Miloslav Čapek

Miloslav Čapek
Czech Technical University in Prague | ČVUT · Department of Electromagnetic Field

Associate Professor

About

115
Publications
17,928
Reads
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924
Citations
Introduction
Miloslav Capek was awarded his B.Sc. degree (2007), his M.Sc. degree (2009), and his Ph.D. degree (2014) in electrical engineering from the Czech Technical University (CTU), Prague, Czech Republic. In 2017 he was appointed Associate Professor at the Department of Electromagnetic Field at the CTU in Prague, where he set up a new course on Matlab, which is now offered in each semester. During his doctoral studies, Miloslav created the basis of the AToM (Antenna Toolbox for Matlab) package, and he now leads its the development. Miloslav is a member of the IEEE and the Radioengineering Society, a EurAAP delegate, and an Associate Editor of Radioengineering. He has been a grant holder and member of a research team for several national and international projects.
Additional affiliations
February 2014 - present
Czech Technical University in Prague
Position
  • Undergraduate subject on Introduction to MATLAB programming
Description
  • New course on CTU-FEE from 2014.
September 2010 - June 2013
Czech Technical University in Prague
Position
  • Research Assistant
January 2010 - June 2013
Czech Technical University in Prague
Position
  • Computational seminars in electromagnetic field theory
Education
September 2009 - June 2014
Czech Technical University in Prague
Field of study
  • Radioelectronics
September 2007 - June 2009
Czech Technical University in Prague
Field of study
  • Telecommunication

Publications

Publications (115)
Preprint
Full-text available
Characteristic modes are formulated using the scattering dyadic, which maps incident plane waves to scattered far fields generated by an object of arbitrary material composition. Numerical construction of the scattering dyadic using arbitrary full-wave electromagnetic solvers is demonstrated in examples involving a variety of dielectric and magneti...
Article
Nearly all practical applications of the theory of characteristic modes (CMs) involve the use of computational tools. This article is the second in a series of five on CM [1]-[4]. Here, we review the general transformations that move CMs from a continuous theoretical framework to a discrete representation compatible with numerical methods. We also...
Article
Over the past decade, characteristic mode analysis (CMA) research has grown from a niche topic to a mainstream topic, warranting a tutorial-style special issue to survey the significant progress that has been made in this field. In this introductory article, the focus is on providing the big picture. We start with a simple description of characteri...
Article
Hybrid computational schemes combining the advantages of a method of moments formulation of a field integral equation and T-matrix method are developed in this paper. The hybrid methods are particularly efficient when describing the interaction of electrically small complex objects and electrically large objects of canonical shapes such as spherica...
Preprint
Full-text available
Memetics for shape synthesis, introduced in Part 1, is examined on antenna design examples. It combines local and global techniques to accelerate convergence and to maintain robustness. Method-of-moments matrices are used to evaluate objective functions. By applying the Shermann-Morrison-Woodbury identity, the repetitively performed structural upda...
Preprint
Fundamental bounds on quadratic electromagnetic metrics are formulated and solved via convex optimization. Both dual formulation and method-of-moments formulation of the electric field integral equation are used as key ingredients. The trade-off between metrics is formulated as a multi-objective optimization resulting in Pareto-optimal sets. Substr...
Preprint
Full-text available
A novel inverse design framework over a fixed discretization grid using method of moments for the shape optimization of radiation devices is proposed. The formulation is discrete and solves the original combinatorial problem. Fixed discretization provides an inversion-free, exact-reanalysis-based evaluation of the smallest topology perturbations. T...
Preprint
Full-text available
This is the second component of a two-part paper dealing with a unification of characteristic mode decomposition. This second part addresses modal tracking and losses and presents several numerical examples for both surface- and volume-based method-of-moment formulations. A new tracking algorithm based on algebraic properties of the transition matr...
Article
A technique for designing antenna excitation realizing orthogonal states is presented. It is shown that a symmetric antenna geometry is required in order to achieve orthogonality with respect to all physical quantities. A maximal number of achievable orthogonal states and a minimal number of ports required to excite them are rigorously determined f...
Preprint
Full-text available
A unification of characteristic mode decomposition for all method-of-moment formulations of field integral equations describing free-space scattering is derived. The work is based on an algebraic link between impedance and transition matrices, the latter of which was used in early definitions of characteristic modes and is uniquely defined for all...
Preprint
Full-text available
Nearly all practical applications of the theory of characteristic modes (CMs) involve the use of computational tools. Here in Paper 2 of this Series on CMs, we review the general transformations that move CMs from a continuous theoretical framework to a discrete representation compatible with numerical methods. We also review several key topics rel...
Article
Fundamental bounds on the performance of monochromatic scattering-cancellation and field-zeroing cloaks made of prescribed linear passive materials occupying a predefined design region are formulated by projecting field quantities onto a sub-sectional basis and applying quadratically constrained quadratic programming. Formulations are numerically t...
Article
The optimal spectral efficiency and number of independent channels for MIMO antennas in isotropic multipath channels are investigated when bandwidth requirements are placed on the antenna. By posing the problem as a convex optimization problem restricted by the port Q-factor a semi-analytical expression is formed for its solution. The antennas are...
Article
A problem of the erroneous duality gap caused by the presence of symmetries is solved in this paper utilizing point group theory. The optimization problems are first divided into two classes based on their predisposition to suffer from this deficiency. Then, the classical problem of Q-factor minimization is shown in an example where the erroneous d...
Preprint
Full-text available
Fundamental bounds on the performance of monochromatic scattering-cancellation and field-zeroing cloaks made of prescribed linear passive materials occupying a predefined design region are formulated by projecting field quantities onto a sub-sectional basis and applying quadratically constrained quadratic programming. Formulations are numerically t...
Preprint
Full-text available
Hybrid computational schemes combining the advantages of a method of moments formulation of a field integral equation and T-matrix method are developed in this paper. The hybrid methods are particularly efficient when describing the interaction of electrically small complex objects and electrically large objects of canonical shapes such as, spheric...
Article
Trade-offs between absorption and scattering cross sections of lossy obstacles confined to an arbitrarily shaped volume are formulated as a multi-objective optimization problem solvable by Lagrangian-dual methods. Solutions to this optimization problem yield a Pareto-optimal set, the shape of which reveals the feasibility of achieving simultaneousl...
Article
A numerically effective description of the total active reflection coefficient and realized gain are studied for multi-port antennas. Material losses are fully considered. The description is based on operators represented in an entire-domain port-mode basis, i.e., on matrices with favorably small dimensions. Optimal performance is investigated and...
Preprint
Full-text available
Trade-offs between feasible absorption and scattering cross sections of obstacles confined to an arbitrarily shaped volume are formulated as a multi-objective optimization problem solvable by Lagrangian-dual methods. Solutions to this optimization problem yield a Pareto-optimal set, the shape of which reveals the feasibility of achieving simultaneo...
Article
Full-text available
A single‐ and multi‐objective optimization package is presented and described in detail. It contains an ensemble of local and global optimization routines. Procedures controlling variable number of dimensions are implemented as well, which is a rare feature among optimization oriented packages. The package is provided as a MATLAB toolbox. It excels...
Article
Full-text available
A general framework for determining fundamental bounds in nanophotonics is introduced in this paper. The theory is based on convex optimization of dual problems constructed from operators generated by electromagnetic integral equations. The optimized variable is a contrast current defined within a prescribed region of a given material constitutive...
Preprint
Full-text available
A problem of the erroneous duality gap caused by the presence of symmetries is solved in this paper utilizing point group theory. The optimization problems are first divided into two classes based on their predisposition to suffer from this deficiency. Then, the classical problem of Q-factor minimization is shown in an example where the erroneous d...
Cover Page
Course on Characteristic Modes: Theory and Applications Aimed at postgraduate research students and industrial engineers who want to acquire deep insight into the theory and applications of characteristic modes.
Preprint
A technique of designing antenna excitation realizing orthogonal free-space channels is presented. It is shown that a symmetric antenna geometry is required in order to achieve orthogonality with respect to all physical quantities. A maximal number of reachable uncorrelated channels and a minimal number of feeders required to excite them are rigoro...
Preprint
Full-text available
The total active reflection coefficient and realized gain are studied for multi-port antennas. Material losses are fully considered. The full-wave solution to current density on an antenna body is utilized and bind together with connected transmission lines and matching circuits. The description is based on matrix operators represented in an entire...
Preprint
Full-text available
A general framework for determining fundamental bounds in nanophotonics is introduced in this paper. The theory is based on convex optimization of dual problems constructed from operators generated by electromagnetic integral equations. The optimized variable is a contrast current defined within a prescribed region of a given material constitutive...
Article
Full-text available
Issues in modal tracking in the presence of crossings and crossing avoidances between eigenvalue traces are solved via the theory of point groups. The von Neumann-Wigner theorem is used as a key factor in predictively determining mode behavior over arbitrary frequency ranges. The implementation and capabilities of the proposed procedure are demonst...
Article
Considerable time is often spent optimizing antennas to meet specific design metrics. Rarely, however, are the resulting antenna designs compared to rigorous physical bounds on those metrics. Here, we study the performance of optimized planar meander line antennas with respect to such bounds. Results show that these simple structures meet the lower...
Article
Fundamental bounds on antenna gain are found via convex optimization of the current density in a prescribed region. Various constraints are considered, including self-resonance and only partial control of the current distribution. Derived formulas are valid for arbitrarily shaped radiators of a given conductivity. All the optimization tasks are red...
Preprint
Full-text available
The optimal spectral efficiency of MIMO antennas in an ideal line-of-sight channel is investigated when bandwidth requirements are placed on the antenna. By posing the problem as a convex optimization problem restricted by the stored energy a semi-analytical expression is formed for its solution. It is shown that this solution is solely dependent o...
Article
Full-text available
A recently introduced technique of topology sensitivity in method of moments is extended by the possibility of adding degrees-of-freedom (reconstruct) into underlying structure. The algebraic formulation is inversion-free, suitable for parallelization and scales favorably with the number of unknowns. The reconstruction completes the nearest neighbo...
Article
A method evaluating the sensitivity of a given parameter to topological changes is proposed within the method of moments paradigm. The basis functions are used as degrees of freedom which, when compared to the classical pixeling technique, provide important advantages, one of them being impedance matrix inversion free evaluation of the sensitivity....
Preprint
Full-text available
A recently introduced technique of topology sensitivity in method of moments is extended by the possibility of adding degrees-of-freedom (reconstruct) into underlying structure. The algebraic formulation is inversion-free, suitable for parallelization and scales favorably with the number of unknowns. The reconstruction completes the nearest neighbo...
Preprint
Full-text available
Fundamental bounds on antenna gain are found via convex optimization of the current density in a prescribed region. Various constraints are considered, including self-resonance and only partial control of the current distribution. Derived formulas are valid for arbitrarily shaped radiators of a given conductivity. All the optimization tasks are red...
Preprint
Full-text available
Modal tracking in the presence of crossings and crossing avoidances between eigenvalue traces is solved via the theory of point groups. The von Neumann-Wigner theorem is used as a key factor in predictively determining mode behavior over a frequency range. The capabilities of the proposed procedure are demonstrated on a particular case of character...
Preprint
Full-text available
Considerable time is often spent optimizing antennas to meet specific design metrics. Rarely, however, are the resulting antenna designs compared to rigorous physical bounds on those metrics. Here we study the performance of optimized planar meander line antennas with respect to such bounds. Results show that these simple structures meet the lower...
Preprint
Full-text available
A method evaluating the sensitivity of a given parameter to topological changes is proposed within the method of moments paradigm. The basis functions are used as degrees of freedom which, when compared to the classical pixeling technique, provide important advantages, one of them being impedance matrix inversion free evaluation of the sensitivity....
Article
Full-text available
Radiation efficiencies of modal current densities distributed on a spherical shell are evaluated in terms of dissipation factor. The presented approach is rigorous, yet simple and straightforward, leading to closed-form expressions. The same approach is utilized for a two-layered shell and the results are compared with other models existing in the...
Article
Full-text available
Existing optimization methods are used to calculate the upper-bounds on radiation efficiency with and without the constraint of self-resonance. These bounds are used for the design and assessment of small electric-dipole-type antennas. We demonstrate that the assumption of lossless, lumped, external tuning skews the true nature of radiation efficie...
Article
Full-text available
The trade-off between radiation efficiency and antenna bandwidth, expressed in terms of Q-factor, for small antennas is formulated as a multi-objective optimization problem in current distributions of predefined support. Variants on the problem are constructed to demonstrate the consequences of requiring a self-resonant current as opposed to one tu...
Article
The purpose of this comment is twofold. First, it shows that formulas for dissipation factors from the commented paper are not fully correct. Second, it shows that the results presented in the commented paper can alternatively be obtained by directly manipulating spherical vector waves leading to simple formulas which are valid for any electrical s...
Article
Full-text available
A new method to improve the accuracy of characteristic modes decomposition for perfectly conducting bodies is presented. The method uses the expansion of the Green dyadic in spherical vector waves. This expansion is utilized in the method of moments solution of the electric field integral equation to improve the numerical range of the real part of...
Article
Full-text available
Though commonly used to calculate Q-factor and fractional bandwidth, the energy stored by radiating systems (antennas) is a subtle and challenging concept that has perplexed researchers for over half a century. Here, the obstacles in defining and calculating stored energy in general electromagnetic systems are presented from first principles as wel...
Article
Full-text available
Characteristic modes of a spherical shell are found analytically as spherical harmonics normalized to radiate unitary power and to fulfill specific boundary conditions. The presented closed-form formulas lead to a proposal of precise synthetic benchmarks which can be utilized to validate the method of moments matrix or performance of characteristic...
Article
Full-text available
Ambiguities in the definition of stored energy within distributed or radiating electromagnetic systems motivate the discussion of the well-defined concept of recoverable energy. This concept is commonly overlooked by the community and the purpose of this communication is to recall its existence and to discuss its relationship to fractional bandwidt...
Article
The optimal currents on arbitrarily shaped radiators with respect to the minimum quality factor Q are found using a simple and efficient procedure. The solution starts with a reformulation of the problem of minimizing quality factor Q as an alternative, so-called dual, problem. Taking advantage of modal decomposition and group theory, it is shown t...
Article
Full-text available
Aspects of the theory of characteristic modes, based on their variational formulation, are presented and an explicit form of a related functional, involving only currents in a spatial domain, is derived. The new formulation leads to deeper insight into the modal behavior of radiating structures as demonstrated by a detailed analysis of three canoni...
Article
A full-wave numerical scheme of polarisability tensors evaluation is presented. The method accepts highly conducting bodies of arbitrary shape and explicitly accounts for the radiation as well as ohmic losses. The method is verified on canonical bodies with known polarisability tensors, such as a sphere and a cube, as well as on realistic scatterer...
Conference Paper
An optimization scheme yielding a current density in a given spatial region exhibiting the lowest tuned radiation quality factor is presented. Rather than assuming an external tuning by a lumped element, the current density is constrained to be self-resonant. The solution is presented as a weighted sum of characteristic modes and some important rem...
Conference Paper
This work describes an efficient and powerful technique to obtain optimal currents with respect to the lower bounds of quality factor Q for an arbitrarily shaped electrically small antenna made of perfect conductor. The resulting optimal currents are expressed in terms of characteristic mode basis with the minimum always being obtained by either on...
Article
Full-text available
Antenna parameters particularly relevant to electrically small antenna design are reviewed in this paper. Source current definitions are accentuated leading to the introduction of the source concept which advantageously utilize only spatially bounded quantities. The framework of the source concept incorporates powerful techniques such as structural...
Article
Full-text available
This paper deals with the old yet unsolved problem of defining and evaluating the stored electromagnetic energy-a quantity essential for calculating the quality factor, which reflects the intrinsic bandwidth of the considered electromagnetic system. A novel paradigm is proposed to determine the stored energy in the time domain leading to the method...