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Now showing items 1 - 16 of 37

  • Modeling of Glide-Symmetric Dielectric Structures

    Sipus, Zvonimir   Bosiljevac, Marko  

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  • Roadmap on metasurfaces

    Quevedo-Teruel, Oscar   Chen, Hongsheng   Díaz-Rubio, Ana   Gok, Gurkan   Grbic, Anthony   Minatti, Gabriele   Martini, Enrica   Maci, Stefano   Eleftheriades, George V   Chen, Michael   Zheludev, Nikolay I   Papasimakis, Nikitas   Choudhury, Sajid   Kudyshev, Zhaxylyk A   Saha, Soham   Reddy, Harsha   Boltasseva, Alexandra   Shalaev, Vladimir M   Kildishev, Alexander V   Sievenpiper, Daniel   Caloz, Christophe   Alù, Andrea   He, Qiong   Zhou, Lei   Valerio, Guido   Rajo-Iglesias, Eva   Sipus, Zvonimir   Mesa, Francisco   Rodríguez-Berral, Raul   Medina, Francisco   Asadchy, Victor   Tretyakov, Sergei   Craeye, Christophe  

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  • An Insight into Creeping Electromagnetic Waves around the Human Body

    Ivsic, Branimir   Bonefacic, Davor   Sipus, Zvonimir   Bartolic, Juraj  

    The electromagnetic wave propagation around human body torso is modelled by considering elementary electric and magnetic dipoles over an infinite muscle-equivalent cylinder. The poles in the spectral domain Green's function with smallest imaginary part are found to correspond to creeping wave propagation coefficients which predict the general trend in propagation around human body. In addition, it was found that axial magnetic field component is crucial for communication via creeping waves since it generates modes with smaller field decay compared to axial electric field. The developed model may thus serve as a practical guideline in design of on-body wearable antennas. The theoretical considerations are verified with simulations and measurements on the prototype of PIFA antenna placed on the human body.
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  • Useful Physical Images and Algorithms for Vector Dyadic Green's Functions

    Kildal, Per-Simon   Sipus, Zvonimir   Yang, Jian   Maaskant, Rob  

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  • Gap Waveguide Leaky-Wave Antenna

    Vukomanovic, Mladen   Vazquez-Roy, Jose-Luis   Quevedo-Teruel, Oscar   Rajo-Iglesias, Eva   Sipus, Zvonimir  

    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.
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  • Simple Boundary Condition for Canonical EBG Surface:PMC-Backed Uniaxial Medium

    Bosiljevac, Marko   Sipus, Zvonimir   Kildal, Per-Simon   Freni, Angelo  

    A simple-to-use replacement model for isotropic electromagnetic bandgap (EBG) surfaces such as mushroom surfaces is investigated. Properties of EBG surfaces strongly depend on the incidence angle of the incoming plane wave. The suggested model takes this behavior into account and actually represents the ideal EBG surface. The model is based on uniaxial representation of a thin DB layer backed by a perfect magnetic conductor (PMC) plate. We investigate how this model behaves in comparison with a realistic mushroom surface, and when it can be applied. The results show that the proposed model can be used for both far field calculations and antenna coupling evaluation.
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  • Fundamental Limits for Implanted Antennas: Maximum Power Density Reaching Free Space

    Skrivervik, Anja K.   Bosiljevac, Marko   Sipus, Zvonimir  

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  • Accurate Equivalent-Circuit Descriptions of Thin Glide-Symmetric Corrugated Metasurfaces

    Valerio, Guido   Sipus, Zvonimir   Grbic, Anthony   Quevedo-Teruel, Oscar  

    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.
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  • Modulation-Averaging Reflectors for Extended-Cavity Optical Sources

    Komljenovic, Tin   Babic, Dubravko   Sipus, Zvonimir  

    We propose and theoretically analyze a novel transmitter emitting wavelength-division multiplexed and independently modulated optical signals. The transmitter is based on an extended cavity formed by 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 signal-to-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).
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  • Characterization and Reduction of Mutual Coupling Between Stacked Patches

    Quevedo-Teruel, Oscar   Sipus, Zvonimir   Rajo-Iglesias, Eva  

    A rigorous analysis of mutual coupling between stacked patches is proposed in this work. The considered stacked-patch configuration has a dielectric-air-dielectric topology, and the level of mutual coupling has been related to the working region, which is defined depending on the gain and frequency bandwidth of the antenna, as well as on the shape of the radiation pattern. For certain antenna parameters a dip appears in the mutual coupling characteristic, and detailed study of this phenomenon has been carried out. Since this dip in the mutual coupling depends on the resonant frequency of the parasitic patch, it can be used to reduce the mutual coupling in the operational frequency bandwidth of the antenna. We have developed an experimental model that has proven this concept of antenna coupling reduction. Finally, the influence of other antenna parameters on the mutual coupling level has been studied.
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  • Acceleration of Series Summation Encountered in the Analysis of Conformal Antennas

    Sipus, Zvonimir   Bosiljevac, Marko   Sipus, Zeljka Milin  

    Complexity and needed computation time of moment method analysis approach for conformal antennas is reduced by applying particular series acceleration techniques to the partial sums encountered in these problems. The Wynn's epsilon-acceleration technique is investigated and modified in order to achieve better convergence. The results show excellent convergence properties when applying this method in the analysis of antennas printed on cylindrical and spherical substrates.
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  • Electromagnetic Modeling of Spherically Stratified Lenses Illuminated by Arbitrary Sources

    Sipus, Zvonimir   Bojanjac, Dario   Komljenovic, Tin  

    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.
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  • Study of mutual coupling between circular stacked-patch antennas on a sphere

    Sipus, Zvonimir   Skokic, Sinisa   Bosijevac, Marko   Burum, Niksa  

    dAbstract-A rigorous mathematical analysis is given of spherical stacked-patch arrays with emphasis on the physical interpretation of mutual coupling mechanisms present in doubly-curved convex structures. The analysis method is based on electromagnetic field representation in terms of spherical harmonics where each harmonic has the same angular variation as the spectral source component. To obtain the spectral representation the vector-Legendre transformation is applied to currents and fields. A novel approach to the mutual coupling calculation within the method of moments analysis of spherical arrays is applied. By expressing the patch current in terms of two suitable potential-like auxiliary functions, it is possible to avoid the use of Euler's formulas for coordinate system rotation and the related lengthy integrations. Instead, the rotation of antenna elements and corresponding current distributions can be done in closed form with the help of Vilenkin's addition theorem for associated Legendre functions. It is shown that the new approach results in significant acceleration and improved accuracy of the analysis of spherical patch antenna arrays. The algorithm is successfully tested against a commercially available electromagnetic software and measurements performed on the developed laboratory model, confirming its accuracy for both input impedance and mutual coupling calculation and with only a small between the predicted and measured resonant frequencies, due to limitations in the experimental model. The influence of the structure parameters on mutual coupling level is extensively investigated, including all coupling mechanisms and leakage of energy due to curvature of the structure. It is shown that stacked-patch antennas can have reduced coupling level comparing to single patch antennas with possible deep nulls above the antenna resonant frequency.
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  • Layered Circular-Cylindrical Dielectric Lens Antennas-Synthesis and Height Reduction Technique

    Komljenovic, Tin   Sauleau, Ronan   Sipus, Zvonimir   Le Coq, Laurent  

    An accurate computer-aided-design tool has been developed for the synthesis of broadband layered circular-cylindrical dielectric lens antennas. It is based on the combination of a fast method of analysis formulated in the spectral domain with a global optimization algorithm based on the particle swarm optimization technique. Using this tool, the influence of the number of layers is studied for lenses of moderate size. We show that single-layer lenses with an optimum permittivity value have nearly the same radiation characteristics as optimized multi-layer configurations. Finally we introduce a new height reduction technique that allows reducing the lens size by almost a factor of two while retaining the fan-beam pattern capabilities of cylindrical lenses in the elevation plane as well as their axial-symmetry needed for beam scanning in the horizontal plane. Numerical results have been compared successfully with experimental ones from 26 to 40 GHz, to validate the analysis.
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  • Modelling cascaded cylindrical metasurfaces using sheet impedances and a transmission matrix formulation

    Sipus, Zvonimir   Bosiljevac, Marko   Grbic, Anthony  

    Metasurfaces that manipulate electromagnetic waves have gained significant attention in recent years. The focus has primarily been on planar devices, while many applications require curved surfaces. In this study, the authors propose an analysis approach for cylindrical cascaded (multilayer) metasurfaces. The approach combines the concept of sheet impedance in the spectral domain with a new transmission matrix formulation that is applicable to stratified, canonical curved geometries. Approximate formulas for the sheet impedance of common planar, metallic patterns are also adapted to curved geometries. The reported analysis approach allows one to determine the optimal spectral-domain, azimuthal dependence of a sheet impedance, as well as the best geometrical elements to obtain the required azimuthal variation. The results are verified through several cylindrical metsurface examples.
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  • Reply to "Comments on 'Waveguide miniaturization using uniaxial negative permeability metamaterial"'

    Hrabar, Silvio   Bartolic, Juraj   Sipus, Zvonimir  

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