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Modeling curved metasurface structures repre-sents a computing challenge due to the complexity of con-sidered designs. This creates a need for specialized effi-cient analysis methods. An approach that combines the spectral-domain field representation and surface sheet impedance concept is proposed. The considered cascaded cylindrical metasurface structures can span across only a part of a canonical surface and unit cell elements can vary along the metasurface, giving a spatially-varying sheet impedance. The analysis method is experimentally verified against a cylindrical metasurface for shaping the feed antenna beam. The problem of manufacturing curved metasurfaces is also discussed in the paper.

Here, we study the propagation of a twist-symmetric dielectric rod with three different methods: eigenmode solver, multimode Bloch analysis, and scattering parameters of a truncated structure. With the eigenmode analysis, we demonstrate that these structures permit the propagation of circularly polarized modes, and only one of the modes has a stopband in the first Brillouin zone. These results are corroborated with the simulation of a truncated structure, demonstrating that the propagation is only possible for one of the modes at a given frequency band. Finally, the multimode Bloch analysis is used to also characterize the attenuation constant in the stopband.

We propose a circular twist-symmetric dielectric waveguide that is polarization-selective. In the practical implementation of optical fibers, a selective circular polarization is more convenient than its linearly polarized counterpart where previous knowledge of the emitted polarization from the transmitter is unknown. The analysis of the waveguide was conducted with three methods: an eigenmode approach, simulation of a truncated structure, and the so-called multimodal transfer matrix method (MMTMM). The presented simulations demonstrate that the operational band can be manipulated by tuning the parameters of the structure. Furthermore, the MMTMM allows for a direct and accurate calculation of the attenuation constant of the rejected circular polarization. Ministerio de Ciencia, Innovación y Universidades TEC2017-84724-P European Union COST Action SyMat CA18223

With research of curved metasurfaces gaining more attention, adequate analysis methods are needed to allow for an efficient design of such structures. Previous works dealt with specific canonical problems, such as those with cylindrical geometry, which were mostly analyzed using Mode Matching approach. In this paper we present an analysis based on Method of Moments which can be used for any generally-curved metasurface structure situated in free-space, or for metasurfaces embedded in canonical multilayer supporting structures (e.g. spherical or cylindrical). We implement a solver for this method and verify the results against other computational approaches, as well as against measurements of a developed antenna pattern-shaping metasurface.

Using glide-symmetric structures with different dispersion properties has shown huge potential for novel electromagnetic applications. Our interest in this paper is to investigate how waveguide-based technology can be improved using glide-symmetric holey structures. The impact which glide-symmetric holey structure has on the waveguide losses when there is an unwanted gap in the waveguide structure is demonstrated using developed prototypes. Further, an analysis of realistic holes with conical endings is performed using developed effective hole length method which can serve as a valuable tool in the process of designing novel waveguide lenses based on these properties.

International audience; Thin artificial surfaces that act as high frequency bandgap structures have been recently studied for the design of gap waveguides, hard surfaces, and planar lenses. Here, we propose a circuit-based method to analyze glide-symmetric corrugated metasurfaces that are embedded in a thin parallel plate waveguide. Our closed-form solution is based on rigorous analytical derivations. It achieves remarkable agreement with full-wave solvers, even when the waveguide thickness is extremely thin. In contrast, classical homogenization approaches are shown to be inaccurate for thin waveguides due to the interaction of higher order Floquet modes between the surfaces. Numerical results validate our theoretical analysis and show the utility of the proposed method.

Vibrations and their parameters can be measured through monitoring the speckle pattern of multimode optical fiber. In this paper a modified approach to realization of a specklegram based vibration sensor system is discussed. Replacing the (standard) camera detector with an array of several detector diodes improves the size and frequency range of the system. Different statistical methods for processing the signals from the diode array are presented, compared experimentally and discussed. The principal advantages of the specklegram vibration detection approach, low cost and distributed detection possibility, have been retained.

Metasurfaces are thin two-dimensional metamaterial layers that allow or inhibit the propagation of electromagnetic waves in desired directions. For example, metasurfaces have been demonstrated to produce unusual scattering properties of incident plane waves or to guide and modulate surface waves to obtain desired radiation properties. These properties have been employed, for example, to create innovative wireless receivers and transmitters. In addition, metasurfaces have recently been proposed to confine electromagnetic waves, thereby avoiding undesired leakage of energy and increasing the overall efficiency of electromagnetic instruments and devices. The main advantages of metasurfaces with respect to the existing conventional technology include their low cost, low level of absorption in comparison with bulky metamaterials, and easy integration due to their thin profile. Due to these advantages, they are promising candidates for real-world solutions to overcome the challenges posed by the next generation of transmitters and receivers of future high-rate communication systems that require highly precise and efficient antennas, sensors, active components, filters, and integrated technologies. This Roadmap is aimed at binding together the experiences of prominent researchers in the field of metasurfaces, from which explanations for the physics behind the extraordinary properties of these structures shall be provided from viewpoints of diverse theoretical backgrounds. Other goals of this endeavour are to underline the advantages and limitations of metasurfaces, as well as to lay out guidelines for their use in present and future electromagnetic devices. This Roadmap is divided into five sections: 1. Metasurface based antennas. In the last few years, metasurfaces have shown possibilities for advanced manipulations of electromagnetic waves, opening new frontiers in the design of antennas. In this section, the authors explain how metasurfaces can be employed to tailor the radiation properties of antennas, their remarkable advantages in comparison with conventional antennas, and the future challenges to be solved. 2. Optical metasurfaces. Although many of the present demonstrators operate in the microwave regime, due either to the reduced cost of manufacturing and testing or to satisfy the interest of the communications or aerospace industries, part of the potential use of metasurfaces is found in the optical regime. In this section, the authors summarize the classical applications and explain new possibilities for optical metasurfaces, such as the generation of superoscillatory fields and energy harvesters. 3. Reconfigurable and active metasurfaces. Dynamic metasurfaces are promising new platforms for 5G communications, remote sensing and radar applications. By the insertion of active elements, metasurfaces can break the fundamental limitations of passive and static systems. In this section, we have contributions that describe the challenges and potential uses of active components in metasurfaces, including new studieson non-Foster, parity-time symmetric, and non-reciprocal metasurfaces. 4. Metasurfaces with higher symmetries. Recent studies have demonstrated that the properties of metasurfaces are influenced by the symmetries of their constituent elements. Therefore, by controlling the properties of these constitutive elements and their arrangement, one can control the way in which the waves interact with the metasurface. In this section, the authors analyze the possibilities of combining more than one layer of metasurface, creating a higher symmetry, increasing the operational bandwidth of flat lenses, or producing cost-effective electromagnetic bandgaps. 5. Numerical and analytical modelling of metasurfaces. In most occasions, metasurfaces are electrically large objects, which cannot be simulated with conventional software. Modelling tools that allow the engineering of the metasurface properties to get the desired response are essential in the design of practical electromagnetic devices. This section includes the recent advances and future challenges in three groups of techniques that are broadly used to analyze and synthesize metasurfaces: circuit models, analytical solutions and computational methods.

The concept of gap waveguide is based on using a finite quasi-periodic structure with an electromagnetic band-gap property to trap waves inside a parallel-plate waveguide. In order to efficiently analyze arbitrary components based on bed-of-nails gap-waveguide technology, we developed an analysis method that rigorously evaluates scattering from each pin using the mode-matching approach in combination with the multiple scattering analysis. The resulting program is very fast making it suitable for iterative optimization in the design process of various components.

In baseband optical communications, information is encoded in the modulated intensity of light propagating over singlemode optical fiber. In radio communications, information is encoded in the phase and amplitude modulation of a signal oscillating at the carrier frequency. This type of modulation can also be employed in optics by creating an intensity modulated beam oscillating a carrier frequency and then modulating the amplitude and phase of this carrier. This paper discusses a preliminary investigation this technology with aim to ultimately apply it to incoherent-light communications by investigating the linearity of a Mach-Zendher optical modulator and an optical link involving QAM-16 modulation over 20-km of singlemode fiber. The conclusion of this work is that without linearization and higher optical power, the system is limited to less than 35 dBc in ACLR and bit-error rate at < 10^-3.

We present a novel electromagnetic bandgap (EBG) structure, which can be used to manufacture low-cost waveguiding structures at high frequencies. The unit cell of the proposed EBG consists of glide-symmetric holes in parallel plate waveguide. Using this unit cell in groove gap waveguide technology has a number of advantages over pin-type EBG at high frequencies, such as acquiring higher accuracy because of larger periodicity as well as an easier and cheaper manufacturing process. The performance of the proposed waveguiding structure is demonstrated using both a straight and a double 90 degrees bent lines through simulation and measurement. This work was supported in part by the Swedish STINT Postdoctoral Transition Grants Programme under Grant PT2014-5813, in part by the Spanish Government under Project TEC2013-44019-R and Project TEC2016-79700-C2-2-R, and in part by the Madrid Regional Government under Project S2013/ICE-3000.

This communication presents an accurate and computationally efficient method for designing spherical lens antennas. The method is based on spherical-wave modal expansion of both the electromagnetic field scattered by a multilayer lens and the far-field radiation pattern of a feed antenna. The two expansions are connected by transforming the fields from the local to the global coordinate system, i.e., by determining the equivalent current sources of the spherical lens Green’s function. An important benefit of this method lies in the simplicity of implementing various feeding antennas in the design process. To verify the method, the results of the analysis are compared with measured radiation patterns of Luneburg lens antennas. Finally, the design guidelines for optimization of the whole lens antenna system are also discussed in the communication.

International audience; This Letter discusses nonresonant modes excited on holey metasurfaces and their influence on the properties of spoof plasmonic states supported by the metasurface when a second surface is placed in its proximity. We consider here a metallic surface with periodic holes drilled in it. The field excited on each hole is projected onto a set of nonresonant modes in order to discuss their relative relevance. While previous simpler models assumed only the presence of the fundamental mode, we show that the simultaneous presence of several modes occurs when the surface is placed next to a metallic plate. Therefore, higher-order modes are responsible for the peculiar physical properties of wave propagation of spoof plasmons between two surfaces, which can lead to new gradient-index flat lenses for transceivers for space communications.

The paper describes a systematic approach and a computer program for designing curved multilayer structures containing metasurface layers. Metasurfaces that manipulate electromagnetic waves have garnered significant attention in recent years. The focus has primarily been on planar devices, however many applications require curved surfaces. Curvature introduces additional challenges in the analysis, and we propose a analysis method based on the surface impedance approach in the spectral domain and on the algorithm for calculating Green's function of multilayer one-dimensional (1D) and two-dimensional (2D) structures.

A novel leaky-wave antenna, realized using gap waveguide concept, is here proposed. Both, the feeding structure and the antenna are realized in groove gap waveguide technology, thus simplifying the whole structure. A complete design procedure, starting from a given groove waveguide to the final radiation mechanism, is described in this communication. The results are supported with measurements of a prototype that operates in the X-band. The realized antenna has a gain around 18 dB between 9 and 11.5 GHz, demonstrating the potential of the proposed radiation technology. This work was supported in part by the Unity through Knowledge Fund (UKF), Croatia, under the project 9/13;, in part by the ESF Research Networking Programme NEWFOCUS, in part by Spanish Government under the project TEC2013-44019-R, and in part by Madrid Regional Government under the project S2013/ICE-3000.

A metasurfing concept is demonstrated and applied in the design of Luneburg lens antennas. Using an array of size-varying circular patches on a dielectric substrate inside a parallel-plate waveguide (PPW) structure variable surface impedance is obtained, which realizes an equivalent refraction index as that of a Luneburg lens. The obtained lens has good bandwidth characteristics and significant fabrication advantages with respect to conventional dielectric lenses. Based on this PPW lens, an H-plane antenna has been designed and simulated.

We propose and theoretically analyze a novel transmitter emitting m wavelength-division multiplexed and independently modulated optical signals. The transmitter is based on an extended cavity formed by m wavelength-agnostic reflective semiconductor optical amplifiers (one for each wavelength) on one end and a single modulation-averaging reflector on the other end of the cavity. We show that optimally designed modulation-averaging reflectors can efficiently change the intensity probability density function from bound bit-stream modulation to a normal distribution and thereby improve signalto- noise ratio of all emitted optical signals. This improvement may potentially allow the realization of cost-efficient wavelength division multiplexing passive optical networks (WDM-PON).

Uniaxial multilayer cylinder cloaks have recently been proposed to prevent scattering of electromagnetic waves. These cloaks are based on spatial variation of constitutive parameters within the structure by means of metamaterials. A mathematical description of invisibility in such cloaks is provided. The analysis approach is based on modal analysis of cylindrical multilayer structures. In order to analyze structures with arbitrary number of layers, an algorithm to calculate spectral-domain Green's functions of uniaxial multilayer structures has been developed. The results show that the recently introduced metamaterial cloaks with reduced variation of constitutive parameters can decrease the total scattering width up to a factor of three, but only in a narrow frequency band due to dispersion in the filling material. Furthermore, it is shown that in the analyzed structures already 6 layers of constant permittivity and permeability approximate well the continuous dependence of constitutive parameters.

A rectangular waveguide filled with anisotropic uniaxial metamaterial with transversal negative effective permeability is investigated both theoretically and experimentally. It is shown that such a waveguide supports propagation of the backward wave below the cutoff frequency, thus, it can be considered as a dual of the ordinary waveguide. The transversal dimension of this waveguide can be arbitrarily smaller than half of a wavelength in the filling material, provided that the transversal permeability is negative. This peculiar behavior may be used for fabrication of miniaturized rectangular waveguides. Several experimental miniaturized waveguides loaded with double ring resonators in 7 GHz frequency band have been designed, fabricated and tested. The measured results revealed backward-wave passband located below the cutoff frequency. Furthermore, it was experimentally shown that the increase of the physical length of the waveguide caused the decrease of the electrical length. This is a direct proof of the backward-wave propagation since the phase of the backward wave increases along the waveguide.

Gap waveguide structures combine the ideas of parallel plate waveguides and electromagnetic bandgaps to form novel efficient high frequency waveguiding structures. Since the concept relies on the use of periodic structures with bandgap properties the analysis is very complex. Our proposed analysis approach is based on efficient use of Method of Moments / Mode-matching to rigorously determine the scattering of each element in the grid. To achieve this, the currents on the elements are first determined by using the Green's function of a single element in a parallel-plate waveguide. The solution is then expanded to all the elements from which dispersion properties can be determined. The results of our approach are verified using full-wave commercial software. They show excellent agreement, but it is important to point out that they are obtained in a fraction of the time compared to the full-wave software.

Modulation-averaging reflectors have recently been proposed as a means for improving the link margin in self-seeded wavelength-division multiplexing in passive optical networks. In this work, we describe simple methods for determining key parameters of such structures and use them to predict their averaging efficiency. We characterize several reflectors built by arraying fiber-Bragg gratings along a segment of an optical fiber and show very good agreement between experiments and theoretical models.

The paper presents an accurate and computationally efficient method for designing spherical lens antennas. The spherical lens is rigorously taken into account by implementing the Green’s functions for the multilayer spherical structures. Important benefit of this method lies in the possibility to implement different types of feeding antennas in the design. This is achieved by transforming the considered feed radiation pattern from its local to the global spherical coordinate system. In order to efficiently implement this transformation the needed coefficients are calculated using Xu’s algorithm. The results of the analysis are compared with measured radiation pattern of a 12 layer Luneburg lens antenna.

This paper presents an overview of complex conical beams and techniques developed for their application in the analysis of reflectors and reflector antenna systems, realised either as full PEC surfaces or quasi-periodic, frequency selective surfaces. The various techniques link complex conical beams with Physical Optics, Spectral-Domain method and the Uniform Theory of Diffraction. The method is tested on several examples, including a frequency-selective dual-reflector system of the Gregorian type, designed for the operating frequency of 25 GHz.

This paper presents a combined analysis approach suitable for analyzing complex reflector antenna systems comprised of both simple PEC reflectors and frequency selective surfaces. The approach joins several methods and models, including Complex Conical Beams, Physical Optics, Spectral-Domain method and the Uniform Theory of Diffraction. The method is tested on a frequency-selective dual-reflector system of the Gregorian type, designed for the operating frequency of 25 GHz.

The purpose of this paper is to study properties of various cylindrical cloak structures where the continuouslyvarying structure is realized as multilayer structure with the stepwise approximation of the constitutive parameters. In order to do that, the developed program for analyzing cylindrical cloaks has been merged with the global optimization routine based on the PSO algorithm. The influence of the selected cost function on the obtained cloak designs are discussed in the paper (minimum of the total scattering width ; maximum obtainable bandwidth ; minimum number of layers, outer cloak radius, angle of arrival of the incidence plane wave, etc.).

Scattering from anisotropic circular-cylindrical objects is rigorously treated for oblique incidence. The system of coupled differential equations for axial components of electromagnetic field arising in this problem is semi-analytically solved: using modal expansion in the axial and circumferential directions and by applying the finite-difference scheme in the radial direction. Developed analysis method is used to characterize different invisibility cloaks and it is demonstrated that realizable cloaks, which were designed for normal incidence, work properly for incidence angles of up to ±10° away from the normal. For angles greater than ±10° away from the normal the cloak should be redesigned, and for that an efficient design approach is realized by merging the developed program with a global optimization algorithm.

Concept of variable or non-uniform metasurfaces allows a very high level of control over the electromagnetic wave paths. In this paper this control is achieved by gradually modifying the geometry of subresonant printed patches on a grounded dielectric substrate. This allows us to change the phase velocity or the propagation path of the guided wave. This property was used to design a Luneburg lens which was then inserted into an H-plane horn to improve the horn's radiation characteristics. The results of this idea are demonstrated using full wave simulations, showing the applicability of this concept.

The purpose of this paper is to study realization feasibility of the cloak structures where the continuously-varying structure is realized as multilayer structure with the stepwise approximation of the constitutive parameters. In order to do that, the influence of the number of cloak layers is investigated, and it is shown that with only three layers it is possible to obtain a better cloak performance than the Schurig cloak (containing ten layers), and that with ten or more layers one can design a cloak that is practically invisible. These results are obtained by merging the program for analyzing uniaxial cylindrical structures with the global optimization program based on the particle swarm optimization algorithm.

This paper demonstrates the properties of an H-plane horn antenna with its characteristics improved using the principle of variable surface impedance. Modifying the surface boundary conditions on one surface of the parallel plate structure is possible by using printed patches of variable size. By doing so, surface impedance profile which corresponds to Luneburg law can be realized. Luneburg lens designed in this way can then be easily implemented inside planar horn antennas to improve their characteristics. The results of this idea are demonstrated using full-wave simulations and show that it is possible to obtain higher horn directivity and significantly reduce the size of the horn within the operational band of the designed Luneburg lens.

Uniaxial cylindrical cloaks have recently been proposed to prevent the scattering of electromagnetic waves, i.e. to render objects invisible. While it is possible to achieve that the rays follow the proper path inside the cloak, the proposed cloaks with reduced variation of constitutive parameters suffer from nonzero reflectance. The purpose of this paper is to improve invisibility performance of the original cloak structure in terms of total scattering width reduction and the operating frequency bandwidth. Therefore, the program for analyzing uniaxial cylindrical structures is merged with the global optimization program based on the particle swarm optimization algorithm. The results show that it is possible either to obtain the “perfect” cloak at the expense of bandwidth or to improve the operating frequency bandwidth at the expense of limited reduction of total scattering width.

Recently, an uniaxial multilayer cylinder cloak which does not scatter electromagnetic wave was proposed. The purpose of this paper is to analyze such a cloak and to characterize the achieved “ invisibility” in mathematical terms by calculating the scattered field and equivalent blockage width – the structure width that is actually “ perceived” by EM waves. For that purpose we have developed the G1DMULT algorithm for analyzing uniaxial multilayer structures of planar, circular – cylindrical and spherical shape. The results show that the analyzed metamaterial realization reduces the scattered field and is suitable only for excitation by a TM-polarized wave. Furthermore, due to the dispersion it works only in a narrow frequency band. It seems that analyzed structure is inferior to already known realizations of invisibility, e.g. by hard surfaces that can work for arbitrary polarization within larger frequency bandwidth, although suitable for only one direction of incoming wave.

The purpose of this paper is to present a fiber- optic vibration sensor based on the monitoring of the mode distribution in a multimode optical fiber. Detection of vibrations and their parameters is possible through observation of the output speckle pattern from the multimode optical fiber. A working experimental model has been built in which all used components are widely available and cheap: a CCD camera (a simple web-cam), a multimode laser in visible range as a light source, a length of multimode optical fiber, and a computer for signal processing. Measurements have shown good agreement with the actual frequency of vibrations, and promising results were achieved with the amplitude measurements although they require some adaptation of the experimental model. Proposed sensor is cheap and lightweight and therefore presents an interesting alternative for monitoring large smart structures.

Recently, an uniaxial multilayer cylinder cloak which does not scatter electromagnetic wave was proposed. However, the metamaterial realization only reduces the scattered field and is suitable only for excitation by a TM-polarized wave. Furthermore, it works only in a narrow frequency band. The purpose of this paper is to analyze such a cloak and to characterize the achieved “ invisibility” in mathematical terms by calculating the scattered field and equivalent blockage width – the structure width that is actually “ perceived” by EM waves. Therefore, mathematical analysis for TM-excitation is provided and the simulations are performed using the G1DMULT algorithm. The results show large sensitivity of reduction in the equivalent blockage width on the number of anisotropic layers used for cloak realization.

The numerical models of optical fiber, amplifier and filter we developed is given. The computer program for simulating an optical link based on these models is described. Selected simulation results of high bit-rate optical links are given (dispersion compensating link, classical and dispersion-managed soliton transmission links)

A novel remote fiber testing system (RFTS) for error detection in optical networks is presented in this paper. The proposed measurement system is applicable to access and local optical networks for which the standard RFTS is too expensive. The basic idea lies in replacing expensive optical switches with more affordable optical power splitters. Consequently, all fibers are simultaneously tested and therefore the new method for error detection is developed. The experimental results demonstrate the possibilities of the new testing system.

In recent years, the need for omnidirectional (in the azimuthal plane) antennas with narrow beams in the elevation plane, for wireless applications increased considerably. The antennas are used in amny frequency bands anywhere from 0.8 to 6 GHz. In a variety of configurations. The different collinear-array configurations are designed using back-to-back wide-beam elements or by simply using radiating elements with an intristic omnidirectional pattern. The motivation for this work was to devise a radiation element which (a) has an omnidirectional pattern in the azimuth plane, (b) allows for the design and fabrication of arrays, that can be easily integrated with other collinear arrays to generate a multitasking omnidirectional antenna. The element proposed in this paper is patch, which was built in a cylindrical geometry rather than a planar one, and which generates an omnidirectional pattern in the azimuthal plane.

The material contained in this paper is intended to help determine the feasibility of using a spherical lens as a low sidelobe multiple beam antenna. It includes what are deemed the most relevant points of a more thorough investigation. We consider the constant-k lens and the Luneberg lens. The constant-k lens, as the name implies, is a homogeneous dielectric sphere. R.K. Luneberg proposed the Luneberg lens in 1944. Morgan (1960) derived a general class of Luneberg lenses that focus from one arbitrary point source to another. In the 50s and 60s antenna designers applied Luneberg lenses to a wide variety of antenna and scattering applications. The array feed used to illuminate the lens has its surface on a sphere with a radius equal to, or larger than, the outer radius of the lens. Each element of the array forms an independent beam. These beams are combined to form a new beam with lower sidelobes.

The asymptotic corrugation boundary condition (ACBC) presented previously is improved in this paper by introducing in the analysis the ratio of the corrugation width to the corrugation period. The ACBC is also validated through comparisons with the exact Floquet mode expansion technique for the case of corrugated circular cylinders. Excellent agreement is obtained between the two solutions for small periods. The ACBC is actually asymptotically correct when the corrugation period approaches zero. It is also an extension of a similar asymptotic strip boundary condition (ASBC), which was previously used to analyze scattering from strip-loaded dielectric cylinders. The ACBC is based on approximating the field expressions inside the grooves of the corrugations and enforcing an asymptotic boundary condition at the interface to the outer region. It is valid in the limit at which the corrugation period is zero.

We develop the Green's functions for different realizations of planar soft and hard surfaces by using the asymptotic boundary conditions and the spectral domain approach. The considered geometries are the ideal PEC/PMC strip surface, the strip-loaded grounded dielectric slab and the corrugated surface. In all cases the strips and corrugations are straight. The asymptotic boundary conditions are valid in the limiting sense, when the period of the strips or corrugations approaches zero. The developed Green's functions have poles corresponding to surface waves. These are of three types: an ordinary surface wave in the grounded dielectric slab propagating radially out from the source, a strip wave propagating along the strips of the strip-loaded dielectric slab and also along the strips of the PEC/PMC strip surface, and surface waves occurring due to the corrugated surface. The fulfillments of both the soft and hard boundary conditions are discussed in both the near and far field regions. The strip wave of the strip-loaded dielectric slab prevents the boundary conditions in the near-field from being fulfilled, and is thus undesired. The other two surface waves are needed in order to realize the hard boundary condition. This paper is done while Zvonimir Sipus was a Ph.D. Student at Chalmers University of Technology, Gothenburg, Sweden

The paper presents the analysis of cylindrical and spherical structures used for invisible cloak realization. Different cylindrical and spherical cloak realizations were analyzed in terms of bistatic scattering cross section. In addition, optimization algorithm was connected with the analysis routine to find the constitutive parameters of the cloak that reduce both backscattering and forward scattering. The results show that it is possible to obtain adequate invisibility performance by covering the PEC sphere with only 2 thin anisotropic layers.

A rectangular waveguide filled with anisotropic uniaxial meta-material with transversal negative effective permeability is analyzed rigorously. It is shown that such waveguide supports propagation of backward wave below the cut-off frequency, thus, it can be considered as a dual of an ordinary waveguide. The transversal dimension of the waveguide can be arbitrarily smaller than a half of the wavelength, which may be used for fabrication of miniaturized rectangular waveguides. Several experimental miniaturized waveguides filled with different resonant meta-materials in the 7 GHz and 350 MHz frequency bands have been designed, fabricated and tested. The measured results revealed backward-wave pass-band located below the cut off frequency, which is in agreement with theoretical analysis.

The recently introduced concept of one-dimensional subwavelength resonator, which comprises a combination of forward-wave material and backward-wave material, is investigated experimentally. The rectangular evanescent waveguide filled with negative permeability uniaxial meta-material based on capacitively loaded loop was used as backward-wave meta-material in 350 MHz band. The waveguide was interfaced with an ordinary (forward-wave) coaxial transmission line terminated with a sliding short. The overall length of this waveguide-coaxial structure was much shorter than the wavelength. The distribution of the phase of the magnetic field along the structures was measured with the help of a small loop antenna and network analyzer, for different settings of the sliding short. The measurement results proved that is possible to meet resonant conditions on the structure whose overall length is much smaller than a wavelength, as it was previously theoretically predicted.

Uniaxial cylindrical cloaks have recently been proposed to prevent scattering of electromagnetic waves, i.e. to render objects invisible. In this paper frequency and time domain analysis of such a cloak has been carried out. Furthermore, influence of number of cloak layers on obtained invisibility has been studied, with special attention given to the cloak with just three layers that should be relatively easy to practically realize.