| 1. |
- Capek, Miloslav, et al.
(författare)
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Characteristic Mode Decomposition of Scattering Dyadic
- 2022
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Ingår i: 2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, AP-S/URSI 2022 - Proceedings. - 9781665496582 ; , s. 283-284
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Konferensbidrag (refereegranskat)abstract
- This abstract describes the decomposition of a matrix representing a scattering dyadic into characteristic modes. Scattering dyadic, as compared to conventionally used impedance matrices, are independent of numerical method used to compute them and the same characteristic mode formulation can be used for decomposition of composite and inhomogeneous materials. The utilization of scattering dyadic makes it possible to synthesize characteristic modes which are orthogonal over prescribed portions of the far-field sphere, or ex-post decomposition of measured data. The theory is demonstrated on a simple example and its features are discussed.
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| 2. |
- Capek, Miloslav, et al.
(författare)
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Characteristic Mode Decomposition Using the Scattering Dyadic in Arbitrary Full-Wave Solvers
- 2023
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:1, s. 830-839
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Tidskriftsartikel (refereegranskat)abstract
- 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 magnetic materials. Wrapper functions for computing characteristic modes in method-of-moments, finite-difference time domain, and finite element solvers are provided as supplementary material.
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| 3. |
- Capek, Miloslav, et al.
(författare)
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Cloaking Synthesis Based on Exact Re-analysis
- 2022
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Ingår i: 2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, AP-S/URSI 2022 - Proceedings. - 9781665496582 ; , s. 293-294
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Konferensbidrag (refereegranskat)abstract
- A novel synthesizing procedure is introduced and employed to extract locally-optimal cloaking devices. Their performance is compared with fundamental bounds found using a convex optimization approach. The optimization method is based on a method-of-moments paradigm utilizing rank-1 updates of the structure iteratively performed based on a greedy algorithm. This approach produces locally optimal shapes and its incorporation into a global search strategy is described and applied. As compared to classical topology optimization schemes, no post-processing is required. Two canonical problems are solved and presented.
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| 4. |
- Capek, Miloslav, et al.
(författare)
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Fundamental Bounds for Volumetric Structures and Their Feasibility
- 2020
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Ingår i: 14th European Conference on Antennas and Propagation, EuCAP 2020. - 9788831299008
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Konferensbidrag (refereegranskat)abstract
- Fundamental bounds on antenna and scattering metrics are presented in this paper utilizing volumetric method of moments. This makes it possible to investigate scenarios not solvable with classical surface method of moments which assumes that good conductors as used. One practical example is the study of plasmonic devices whose operation relies on the interaction between material properties and radiation mechanisms. The implementation of the code is briefly summarized, including some implementation hints which allow for fast evaluation of necessary matrix operators. Two optimization problems are introduced and solved for scattering and antenna problems. Feasibility of the bounds will be investigated with topology optimization and the results will be presented during the conference.
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| 5. |
- Capek, Miloslav, et al.
(författare)
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Minimization of Antenna Quality Factor
- 2017
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 65:8, s. 4115-4123
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Tidskriftsartikel (refereegranskat)abstract
- Optimal currents on arbitrarily shaped radiators with respect to the minimum quality factor 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 that the dual problem can easily be solved and always results in minimal quality factor Q. Moreover, the optimization procedure is generalized to minimize quality factor Q for embedded antennas, with respect to the arbitrarily weighted radiation patterns, or with prescribed magnitude of the electric and magnetic near-fields. The obtained numerical results are compatible with previous results based on composition of modal currents, convex optimization, and quasistatic approximations; however, using the methodology in this paper, the class of solvable problems is significantly extended.
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| 6. |
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| 7. |
- Capek, Miloslav, et al.
(författare)
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Optimal Planar Electric Dipole Antennas Searching for antennas reaching the fundamental bounds on selected metrics.
- 2019
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Ingår i: IEEE Antennas & Propagation Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 1045-9243 .- 1558-4143. ; 61:4, s. 19-29
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Tidskriftsartikel (refereegranskat)abstract
- 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 bound on the radiation quality factor (Q-factor) (maximizing single-resonance fractional bandwidth) but are far from reaching the associated physical bounds for efficiency. The relative performance of other canonical antenna designs is comparable in similar ways, and the quantitative results are connected to intuitions from small antenna design, physical bounds, and matching network design.
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| 8. |
- Capek, Miloslav, et al.
(författare)
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Unified Approach to Characteristic Modes
- 2021
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Ingår i: 2021 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting : APS/URSI 2021 - Proceedings - APS/URSI 2021 - Proceedings. - 9781728146706 ; , s. 893-894
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Konferensbidrag (refereegranskat)abstract
- An algebraic link between transition matrix and impedance matrix is utilized in this work to unify characteristic mode decomposition originally proposed by Garbacz with a framework proposed later on by Harrington and Mautz. The resulting formulation is unique to all method of moments formulations, valid for all linear and lossless materials, and has many favorable properties. The unified prescription is applicable to surface equivalence, body-of-revolution, or volumetric method of moments formulations. The unification paves a way to establish characteristic modes as a standalone technique in time-harmonic domain being independent of method of moment paradigm, i.e., to utilize - for example - finite element method instead.
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| 9. |
- Chen, Yikai, et al.
(författare)
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Benchmark problem definition and cross-validation for characteristic mode solvers
- 2018
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Ingår i: European Conference on Antennas and Propagation (EuCAP), 2018.. - : Institution of Engineering and Technology. - 9781785618161
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Konferensbidrag (refereegranskat)abstract
- In October 2016, the Special Interest Group on Theory of Characteristic Modes (TCM) initiated a coordinated effort to perform benchmarking work for characteristic mode (CM) analysis. The primary purpose is to help improve the reliability and capability of existing CM solvers and to provide the means for validating future tools. Significant progress has already been made in this joint activity. In particular, this paper describes several benchmark problems that were defined and analyzes some results from the cross-validations of different CM solvers using these problems. The results show that despite differences in the implementation details, good agreement is observed in the calculated eigenvalues and eigencurrents across the solvers. Finally, it is concluded that future work should focus on understanding the impact of common parameters and output settings to further reduce variability in the results.
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| 10. |
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