The present work aims at an eigenanalysis methodology for lossy or open periodic structures incorporating the Floquet fleld expansion within the FDFD formulation. For that case, a fl-eigenvalue problem is formulated but this leads to a... more
The present work aims at an eigenanalysis methodology for lossy or open periodic structures incorporating the Floquet fleld expansion within the FDFD formulation. For that case, a fl-eigenvalue problem is formulated but this leads to a non linear eigenvalue problem. Difierent eigenvector | eigenvalue transformations are currently tried in order to remove the nonlinearity. Periodic structures resulting to negative refractive index comprised of magnetized ferrite slabs and dipole arrays are considered as particular examples. 1. INTRODUCTION The unique electromagnetic features of periodic structures attracted a huge research interest dur- ing the last decades. These features enabled the development of novel metamaterials and were exploited in frequency selective surfaces, phased arrays and numerous electromagnetic bandgap applications. The analysis and design of such structures have received particular attention which is almost exclusively directed toward the deterministic numerous simulations. Namely, an electromag- netic simulation of periodic structure excited by a speciflc source. Even though this analysis served as a very useful tool, it does not ofier the required physical insight, while it does not provide any means to devise novel structures. On the other hand, an eigenanalysis reveal the physical behavior of the structure. In particular, the resulting eigenfunctions can be exploited to devise novel features and enable multifunctionality of periodic structures. Besides, a variety of microwave applications and in particular conformal antennas with their beamforming networks, require a simulation tool capable of handling periodic structures loaded with inhomogeneous and anisotropic media. An appropriate eigenanalysis for the three-dimensional waveguiding periodic structures was developed in our previous work (1), which was able to handle anisotropic media. For this analysis a Finite Difierence Frequency Domain (FDFD) method was employed in orthogonal Curvilinear Coordinates Yee type mesh (2). At this flrst attempt the eigenvalue problem was formulated and solved for the eigenfrequencies (!-formulation) or the wavenumber. Namely, the range of a real valued (ignoring losses or radiation) Floquet wavenumber was deflned and scanned in an iterative solution procedure. This procedure yields the Bloch diagrams. However this kind of !-formulation is restricted to closed periodic structures, since we assume the propagation constant to be real. The present work aims at an eigenanalysis methodology for lossy or open periodic structures incorporating the Floquet fleld expansion within the FDFD formulation. The !-formulation of such geometries requires the knowledge of the range of values for the phase and especially attenuation constants which are the unknowns to be sought. For that case, a fl-eigenvalue problem is formu- lated and solved for the complex propagation constants (eigenvalues) with the Arnoldi iterative Algorithm. The periodicity of the structure is accounted through the incorporation of Floquet Field Expansion within the FDFD formulation. The boundary conditions are in turn imposed on the remaining surfaces of the unit cell and especially at the interface with free space, where an artiflcial-separation absorbing boundary is introduced. For that case, the Absorbing Boundary Conditions (ABCs) or the Perfect Matching Layers (PML) are usually assumed but this approach results to unwanted spurious eigenvalues, the so-called Berenger modes. One of the future tasks of this research aims at overcoming this drawback through exact-global truncation techniques. The main di-culty encountered in the fl-formulation is that the eigenproblem becomes non linear and this constitutes the main drawback of the presented approach. However, due to the important applications that can be supported, it worth to deal with this complexity.
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The Characteristic Mode analysis of a drop-like supershaped patch antenna constitutes the main scope of this project. Supershapes are abstract shapes generated by J. Gielis' Superformula and are used as radiators with wideband... more
The Characteristic Mode analysis of a drop-like supershaped patch antenna constitutes the main scope of this project. Supershapes are abstract shapes generated by J. Gielis' Superformula and are used as radiators with wideband properties. The eigenanalysis is performed on the PMCHWT formulated MoM-matrix, derived from the combined field integral equation. The characteristic modes are analyzed via the equivalent magnetic characteristic currents on the printed antenna aperture surface of the cavity-like subdomain of the simulated structure.
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As fifth generation (5G) wireless communication systems roll out, significant challenges exist towards the design of critical hardware, that is needed in order to realize the performance goals of 5G systems. One such challenge is the... more
As fifth generation (5G) wireless communication systems roll out, significant challenges exist towards the design of critical hardware, that is needed in order to realize the performance goals of 5G systems. One such challenge is the development of antenna arrays with multiple beams. This work, proposes the design of a mm-Wave beamforming network based on a modified Blass matrix architecture, which is loaded with appropriately designed cross couplers. The proposed implementation shows a constant time delay in the 27.5-32.5 GHz frequency band.
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The current work focuses on the study of tunable THz open structures, establishing an eigenmode analysis based on an in-house developed finite element code. The key feature of this numerical tool is the modification of eigenanalysis... more
The current work focuses on the study of tunable THz open structures, establishing an eigenmode analysis based on an in-house developed finite element code. The key feature of this numerical tool is the modification of eigenanalysis formulation for the study of microwave structures, in order to meet the requirements for the study of devices operating at THz regime. The eigenmodes of tunable THz nanoantennas will be studied to reveal their characteristics and devise a design approach. For the truncation of the open-unbounded domain, the first order absorbing boundary conditions will be employed, while the occurring spurious modes will be eliminated with the incorporation of a tree-cotree technique. The tunability of the studied structures will be evaluated in a rather innovative approach as a piecewise constant distribution for the electro-optically controlled dielectric constant.
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In this paper a phased array consisting of eight tightly coupled parallel dipoles is studied. The array is placed adjacent to the human body in an attempt to define the effects of its dielectric constant and losses on the array design.... more
In this paper a phased array consisting of eight tightly coupled parallel dipoles is studied. The array is placed adjacent to the human body in an attempt to define the effects of its dielectric constant and losses on the array design. The analysis of the array is carried out with characteristic modes. The ultimate scope of this effort aims at the establishment of an orthogonal eigencurrent basis, which will be exploited in the synthesis of desired radiation patterns. Its novel aspect refers to the pattern synthesis in the presence of lossy Human body.
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Eigenanalysis of canonically shaped structures served as an indispensable tool the conception and establishment of a plethora of electromagnetic structures from filters to cavities and antennas. However, the recent evolution of radio... more
Eigenanalysis of canonically shaped structures served as an indispensable tool the conception and establishment of a plethora of electromagnetic structures from filters to cavities and antennas. However, the recent evolution of radio systems and wireless communications ask for the design of multifunctional rf front-ends in compact form and conformally integrated on mobile devices. The eigen-analysis features could again support this evolution but could only be performed numerically. It is toward this ambitions aims that our research effort is directed during the last years. This article presents an overview of the related work, which is based on finite difference, finite element, mode matching and moment method. The applications elaborated include closed as well as open-radiating structures loaded with inhomogeneous and/or anisotropic media. Particular effort is devoted to external eigenmodes and characteristic modes, especially for antenna design.
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The establishment of a rigorous full-wave eigenanalysis based on finite element method as numerical tool for the understanding and the revealing the characteristics of Terahertz nano-antennas, constitutes the scope of the current work. A... more
The establishment of a rigorous full-wave eigenanalysis based on finite element method as numerical tool for the understanding and the revealing the characteristics of Terahertz nano-antennas, constitutes the scope of the current work. A tree-cotree splitting formulation method is incorporated for the suppression of all types of spurious modes. An indicative example of a gold nanodimer structure is studied by evaluating its eigenvalues and eigenvectors. First kind absorbing boundary conditions are adopted for the truncation of the infinite solution domain. To understand this nano-antenna behavior the same structure is analyzed when scaled down to the microwave frequencies. The numerical results obtained for the THz and microwave rigimes are compred between them while the THz ones are against related published results.
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A three dimensional Mode Matching/Collocation technique is proposed in the current work for the analysis of a general cavity loaded with a spherical inhomogeneity. Analytical electromagnetic field eigen-solutions expressed in terms of... more
A three dimensional Mode Matching/Collocation technique is proposed in the current work for the analysis of a general cavity loaded with a spherical inhomogeneity. Analytical electromagnetic field eigen-solutions expressed in terms of spherical wave functions are utilized for the field expansions. The boundary conditions on the spherical surface are enforced through the collocation method. Analytical results are obtained for both the source driven problem and the corresponding eigen-problem, i.e. the eigenfunctions of the whole inhomogeneous geometry. The proposed theory will be utilized modelling in biomedical structures and especially in microwave ablation. The contribution of the current work is the use of entire domain basis functions that provide performance improvements especially for electrically medium to large domains. Results, including finite domains, following coordinate or non-separable surfaces, inside spheroids, paraboloids and elliptic cones, have been extracted and ...
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In this work, we present a rigorous full-wave eigenanalysis for the study of nanoantennas operating at both terahertz (THz) (0.1–10 THz), and infrared/optical (10–750 THz) frequency spectrums. The key idea behind this effort is to reveal... more
In this work, we present a rigorous full-wave eigenanalysis for the study of nanoantennas operating at both terahertz (THz) (0.1–10 THz), and infrared/optical (10–750 THz) frequency spectrums. The key idea behind this effort is to reveal the physical characteristics of nanoantennas such that we can transfer and apply the state-of-the-art antenna design methodologies from microwaves to terahertz and optics. Extensive attention is given to penetration depth in metals to reveal whether the surface currents are sufficient for the correct characterization of nanoantennas, or the involvement of volume currents is needed. As we show with our analysis, the penetration depth constantly reduces until the region of 200 THz; beyond this point, it shoots up, requiring volume currents for the exact characterization of the corresponding radiating structures. The cases of a terahertz rectangular patch antenna and a plasmonic nanoantenna are modeled, showing in each case the need of surface and volu...
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A procedure for calculating the characteristic modes series and parallel resonances calculation based on finite element method (FEM), in contrast to the established use of Method of Moment (MoM) is developed. A characteristic mode... more
A procedure for calculating the characteristic modes series and parallel resonances calculation based on finite element method (FEM), in contrast to the established use of Method of Moment (MoM) is developed. A characteristic mode formulation based on electric currents yields only the series resonances of the analyzed structure. The direct calculation of the parallel resonances becomes feasible with the usage of the equivalent magnetic current characteristic modes. For this purpose the finite element method formulation we have recently established is employed. This is able to handle open-radiating structures even loaded with anisotropic media, it utilizes absorbing boundary conditions for truncating the unbounded domain, while it eliminates the DC and imaginary spurious modes. This is now employed for two alternative approaches. For the first the eigenproblem is reformulated in order to retain only the degrees of freedom of tangential magnetic field on the surface of the metallic parts or the electric currents and thus to yield the related impedance matrix [Z]. In the alternative formulation the tangential electric field over the radiating apertures or the equivalent magnetic currents are retained to yield the structures admittance matrix [Y]. In both cases the characteristic modes scheme separating [Z] and [Y] into real and imaginary parts is employed to formulate respective real eigenproblems. These are solved for the eiegencurrents with particular emphasis in the direct estimation of the series for electric and parallel resonances for magnetic eigencurrents respectively. Example for different antennas at series and parallel resonance are depicted as validations.
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A two dimensional Finite Difference Frequency Domain (2D-FDFD) eigenanalysis of an array consisting of periodically located strips printed on axially magnetized ferrite film is presented. The main interest in these structures arises from... more
A two dimensional Finite Difference Frequency Domain (2D-FDFD) eigenanalysis of an array consisting of periodically located strips printed on axially magnetized ferrite film is presented. The main interest in these structures arises from our previous study which revealed their support of backward surface and possibly backward leaky waves. Moreover these structures exhibit non-reciprocal phenomena. These phenomena are studied thoroughly by using our two - dimensional curvilinear frequency domain finite difference (2D-FDFD) method, modified appropriately for the eigenanalysis of periodic structures. The present effort is particularly focused on the study of the non-reciprocal phenomena involved in periodic structures loaded with magnetized ferrites.
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It is of critical importance to efficiently and accurately evaluate both the internal and external resonances of three dimensional closed and open-radiating structures. Regarding the polynomial eigenvalue problem for the case of both... more
It is of critical importance to efficiently and accurately evaluate both the internal and external resonances of three dimensional closed and open-radiating structures. Regarding the polynomial eigenvalue problem for the case of both lossy and open radiating structures the spurious modes are being suppressed by appropriately enforcing the “divergence-free” constraint equations over the whole domain. For the spurious modes suppression, two newly presented techniques are implemented and tested for the first time in conjunction with both direct and iterative solvers exploiting Arnoldi algorithm.
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The current work is the theoretical framework of the Research Project “Thales” entitled: “Development of electromagnetic simulation and design tools for digitally controlled and multifunctioning RF-microwave stages and subunits which... more
The current work is the theoretical framework of the Research Project “Thales” entitled: “Development of electromagnetic simulation and design tools for digitally controlled and multifunctioning RF-microwave stages and subunits which retain characteristics-specification supporting Software Defined (SDR) and cognitive Radios (CR)”. Thus, a review of the analytical and numerical eigenenalysis tools developed and used under the framework of this project is presented herein. An abstract description of these methods in addition with some indicative results is thus presented.
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Research Interests: Physics and Surface Wave
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A generalization of the tree-cotree technique for the removal of imaginary and dc spurious modes in finite-element-based eigenanalysis of 3-D lossy unbounded structures is introduced. Five frequently encountered types of polynomial... more
A generalization of the tree-cotree technique for the removal of imaginary and dc spurious modes in finite-element-based eigenanalysis of 3-D lossy unbounded structures is introduced. Five frequently encountered types of polynomial eigenvalue problems are tackled including: 1) closed structures with finite metals conductivity losses; 2) closed structures with material losses due to migrating charge carriers; 3) open-radiating structures using the absorbing boundary conditions of both first- and second-order; 4) open-radiating structures with finite conductivity metallic objects; and 5) any combination of the aforementioned cases. The resulting polynomial eigenvalue problems are linearized utilizing both the companion and the symmetric approaches. The different linearization techniques are being compared for their efficiency and robustness.
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In this work the performance and behavior of nonlinear eigenanalysis algorithms on formulation based on the Finite Element Method (FEM) is investigated for structures operating in THz. A technique like the tree-cotree splitting... more
In this work the performance and behavior of nonlinear eigenanalysis algorithms on formulation based on the Finite Element Method (FEM) is investigated for structures operating in THz. A technique like the tree-cotree splitting formulation method for the suppression of non-physical solution, the enhancement of the numerical stability and efficiency, is incorporated. Accurate global mesh truncation techniques are also adopted and refined for the eigenanalysis of open structures.
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This work addresses a beam steering scheme for RFID readers. The proposed architecture uses a double Butler matrix network configuration in order to provide polarization diversity to the antenna array. The array is placed on a faceted... more
This work addresses a beam steering scheme for RFID readers. The proposed architecture uses a double Butler matrix network configuration in order to provide polarization diversity to the antenna array. The array is placed on a faceted surface, aiming at a coverage sector increase. Circuit architecture and simulation results are presented.
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In this paper a three dimensional Mode Matching technique is proposed for the analysis of a spheroidal cavity loaded with a spherical inhomogeneity around one of its focuses. Analytical electromagnetic field eigen-solutions expressed in... more
In this paper a three dimensional Mode Matching technique is proposed for the analysis of a spheroidal cavity loaded with a spherical inhomogeneity around one of its focuses. Analytical electromagnetic field eigen-solutions expressed in terms of spheroidal and spherical wave functions are utilized for the field expansions. The boundary conditions on the spherical surface are enforced through a coordinate transformation and the related Hankel functions addition theorem. Analytical results are obtained for both the source driven problem and the corresponding eigen-problem, i.e. the eigenfunctions of the whole inhomogeneous geometry are obtained. The proposed theory will be utilized in the modelling of biomedical structures and especially in microwave ablation.
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An eigenanalysis of an array of periodically located wires covered with axially magnetized ferrites is presented. The interest in this structure stems from our previous study which revealed that such a wire may support backward surface... more
An eigenanalysis of an array of periodically located wires covered with axially magnetized ferrites is presented. The interest in this structure stems from our previous study which revealed that such a wire may support backward surface and possibly backward leaky waves. These possibilities are examined herein by using our two - dimensional curvilinear frequency domain finite difference (FDFD) toward the eigenanalysis of periodic structures. The analysis is focused not only in in-plane wave propagation but also in out of plane wave propagation where the propagation constant along the z axis is different than zero.
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An eigenanalysis of an array of periodically located wires covered with axially magnetized ferrites is presented. The interest in this structure stems from our previous analytical study which revealed that such a wire may support backward... more
An eigenanalysis of an array of periodically located wires covered with axially magnetized ferrites is presented. The interest in this structure stems from our previous analytical study which revealed that such a wire may support backward surface and possibly backward leaky waves. It is thus expected that a periodic array of these ferrite loaded wires may behave as a backward wave media offering an equivalent negative index of refraction as well as electromagnetic band gaps. These possibilities are examined herein by extending our previous two - dimensional curvilinear frequency domain finite difference method (FDFD) toward the eigenanalysis of periodic structures. Initially, the periodicity is accounted through periodic boundary conditions, while latter the related Floquet expansion will be introduced within the FDFD formulation.
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Millimeter wave (mm-Wave) technology is likely the key enabler of 5G and early 6G wireless systems. The high throughput, high capacity, and low latency that can be achieved, when mm-Waves are utilized, makes them the most promising... more
Millimeter wave (mm-Wave) technology is likely the key enabler of 5G and early 6G wireless systems. The high throughput, high capacity, and low latency that can be achieved, when mm-Waves are utilized, makes them the most promising backhaul as well as fronthaul solutions for the communication between small cells and base stations or between base stations and the gateway. Depending on the channel properties different communication systems (e.g., beamforming and MIMO) can accordingly offer the best solution. In this work, our goal is to design millimeter wave beamformers for switched beam phased arrays as hybrid beamforming stages. Specifically, three different analog beamforming techniques for the frequency range of 27–33 GHz are presented. First, a novel compact multilayer Blass matrix is proposed. Second, a modified dummy-ports free, highly efficient Rotman lens is introduced. Finally, a three-layer true-time-delay tree topology inspired by microwave photonics is presented.
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In this article a reconfigurable antenna for WLAN/WiMAX applications is presented. A super-shape radiator of an ellipsis shape is used to achieve wider intrinsic bandwidth compared to the classical rectangular patch antenna, while the... more
In this article a reconfigurable antenna for WLAN/WiMAX applications is presented. A super-shape radiator of an ellipsis shape is used to achieve wider intrinsic bandwidth compared to the classical rectangular patch antenna, while the dimensions remain comparable. The proposed antenna is fed at two points exciting both horizontal and vertical polarization but in different operating frequencies. To achieve wider bandwidth, as a whole but also for each polarization, the symmetrical feeding points for each excitation are also employed with a proper feeding network. PIN diodes are also used in the feeding network to provide the option of narrower bandwidth. The antenna substrate is Rogers RO4003C with dielectric constant εr = 3.55 and dissipation losses tanδ = 0.0027 with height h = 1.524 mm. The antenna operates in the range of 2.3 GHz to 2.55 GHz but, using the proposed procedure, it can be designed for different frequency ranges.
Research Interests: Physics and Electronics
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A very powerfull tool first to device an appropriate geometry and then to design the related MIMO antenna is introduced based on the "characteristic modes" eigenanalysis. The ultimate task of this methodology refers to the... more
A very powerfull tool first to device an appropriate geometry and then to design the related MIMO antenna is introduced based on the "characteristic modes" eigenanalysis. The ultimate task of this methodology refers to the formulation of a mobile unit chassis into a multifunctional MIMO antenna. The numerical evaluation of the complex impedance matrix after its split into its real and imaginary part provides valuable physical insight of the structure. It is proved that a surface current density mode eigencurrent is at resonance when its associated eigenvalue is zero. Explicitly the smaller the magnitude of the eigenvalue is, the more efficiently the mode radiates when is excited. Moreover, the corresponding eigencurrent distribution defines the radiation characteristics including its radiation pattern and its polarization. Examining the eigencurrent distribution over the structure the appropriate excitation type and its location can be selected.
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The establishment of finite element based eigenanalysis as a numerical tool for the indepth understanding and revealing the characteristics of Terahertz and photonic structures, constitute the scope of this work. A tree-cotree splitting... more
The establishment of finite element based eigenanalysis as a numerical tool for the indepth understanding and revealing the characteristics of Terahertz and photonic structures, constitute the scope of this work. A tree-cotree splitting formulation method is used for the removal of imaginary and dc spurious modes. The Ritz vectors are appropriately restricted during the linearization technique of the polynomial eigenproblem. The capabilities of the method are demonstrated presenting certain microdisk and microrings whispering gallery modes eigenvalues and eigenvectors.
Recently we have proposed a finite element based eigenanalysis for lossy and unbounded structures. Our present effort aims at the validation of this technique for the study of complex radiating structures like the cavity backed type. The... more
Recently we have proposed a finite element based eigenanalysis for lossy and unbounded structures. Our present effort aims at the validation of this technique for the study of complex radiating structures like the cavity backed type. The typical Absorbing Boundary Condition (ABC) of 1st kind is employed, while finite conductivity is introduced at the metallic parts of the studied structure. The spurious modes are being suppressed by the enforcement of "divergence-free" constraint equations in the whole domain. It is proved in the current work that the non-physical modes restriction of the solution domain is achieved only by the projection of the seeding vector in the null space of the irrotational field, during the linearization procedure.
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ABSTRACT A study of reverberation chambers based on a three dimensional finite element eigenanalysis is elaborated. For this purpose the electric field vector wave equation is transformed into its weak form using the Galerkin procedure... more
ABSTRACT A study of reverberation chambers based on a three dimensional finite element eigenanalysis is elaborated. For this purpose the electric field vector wave equation is transformed into its weak form using the Galerkin procedure and discretized with the aid of tetrahedral edge elements. The resulting system of equations is then formulated into a generalized eigenproblem for a complex frequency (omega). When losses are ignored this eigenproblem is linear but is highly singular resulting to spurious solutions, a characteristic common to all numerical methods when analyzing lossless cavities. Including wall and material losses the singularity is reduced but the eigenproblem becomes nonlinear. Herein, the lossless case is considered first with an attempt to reject spurious solutions. Artificial air losses are then introduced to handle the singularity and the effects of these losses are checked against analytical solutions for a simple cavity. The rigorous non-linear eigenproblem including the realistic conducting walls and materials losses is currently under consideration.
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A review of our research effort on the eigenanalysis of open-radiating and closed, straight as well as curved, also including sections of periodic structures is presented herein. The elaborated geometries are arbitrary shaped and loaded... more
A review of our research effort on the eigenanalysis of open-radiating and closed, straight as well as curved, also including sections of periodic structures is presented herein. The elaborated geometries are arbitrary shaped and loaded in general with inhomogeneous and/or anisotropic media. Our previous work was focused on two dimensional (2-D) waveguiding structures and particularly on open-radiating waveguides including leaky
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A characteristic mode eigenanalysis exploiting Finite Element Methofi (FEM) features is introduced. In the typical characteristic mode eigenanalysis the Method of Moment (MoM) is utilized (llarringion R. F.. and Mautz J. R., IEEE Trans,... more
A characteristic mode eigenanalysis exploiting Finite Element Methofi (FEM) features is introduced. In the typical characteristic mode eigenanalysis the Method of Moment (MoM) is utilized (llarringion R. F.. and Mautz J. R., IEEE Trans, on Ant. and Propagat., AP-19, 1971). Moreover, to solve composite structures including both metallic as well as material-dielectric loading, a modified surface integral equation of MoM is demanded (Shafai, IEEE Trans, on Ant. and Propagat., 34, 666–673, 1986). Equivalent electric and magnetic currents are defined in order to take into consideration the interaction between the different homogeneous parts. However, it is proved thai the linear system that occurs, should be solved only in terms of the equivalent electric current that flows on the metallic parts, eliminating all the other currents from the final system (Maximidis R.T., Zekios C.L., Kaifas T.N., Vafiadis E.E. and Kvriacou, G.A., EuCAP 2014, 2822666–2826, 2014).
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A very powerfull tool first to device an appropriate geometry and then to design the related MIMO antenna is introduced based on the “characteristic modes” eigenanalysis. The ultimate task of this methodology refers to the formulation of... more
A very powerfull tool first to device an appropriate geometry and then to design the related MIMO antenna is introduced based on the “characteristic modes” eigenanalysis. The ultimate task of this methodology refers to the formulation of a mobile unit chassis into a multifunctional MIMO antenna. The numerical evaluation of the complex impedance matrix after its split into its real and imaginary part provides valuable physical insight of the structure. It is proved that a surface current density mode eigencurrent is at resonance when its associated eigenvalue is zero. Explicitly the smaller the magnitude of the eigenvalue is, the more efficiently the mode radiates when is excited. Moreover, the corresponding eigencurrent distribution defines the radiation characteristics including its radiation pattern and its polarization. Examining the eigencurrent distribution over the structure the appropriate excitation type and its location can be selected.
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Abstract In this work the authors propose a Butler Matrix (BM) based beamforming network (BFN) that feeds a linear antenna array. A BM 8× 8 is integrated with a specific Switching Network (SN) and a group of Switched-Line Phase Shifters... more
Abstract In this work the authors propose a Butler Matrix (BM) based beamforming network (BFN) that feeds a linear antenna array. A BM 8× 8 is integrated with a specific Switching Network (SN) and a group of Switched-Line Phase Shifters (SLPS), in order to properly ...
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Abstract In previous works the authors introduced the Neural Network (NN) Direction of Arrival (DoA) estimation method for a switched-beam DS-CDMA system. In this paper the method's performance has been significantly improved,... more
Abstract In previous works the authors introduced the Neural Network (NN) Direction of Arrival (DoA) estimation method for a switched-beam DS-CDMA system. In this paper the method's performance has been significantly improved, enabling its application not only to ...
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ABSTRACT
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Abstract A novel hybrid finite-element method for the analysis of leaky-waveguide structures is presented. The possibly radiating structure is enclosed within a fictitious circular contour-C in order to truncate the infinite solution... more
Abstract A novel hybrid finite-element method for the analysis of leaky-waveguide structures is presented. The possibly radiating structure is enclosed within a fictitious circular contour-C in order to truncate the infinite solution domain. The field in the unbounded domain, ...