The present work aims at an eigenanalysis methodology for lossy or open periodic structures incor... 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.
2018 7th International Conference on Modern Circuits and Systems Technologies (MOCAST)
The Characteristic Mode analysis of a drop-like supershaped patch antenna constitutes the main sc... 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.
2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting, 2020
As fifth generation (5G) wireless communication systems roll out, significant challenges exist to... 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.
2019 International Workshop on Antenna Technology (iWAT), 2019
The current work focuses on the study of tunable THz open structures, establishing an eigenmode a... 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.
2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting, 2020
In this paper a phased array consisting of eight tightly coupled parallel dipoles is studied. The... 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.
2017 International Workshop on Antenna Technology: Small Antennas, Innovative Structures, and Applications (iWAT), 2017
Eigenanalysis of canonically shaped structures served as an indispensable tool the conception and... 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.
2017 IEEE MTT-S International Microwave Symposium (IMS), 2017
The establishment of a rigorous full-wave eigenanalysis based on finite element method as numeric... 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.
2015 9th European Conference on Antennas and Propagation (EuCAP), 2015
A three dimensional Mode Matching/Collocation technique is proposed in the current work for the a... 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 ...
In this work, we present a rigorous full-wave eigenanalysis for the study of nanoantennas operati... 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...
A procedure for calculating the characteristic modes series and parallel resonances calculation b... 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.
A two dimensional Finite Difference Frequency Domain (2D-FDFD) eigenanalysis of an array consisti... 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.
It is of critical importance to efficiently and accurately evaluate both the internal and externa... 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.
The current work is the theoretical framework of the Research Project “Thales” entitled: “Develop... 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.
IEEE Transactions on Microwave Theory and Techniques, 2015
A generalization of the tree-cotree technique for the removal of imaginary and dc spurious modes ... 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.
The present work aims at an eigenanalysis methodology for lossy or open periodic structures incor... 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.
2018 7th International Conference on Modern Circuits and Systems Technologies (MOCAST)
The Characteristic Mode analysis of a drop-like supershaped patch antenna constitutes the main sc... 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.
2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting, 2020
As fifth generation (5G) wireless communication systems roll out, significant challenges exist to... 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.
2019 International Workshop on Antenna Technology (iWAT), 2019
The current work focuses on the study of tunable THz open structures, establishing an eigenmode a... 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.
2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting, 2020
In this paper a phased array consisting of eight tightly coupled parallel dipoles is studied. The... 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.
2017 International Workshop on Antenna Technology: Small Antennas, Innovative Structures, and Applications (iWAT), 2017
Eigenanalysis of canonically shaped structures served as an indispensable tool the conception and... 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.
2017 IEEE MTT-S International Microwave Symposium (IMS), 2017
The establishment of a rigorous full-wave eigenanalysis based on finite element method as numeric... 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.
2015 9th European Conference on Antennas and Propagation (EuCAP), 2015
A three dimensional Mode Matching/Collocation technique is proposed in the current work for the a... 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 ...
In this work, we present a rigorous full-wave eigenanalysis for the study of nanoantennas operati... 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...
A procedure for calculating the characteristic modes series and parallel resonances calculation b... 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.
A two dimensional Finite Difference Frequency Domain (2D-FDFD) eigenanalysis of an array consisti... 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.
It is of critical importance to efficiently and accurately evaluate both the internal and externa... 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.
The current work is the theoretical framework of the Research Project “Thales” entitled: “Develop... 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.
IEEE Transactions on Microwave Theory and Techniques, 2015
A generalization of the tree-cotree technique for the removal of imaginary and dc spurious modes ... 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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