometrical operation within the unit cell of the periodic structure. We demonstrate that the propagating modes exhibit a lower frequency dispersion in higher symmetric coaxial lines. Moreover, the conventional stopbands of periodic structures at their Brillouin zone boundaries can be controlled by breaking the higher symmetry or changing the order of the twist symmetry. A circuit-based analytical method is proposed to calculate the dispersion diagram of the glide-symmetric coaxial lines. The results are validated with a full-wave simulation. Moreover, several prototypes of the twist-symmetric coaxial lines are manufactured and measured. A remarkable agreement is achieved between the measurements and simulations, validating the theoretical results. The proposed structures find potential applications in leaky-wave antennas and fully metallic reconfigurable filters and phase shifters.

• 9.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Dispersion analysis of polar glide symmetry with coaxial rings2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)

In this article, the dispersion properties of a coaxial transmission line with polar glide-symmetric rings are analyzed. This symmetry is obtained by introducing periodic polar rings on either the inner or outer conductor of a coaxial guide. By modifying the relative radii of both rings, we demonstrate that a zero bandgap with non-zero group velocity at the Brillouin zone boundary can be achieved. Such quasi-linear dispersion is analyzed by applying both a circuit-based method and full-wave simulations. A good agreement is achieved between the methods.

• 10. Chen, Z. -L
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Artificial maxwell fisheye lens design and synthesis with using metasurface structure2015In: 2015 International Workshop on Electromagnetics: Applications and Student Innovation Competition, iWEM 2015, Institute of Electrical and Electronics Engineers Inc. , 2015Conference paper (Refereed)

In this paper, we use a periodic structure to produce a Maxwell's fisheye lens and investigate some important information such as power, efficiency, etc. At Chapter 1, we describe some introduction about the surface plasmon polariton (SPP), frequency selective surface (FSS), concentration power by using lens. At Chapter 2, we describe some theorem about we need to use like Transmission line modal, high impedance surface, periodic structure lens. At Chapter 3, we describe our design and we show some simulation results about the surface wave Maxwell's fisheye lens. At chapter 4, we discuss our results about the fisheye lens. At chapter 5, we will draw the conclusions. © 2015 IEEE.

• 11.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Reducing the Dispersion of Periodic Structures with Twist and Polar Glide Symmetries2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 10136Article in journal (Refereed)

In this article, a number of guiding structures are proposed which take advantage of higher symmetries to vastly reduce the dispersion. These higher symmetries are obtained by executing additional geometrical operations to introduce more than one period into the unit cell of a periodic structure. The specific symmetry operations employed here are a combination of p-fold twist and polar glide. Our dispersion analysis shows that a mode in a structure possessing higher symmetries is less dispersive than in a conventional structure. It is also demonstrated that, similar to the previously studied Cartesian glide-symmetric structures, polar glide-symmetric structures also exhibit a frequency independent response. Promising applications of these structures are leaky-wave antennas which utilize the low frequency dependence.

• 12.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Sorbonne Univ, Lab Electron & Electromagnetisme, F-75005 Paris, France.. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Propagation characteristics of periodic structures possessing twist and polar glide symmetries2019In: EPJ Applied Metamaterials, ISSN 2272-2394, Vol. 6, article id 14Article in journal (Refereed)

In this article, we provide an overview of the current state of the research in the area of twist symmetry. This symmetry is obtained by introducing multiple periods into the unit cell of a periodic structure through a rotation of consecutive periodic deformations around a symmetry axis. Attractive properties such as significantly reduced frequency dispersion and increased optical density, compared to purely periodic structures, are observed. The direct link between the symmetry order and these properties is illustrated through numerical simulations. Moreover, polar glide symmetry is introduced, and is shown to provide even further control of the dispersion properties of periodic structures, especially when combined with twist symmetry. Twist symmetries can, with benefit, be employed in the development of devices for future communication networks and space applications, where fully metallic structures with accurate control of the dispersion properties are desired.

• 13.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
Fully-metallic, Low-dispersive, Leaky-wave Fed Lens Antenna for 60 GHz Base Station Applications2018In: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena, METAMATERIALS 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 90-92Conference paper (Refereed)

The guiding structure commonly employed in leaky-wave antennas is dispersive, resulting in beam-steering with frequency. This behavior reduces operational bandwidth in point-to-point communication applications. In this work, we present an approach that aims at increasing the operational bandwidth of leaky-wave antennas by the employment of a metasur-face lens.

• 14.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Ericsson AB, Syst & Technol, S-16480 Stockholm, Sweden.. Hamburg Univ Technol, Inst Theoret Elektrotech, D-21079 Hamburg, Germany.. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Low-Dispersive Glide-Symmetric Leaky-Wave Antenna at 60 GHz2019In: 13th European Conference on Antennas and Propagation, EuCAP 2019, IEEE, 2019, article id 8740212Conference paper (Refereed)

In this work we demonstrate a method for producing low-loss, non-squinting, directive leaky-wave antennas (LWAs) for millimeter-wave frequencies. The scanning behaviour of the radiation pattern arises from the dispersive nature of the waveguide mode, which is leaking out when opening the wave guiding structure. We propose a method to cancel the dispersive behaviour, by allowing the leaked waves to refract in a dispersive prism-lens. The proposed method allows for fully metallic implementation of the antenna, resulting in low losses. Furthermore, high directivity is easily achieved with a simple feeding. The corresponding theory is outlined, and the proposed method is used to design an antenna operating at 60 GHz. The obtained bandwidth, with less than 1 degrees beam scanning, is 20% in simulations and the realized gain of the antenna is 17 dB across the entire bandwidth. The design is proposed as an alternative to obtain high gain antennas for 5G applications, in which low losses and narrow beams are expected to be key features for mm-waves.

• 15. Dahlberg, Oskar
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Accurate and low-dispersive control of refractive properties in fully metallic waveguides possessing twist symmetry2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)

We here present a method of reducing the dispersive nature of periodic structures by utilizing twist symmetries. A dispersion study of four different 1D periodic structures is conducted to present the advantage of structures possessing twist symmetries. The analysis shows a clearly reduced frequency dependence of twist-symmetric structures, compared to more simple periodic structures. Additional advantage provided by twist symmetries is the accurate control of the refractive properties of the structures. Promising applications of twist-symmetric guiding structures are leaky-wave antennas, filters and phase shifters.

• 16.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Sorbonne Univ, Lab Elect & Electromagnetisme, F-75005 Paris, France.. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Fully Metallic Flat Lens Based on Locally Twist-Symmetric Array of Complementary Split-Ring Resonators2019In: Symmetry, ISSN 2073-8994, E-ISSN 2073-8994, Vol. 11, no 4, article id 581Article in journal (Refereed)

In this article, we demonstrate how twist symmetries can be employed in the design of flat lenses. A lens design is proposed, consisting of 13 perforated metallic sheets separated by an air gap. The perforation in the metal is a two-dimensional array of complementary split-ring resonators. In this specific design, the twist symmetry is local, as it is only applied to the unit cell of the array. Moreover, the twist symmetry is an approximation, as it is only applied to part of the unit cell. First, we demonstrate that, by varying the order of twist symmetry, the phase delay experienced by a wave propagating through the array can be accurately controlled. Secondly, a lens is designed by tailoring the unit cells throughout the aperture of the lens in order to obtain the desired phase delay. Simulation and measurement results demonstrate that the lens successfully transforms a spherical wave emanating from the focal point into a plane wave at the opposite side of the lens. The demonstrated concepts find application in future wireless communication networks where fully-metallic directive antennas are desired.

• 17. Diallo, C. D.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Parallel-plate-waveguide luneburg lens through a holey plate metasurface2015In: 2015 9th European Conference on Antennas and Propagation, EuCAP 2015, IEEE , 2015Conference paper (Refereed)

This paper presents a parallel plate waveguide (PPW) Luneburg lens designed using an array of subwavelength circular holes etched on a metallic plate printed on a dielectric substrate. Variation of the hole radius modulates the effective permittivity. The lens operates in the Ka band of frequencies in a quasi-TEM mode. Easy to implement and low cost, the lens could be a good candidate as a lens-like beamformer for low loss multiple beam applications.

• 18.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Ericsson AB, Ericsson Res, S-41756 Gothenburg, Sweden.. Ericsson AB, Ericsson Res, S-41756 Gothenburg, Sweden.. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Using Glide-Symmetric Holes to Reduce Leakage Between Waveguide Flanges2018In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 28, no 6, p. 473-475Article in journal (Refereed)

In this letter, a novel cost-effective flange is proposed to prevent the leakage created by undesired air gaps between flanges of two mating waveguides. The cause of an undesired gap can be surface curvature, dirt, human mistakes, or misalignment. Our proposal consists of machining glide-symmetric holes around the waveguide aperture on the flanges. Due to the glide symmetry properties, an identical pattern of the holes is possible at both sides, thus becoming glide-symmetric when they are mated together.

• 19.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Lens antennas using QCTO technique2015In: 2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), USNC-URSI 2015 - Proceedings, IEEE , 2015, p. 168-Conference paper (Refereed)

Quasi Conformal Transformation Optics (QCTO) is employed here to produce 3D gradient-index lenses. These lenses are able to improve radiation properties of conventional antennas, such as gain, side lobe levels and cross polarization.

• 20.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
A bespoke lens for a slot log-spiral excitation2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)

In this paper, a bespoke lens has been designed for a slot log-spiral excitation. The performance of this lens is compared with a conventional hyper-hemispherical lens. Using the bespoke lens methodology, the specific electromagnetic properties of the slot log-spiral excitation are obtained and its phase fronts are transformed to flat phase fronts by a QCTO (quasi-conformal transformation optics) technique. The performance of the lenses is evaluated with the radiation properties. The bespoke lens produces an improvement in terms of directivity and side lobe levels.

• 21.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Bespoke Lenses Based on Quasi-Conformal Transformation Optics Technique2017In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 65, no 5, p. 2256-2264Article in journal (Refereed)

In this paper, a systematic method to design a quasioptimum lens profile based on quasi-conformal transformation optics technique for a given excitation is presented. This method is applied to a number of conventional antennas, such as an aperture and a log-spiral slot. In all these configurations, an increase of the directivity is observed. Furthermore, using this method, a quasi-optimum graded index lens for a broadband enhanced leaky slot excitation is designed and the results are compared with a hyperhemispherical lens with and without matching layers. Our proposed methodology demonstrates to be able to increase the directivity, to reduce the sidelobes and the cross polarization in a broad bandwidth from 20 to 70 GHz. Due to the continuously changed dielectric constant of the lens profile, reflections are also reduced considerably inside the lens.

• 22.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Contact-less Measurement by Using Glide-symmetric Holes on Flanges2018In: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena, METAMATERIALS 2018, Institute of Electrical and Electronics Engineers Inc. , 2018, p. 105-107Conference paper (Refereed)

We present a cost-effective solution for contact-less measurement of waveguiding structures at high frequencies. Drilling glide-symmetric holey EBG (electromagnetic band gap) on the flanges, the leakage caused by undesired air-gaps, by the result of human mistakes or instrumental errors, between the flanges can be minimized considerably and contact-less measurement becomes possible.

• 23.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
Contact-less Measurement by Using Glide-symmetric Holes on Flanges2018In: 2018 12TH INTERNATIONAL CONGRESS ON ARTIFICIAL MATERIALS FOR NOVEL WAVE PHENOMENA (METAMATERIALS), IEEE , 2018, p. 105-107Conference paper (Refereed)

We present a cost-effective solution for contact-less measurement of waveguiding structures at high frequencies. Drilling glide-symmetric holey EBG (electromagnetic band gap) on the flanges, the leakage caused by undesired air-gaps, by the result of human mistakes or instrumental errors, between the flanges can be minimized considerably and contact-less measurement becomes possible.

• 24.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Ultrawideband Anisotropic Glide-Symmetric Metasurfaces2019In: IEEE Antennas and Wireless Propagation Letters, ISSN 1536-1225, E-ISSN 1548-5757, Vol. 18, no 8, p. 1547-1551Article in journal (Refereed)

This letter presents a method to realize anisotropic two-dimensional designs with wideband operation. Glide symmetry has been proven to increase the bandwidth and equivalent refractive index of periodic structures. Here, two anisotropic glide-symmetric unit cells are proposed and characterized. Our simulated results prove that these unit cells follow the general behavior of periodic structures possessing glide symmetry. Moreover, we demonstrate that higher level of anisotropy can also be achieved by glide symmetry. Combining our proposed anisotropic glide-symmetric unit cell and transformation optics, a 30% compressed Luneburg lens is designed. The lens operates from 1 to 13 GHz.

• 25.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
Broadband Planar Leaky Wave Antenna Using Glide-symmetric Meandered Transmission LineManuscript (preprint) (Other (popular science, discussion, etc.))
• 26.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Low-cost metasurface using glide symmetry for integrated waveguides2016In: 2016 10th European Conference on Antennas and Propagation, EuCAP 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, article id 7481261Conference paper (Refereed)

A novel Electromagnetic Band Gap (EBG) structure based on an off-shifted periodic metasurface is presented here. This technique can be employed for packaging of electrical circuits and gap waveguide technology. The proposed structure is easy to manufacture since it only requires drilling holes in metallic plates, reducing the cost when compared to previous works based on other textured surfaces.

• 27.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Ferdowsi Univ Mashhad, Dept Elect Engn, Mashhad, Razavi Khorasan, Iran.. Ferdowsi Univ Mashhad, Dept Elect Engn, Mashhad, Razavi Khorasan, Iran..
Design of Nonmagnetic All-mode Waveguide Coupler with Perfect Transmission Using Transformation Optics2019In: 13th European Conference on Antennas and Propagation, EuCAP 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, article id 8739511Conference paper (Refereed)

Using the transformation optics method together with the basic properties of Maxwell equations, a compact nonmagnetic waveguide coupler is designed that can ideally couple all TMn modes. Two compression functions are proposed to provide a perfect smooth transition between the waveguides. This coupler can be used to guide and compress a vacuumfilled waveguide to a smaller waveguide with a predefined higher dielectric constant inside. The design method is validated by simulated examples using COMSOL Multiphysics.

• 28.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Ferdowsi Univ Mashhad, Dept Elect Engn, Mashhad, Iran.. Ferdowsi Univ Mashhad, Dept Elect Engn, Mashhad, Iran..
Transformation optics for perfect two-dimensional non-magnetic all-mode waveguide couplers2019In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 9, no 3, p. 1320-1332Article in journal (Refereed)

Here, we demonstrate that transformation optics can be used to produce 2-D non-magnetic waveguide couplers with no reflections. Our approach consists of using a scaling function for reflection suppression and introducing an auxiliary function in the transformation optics formulation to achieve a non-magnetic medium for coupling the TM polarization. To demonstrate the potential of this method, two non-magnetic waveguide couplers are designed. The first one satisfies the Brewster angle condition for any arbitrary incidence angle (TMn modes), extending the performance of couplers previously reported in the literature that only operate for TEM (TM0 mode), i.e. waves with normal incidence. Our method can be applied to match any given dielectric constant. Our results demonstrate that for a given mode (angle), we achieve a perfect match to a defined dielectric constant. The second design removes the dependence of the reflectionless condition to the incident angle at the boundary. Hence, this coupler works for all incident angles (TMn modes). It is used to compress all the modes into a region with a higher predefined refractive index.

• 29.
European Space Agcy, Antenna & Sub Millimetre Waves Sect, Noordwijk, Netherlands. iao, Qingbi; Quevedo-Teruel, Oscar.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
The Water Drop Lens: A Modulated Geodesic Lens Antenna Based on Parallel Curves2018In: ISAP 2018 - 2018 International Symposium on Antennas and Propagation, Institute of Electrical and Electronics Engineers (IEEE), 2018, article id 8627878Conference paper (Refereed)

This paper discusses the design of parallel plate waveguide geodesic nses based on parallel curves enabling low-profile beamformers with a ry wide angular scanning range. The proposed approach provides smooth ns profiles with additional degrees of freedom for the optimization of odesic lenses, enabling Gaussian beam but also shaped patterns. The tational symmetry of the lens results in a shape looking like water op ripples, also known as capillary waves, at the surface of a fluid, nce the water drop lens appellation.

• 30.
European Space Agcy, Antenna & Submillimetre Wave Sect, Noordwijk, Netherlands..
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
The Water Drop Lens: a Low-Profile Geodesic Parallel Plate Waveguide Lens Antenna for Space Applications2019In: 13th European Conference on Antennas and Propagation, EuCAP 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, article id 8739805Conference paper (Refereed)

This paper introduces the design of a parallel plate waveguide geodesic lens modulated with spline functions. This geodesic lens design is rotational-symmetric, which naturally provides a high pattern stability over a wide angular range. The proposed design is thoroughly compared to the reference Rinehart-Luneburg lens and numerical results indicate similar electromagnetic performance, including scattering parameters and radiation, while enabling a height reduction by a factor of 2.6. This beamformer provides very wide angular scanning up to +/- 70 degrees with scan losses below 3 dB. The lens can be designed to provide very high aperture efficiency (between 80 and 90%) over a wide frequency operating range. Analyses were performed over the frequency range 26-32 GHz, demonstrating very stable performance. The very smooth shape of the lens is particularly attractive for applications at millimeter and sub-millimeter wavelengths.

• 31.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Dispersion Analysis of 2-D Glide-Symmetric Corrugated Metasurfaces Using Mode-Matching Technique2018In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 28, no 1, p. 1-3Article in journal (Refereed)

In this letter, wave propagation in 2-D doubled corrugated metasurfaces, including glide-symmetric corrugated metasurfaces, embedded in a thin parallel plate waveguide have been analyzed using the mode matching method. The general dispersion equation for propagation at different directions is derived and dispersion surfaces have been obtained for three different cases. The results are in good agreement with reference results obtained using CST Microwave Studio. Moreover, the method is accurate and computationally much faster than CST Microwave Studio and similar commercial software.

• 32.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Twist and Polar Glide Symmetries: an Additional Degree of Freedom to Control the Propagation Characteristics of Periodic Structures2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8Article in journal (Refereed)

New high-frequency 5G and satellite communication systems require fully-metallic antennas and electromagnetic components. These components can be implemented with truncated versions of periodic structures. In order to achieve the desired performance of these future devices, it is of crucial importance to have a precise control of the propagation properties, i.e. the frequency dispersion behavior and stop-bands. Here, we demonstrate the potential use of higher symmetries to diminish the frequency dispersion of periodic structures and control the width of stop-bands with a new type of fully-metallic transmission line, which is loaded with holes on a twist-symmetric configuration. Simulated and experimental results confirm the intrinsic link between the propagation characteristics and the symmetries of a periodic structure. Additionally, we provide a definitive explanation of the recently discovered polar glide symmetry and its potential combination with twist symmetries to produce low-dispersive materials and reconfigurable stop-bands. The promising properties of these structures are demonstrated with a fully-metallic reconfigurable filter, which could be used for future high-frequency 5G and satellite communication systems.

• 33.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Mimicking Twist Symmetry Properties in Flat Structures2019In: 13th European Conference on Antennas andPropagation (EUCAP), Institute of Electrical and Electronics Engineers (IEEE), 2019Conference paper (Refereed)

Twist symmetry provides an additional degree of freedom to control the wave propagation in periodic structures. However, real twist-symmetric structures are cylindrical structures that have a high cost of manufacturing. In addition, they are not compatible with the available, low-cost and flat technologies, such as microstrip technology. Here, we investigate the possibility of mimicking the dispersion properties of twist symmetry in flat structures.

• 34.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Analysis of wave propagation in plasmonic holey metasurfaces with cylindrical holes2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)

The wave propagation along a plasmonic holey metasurface when a metallic plate is located in its proximity has been analyzed using a mode matching technique. With this analysis, we demonstrate that decreasing the distance between the metallic plate and the holey surface excites nonresonant higher order modes in the structure. Therefore, considering only the dominant mode inside the holes, as the previous simpler models assumed, is not sufficient to analyze this type of metasurfaces.

• 35. Horsley, S. A. R.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Removing singular refractive indices with sculpted surfaces2014In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, p. 4876-Article in journal (Refereed)

The advent of Transformation Optics established the link between geometry and material properties, and has resulted in a degree of control over electromagnetic fields that was previously impossible. For waves confined to a surface it is known that there is a simpler, but related, geometrical equivalence between the surface shape and the refractive index, and here we demonstrate that conventional devices possessing a singularity-that is, the requirement of an infinite refractive index-can be realised for waves confined to an appropriately sculpted surface. In particular, we redesign three singular omnidirectional devices: the Eaton lens, the generalized Maxwell Fish-Eye, and the invisible sphere. Our designs perfectly reproduce the behaviour of these singular devices, and can be achieved with simple isotropic media of low refractive index contrast.

• 36. Hsieh, K. -H
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
The manipulation of surface plasmon polaritons and design of luneburg lens based on periodic patch arrays2015In: 2015 International Workshop on Electromagnetics: Applications and Student Innovation Competition, iWEM 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 1-2Conference paper (Refereed)

We present a surface constitutes arrays of periodic patches, which may serve as the metasurface to synthesize the Luneburg lens. The main purpose is by using different sizes of patches to achieve different refractive index at each stage, and get the proper function of Luneburg lens.

• 37.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Antenna and Sub-Millimeter Waves Section, European Space Agency, Noordwijk, 2200 AG, Netherlands. KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Compact Multibeam Fully Metallic Geodesic Luneburg Lens Antenna Based on Non-Euclidean Transformation Optics2018In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 66, no 12, p. 7383-7388Article in journal (Refereed)

Non-Euclidean transformations have been recently proposed to produce a link between 3-D homogeneous surfaces and 2-D dielectric lenses. Therefore, the propagation in a geometrical surface has the same response of an equivalent refractive index distribution. By using this concept, we propose here a fully metallic Luneburg lens where the propagation is only in the air. Two metallic plates, following a curved shape, are employed to support the propagation mimicking the designed curvature. To reduce the height of the required curvature, the surface has been mirrored twice with respect to two z constant planes. The lens is fed by 11 waveguide ports spaced with an angle of 12.5° providing 1-D beam scanning over an angular range of ±62.5°. A prototype is manufactured and measured with a good agreement with the simulated results between 25 and 36 GHz to demonstrate the concept.

• 38.
KTH, School of Electrical Engineering and Computer Science (EECS).
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Higher mode propagation in periodic patch structures with two-dimensional glide symmetries2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)

A periodic structure possesses glide symmetry if it is composed of two lattices mirrored and translated half period. We propose here a new king of two-dimensional glide-symmetric structure in microstrip technology. The effect of the glide symmetry on the higher modes is studied in this paper. We compare a glide-symmetric case with only mirrored metasurfaces, and a quarter-period translation case.

• 39.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
Univ Carlos III Madrid, Dept Commun & Signal Theory, Leganes 28911, Spain.. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
Ka-Band Fully Metallic TE40 Slot Array Antenna With Glide-Symmetric Gap Waveguide Technology2019In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 67, no 10, p. 6410-6418Article in journal (Refereed)

Gap waveguide has recently been proposed as a low-loss and low-cost technology for millimeter-wave components. The main advantage of the gap waveguide technology is that the microwave components can be manufactured in two metallic pieces that are assembled together without electrical contact. The leakage through a thin air gap between the two pieces is prevented by a 2-D periodic structure offering an electromagnetic bandgap (EBG). This EBG is conventionally implemented with metallic pins. Here, we propose the usage of a holey glide-symmetric EBG structure to design a $4\times 4$ slot array antenna that is fed with a TE40 mode. The TE40 excitation is designed based on a TE10-TE20 mode converter whose performance is initially evaluated by radiation pattern measurements. The final antenna, the $4\times 4$ slot array antenna, was manufactured in aluminum by computer numerical control (CNC) milling. The antenna has a rotationally symmetric radiation pattern that could find application as a reference antenna as well as for 5G point-to-point communications.

• 40. Manholm, L.
KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
A two-dimensional all metal Luneburg lens using glide-symmetric holey metasurface2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)

A two-dimensional Luneburg lens multiport antenna at 28GHz is presented, where an all metal metasurface structure is used to control the effective refractive index. The metasurface lens has glide-symmetric pin-loaded holes in the two plates of the parallel plate waveguide lens. This glide-symmetric configuration enhances the bandwidth of operation for the same equivalent refractive index. Excellent port matching and radiation performance are demonstrated through simulations of the complete antenna that is fed with 11 waveguides.

• 41.
Imperial Coll London, Dept Phys, Blackett Lab, Prince Consort Rd, London SW7 2AZ, England..
Imperial Coll London, Dept Phys, Blackett Lab, Prince Consort Rd, London SW7 2AZ, England.. Univ Sannio, Dept Engn, Fields & Waves Lab, I-82100 Benevento, Italy.. Nanjing Univ, Sch Phys, Natl Lab Solid State Microstruct, Nanjing 210093, Jiangsu, Peoples R China.;Nanjing Univ, Collaborat Innovat Ctr Adv Microstruct, Nanjing 210093, Jiangsu, Peoples R China.. Univ Exeter, Dept Phys & Astron, Stocker Rd, Exeter EX4 4QL, Devon, England.. Univ Birmingham, Sch Phys & Astron, Birmingham B15 2TT, W Midlands, England.. Univ Birmingham, Sch Phys & Astron, Birmingham B15 2TT, W Midlands, England.. Univ Exeter, Dept Phys & Astron, Stocker Rd, Exeter EX4 4QL, Devon, England.. KTH. Chalmers Univ, Dept Phys, SE-41296 Gothenburg, Sweden.. Vrije Univ Brussel, Pl Laan 2, B-1050 Brussels, Belgium.. Univ Siena, Dipartimento Ingn Informaz & Sci Matemat, Via Roma 56, I-53100 Siena, Italy.. Univ Siena, Dipartimento Ingn Informaz & Sci Matemat, Via Roma 56, I-53100 Siena, Italy.. Univ Siena, Dipartimento Ingn Informaz & Sci Matemat, Via Roma 56, I-53100 Siena, Italy.. KTH. Queen Mary Univ London, Sch Elect Engn & Comp Sci, London E1 4FZ, England.. Univ Lancaster, Phys Dept, Lancaster LA1 4YB, England.. Univ Lancaster, Phys Dept, Lancaster LA1 4YB, England.;Sci Tech Daresbury, Cockcroft Inst, Daresbury WA4 4AD, England.. Oak Ridge Natl Lab, Computat Sci & Engn Div, Quantum Informat Sci Grp, Oak Ridge, TN 37831 USA.. Purdue Univ, Birck Nanotechnol Ctr, Sch Elect & Comp Engn, W Lafayette, IN 47907 USA.;Purdue Univ, Purdue Quantum Ctr, W Lafayette, IN 47907 USA.. Weizmann Inst Sci, Phys Complex Syst, IL-7610001 Rehovot, Israel.. Univ Maryland, Inst Syst Res, College Pk, MD 20742 USA.. Towson Univ, Dept Phys Astron & Geosci, Towson, MD 21252 USA.. Karlsruhe Inst Technol, Inst Angew Phys, Wolfgang Gaede Str 1, D-76131 Karlsruhe, Germany.. Karlsruhe Inst Technol, Inst Angew Phys, Wolfgang Gaede Str 1, D-76131 Karlsruhe, Germany.. Karlsruhe Inst Technol, Inst Angew Phys, Wolfgang Gaede Str 1, D-76131 Karlsruhe, Germany.. Duke Univ, Elect & Comp Engn, POB 90291, Durham, NC 27708 USA..
Roadmap on transformation optics2018In: Journal of Optics, ISSN 2040-8978, E-ISSN 2040-8986, Vol. 20, no 6, article id 063001Article in journal (Refereed)

Transformation optics asks, using Maxwell's equations, what kind of electromagnetic medium recreates some smooth deformation of space? The guiding principle is Einstein's principle of covariance: that any physical theory must take the same form in any coordinate system. This requirement fixes very precisely the required electromagnetic medium. The impact of this insight cannot be overestimated. Many practitioners were used to thinking that only a few analytic solutions to Maxwell's equations existed, such as the monochromatic plane wave in a homogeneous, isotropic medium. At a stroke, transformation optics increases that landscape from 'few' to 'infinity', and to each of the infinitude of analytic solutions dreamt up by the researcher, there corresponds an electromagnetic medium capable of reproducing that solution precisely. The most striking example is the electromagnetic cloak, thought to be an unreachable dream of science fiction writers, but realised in the laboratory a few months after the papers proposing the possibility were published. But the practical challenges are considerable, requiring meta-media that are at once electrically and magnetically inhomogeneous and anisotropic. How far have we come since the first demonstrations over a decade ago? And what does the future hold? If the wizardry of perfect macroscopic optical invisibility still eludes us in practice, then what compromises still enable us to create interesting, useful, devices? While three-dimensional (3D) cloaking remains a significant technical challenge, much progress has been made in two dimensions. Carpet cloaking, wherein an object is hidden under a surface that appears optically flat, relaxes the constraints of extreme electromagnetic parameters. Surface wave cloaking guides sub-wavelength surface waves, making uneven surfaces appear flat. Two dimensions is also the setting in which conformal and complex coordinate transformations are realisable, and the possibilities in this restricted domain do not appear to have been exhausted yet. Beyond cloaking, the enhanced electromagnetic landscape provided by transformation optics has shown how fully analytic solutions can be found to a number of physical scenarios such as plasmonic systems used in electron energy loss spectroscopy and cathodoluminescence. Are there further fields to be enriched? A new twist to transformation optics was the extension to the spacetime domain. By applying transformations to spacetime, rather than just space, it was shown that events rather than objects could be hidden from view; transformation optics had provided a means of effectively redacting events from history. The hype quickly settled into serious nonlinear optical experiments that demonstrated the soundness of the idea, and it is now possible to consider the practical implications, particularly in optical signal processing, of having an 'interrupt-without-interrupt' facility that the so-called temporal cloak provides. Inevitable issues of dispersion in actual systems have only begun to be addressed. Now that time is included in the programme of transformation optics, it is natural to ask what role ideas from general relativity can play in shaping the future of transformation optics. Indeed, one of the earliest papers on transformation optics was provocatively titled 'General Relativity in Electrical Engineering'. The answer that curvature does not enter directly into transformation optics merely encourages us to speculate on the role of transformation optics in defining laboratory analogues. Quite why Maxwell's theory defines a 'perfect' transformation theory, while other areas of physics such as acoustics are not apparently quite so amenable, is a deep question whose precise, mathematical answer will help inform us of the extent to which similar ideas can be extended to other fields. The contributors to this Roadmap, who are all renowned practitioners or inventors of transformation optics, will give their perspectives into the field's status and future development.

• 42. Mitchell-Thomas, R. C.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Altering antenna radiation properties with transformation optics2015In: 2015 9th European Conference on Antennas and Propagation, EuCAP 2015, IEEE conference proceedings, 2015Conference paper (Refereed)

In this paper, the technique of quasi-conformal transformation optics is utilized to design lenses that can alter the radiation properties of common antennas. The performance of these lenses is simulated using numerical software and analysis shows that the directivity can be increased significantly, or the radiation patterns can be changed as desired. Therefore, using this technique, bespoke lenses can be designed that create complex radiation from simple antenna feed types, for a number of high-frequency applications.

• 43. Mitchell-Thomas, R. C.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Broadband Metasurface for Surface Wave Lenses2016In: 2016 URSI INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC THEORY (EMTS), IEEE, 2016, p. 605-606Conference paper (Refereed)

This paper presents the design of a metasurface that exhibits glide symmetry. This allows the metasurface to support a mode that is confined to the surface for a broad band of frequencies. In addition it is shown that the mode index of such surfaces depends only weakly on the frequency over a given range. We then propose these structures as a practical solution to the fabrication of broadband surface-wave lenses designed using quasi-conformal transformation optics technique.

• 44. Mitchell-Thomas, R. C.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Lenses on curved surfaces2014In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, no 12, p. 3551-3554Article in journal (Refereed)

This Letter presents a theory that allows graded index lenses to be mapped onto arbitrary rotationally symmetric curved surfaces. Examples of the Luneburg and Maxwell fish-eye lens are given, for numerous surfaces, always resulting in isotropic permittivity requirements. The performance of these lenses is initially illustrated with full-wave simulations utilizing a waveguide structure. A transformation of the refractive index profiles is then performed to design surface-wave lenses, where the dielectric layer is not only isotropic but also homogenous, demonstrating the applicability and ease of fabrication.

• 45. Mitchell-Thomas, R. C.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
The anti-fish eye cloak for surface wave antennas2014In: 8th European Conference on Antennas and Propagation, EuCAP 2014, 2014, p. 267-268Conference paper (Refereed)

In this paper a new lens, named the anti-fish eye lens, is proposed and its relation to the Maxwell fish eye lens is described. This novel lens is then applied to cloak an object positioned underneath it, to electromagnetic waves that are confined to the surface. The performance of the lens in reforming the cylindrical wave fronts is illustrated with numerical simulations. This lens has direct applications for surface wave antennas that are conformal to curved structures to remove the influence of the curvature, the consequence of which would detrimentally affect the directivity because of the distortion of the wavefronts. Therefore, using this technique, the performance of surface wave antennas on curved surfaces can be equivalent to those on flat surfaces.

• 46. Mitchell-Thomas, R. C.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Omnidirectional surface wave cloak using an isotropic homogeneous dielectric coating2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 30984Article in journal (Refereed)

The field of transformation optics owes a lot of its fame to the concept of cloaking. While some experimental progress has been made towards free-space cloaking in three dimensions, the material properties required are inherently extremely difficult to achieve. The approximations that then have to be made to allow fabrication produce unsatisfactory device performance. In contrast, when surface wave systems are the focus, it has been shown that a route distinct from those used to design free-space cloaks can be taken. This results in very simple solutions that take advantage of the ability to incorporate surface curvature. Here, we provide a demonstration in the microwave regime of cloaking a bump in a surface. The distortion of the shape of the surface wave fronts due to the curvature is corrected with a suitable refractive index profile. The surface wave cloak is fabricated from a metallic backed homogeneous dielectric waveguide of varying thickness, and exhibits omnidirectional operation.

• 47. Mitchell-Thomas, Rhiannon C.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2D optical transformations for surfaces2014In: IEEE Antennas and Propagation Society, AP-S International Symposium (Digest), 2014, p. 761-762Conference paper (Refereed)

This paper describes a two-dimensional optical transformation method that can be used to tailor the propagation of waves confined to a surface. Virtual and physical geometries are employed, and the equivalence of the wave behaviour on these two different surfaces is illustrated using full wave simulations of a graded-index loaded waveguide. This technique has great promise to design devices that are fabricated from metasurfaces.

• 48. Osipov, A. V.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
Flattened generalized Maxwell fish-eye lens limiting sub-unity refractive index regions2015In: 2015 9th European Conference on Antennas and Propagation, EuCAP 2015, IEEE conference proceedings, 2015Conference paper (Refereed)

In this paper we propose the designs of three wide- band flattened generalized Maxwell fish-eye lenses. The designs were performed using transformation optics with quasiconformal mapping. This transformation allows not only to arbitrarily shape the lenses preserving the same electromagnetic response, but also to reduce the sub-unity regions which limit the bandwidth of operation. These devices have practical applications as wide-angle scanner and power divider matched in terms of the shape with conventionally planar receiver/transceiver arrays.

KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Glide Symmetry to Prevent the Lowest Stopband of Printed Corrugated Transmission Lines2018In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 28, no 9, p. 750-752, article id 8432475Article in journal (Refereed)

In this letter, we demonstrate that the dispersion properties of printed double-sided parallel-strip lines can be controlled by using glide symmetry. Glide symmetry is introduced in with corrugations in both strips of a double-sided line. We demonstrate that glide symmetry eliminates the stopband between first and second propagating modes and yields to a higher propagation constant, preserving its linearity, and the broadband nature of the underlying guiding technology. Thus, the glide-symmetric double-sided line can be designed to possess a high equivalent refractive index in an ultrawide range of frequencies. These exceptional properties have been numerically and experimentally validated. Finally, we demonstrate the possibilities of this technology with a specific design, a glide-symmetric double-sided parallel-strip line with filtering properties. Potential applications are low-dispersive leaky-wave antennas and electromechanical tunable phase shifters and filters.

KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
Glide-symmetric holey structures with selected bandgaps for gap-waveguide technology2018In: IET Conference Publications, Institution of Engineering and Technology, 2018, Vol. CP741, no CP741Conference paper (Refereed)

Here, we propose a new technique to accurately define and select the bandgap regions in gap waveguide technology based on glide-symmetric holey structures. This selection is accomplished by breaking the symmetry of the periodic structure. The advantage of this proposal is that filtering properties are added intrinsically in the waveguides, reducing the total complexity of the overall device, in which additional filters may not be necessary.

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