| 1. |
- Capek, Miloslav, et al.
(författare)
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Numerical Benchmark based on characteristic modes of a spherical shell
- 2017
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Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings. - 9781538632840 ; 2017-January, s. 965-966
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Konferensbidrag (refereegranskat)abstract
- Characteristic modes of a spherical shell are found analytically and compared with numerical solutions acquired from both in-house and commercial packages. These studies led to a proposal of several independent benchmarks, all with analytically known results. Dependence on mesh size, electrical size and other parameters can easily be incorporated. It is observed that all contemporary implementations have limitations.
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| 2. |
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| 3. |
- Gustafsson, Mats, et al.
(författare)
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Antenna Current Optimization using MATLAB and CVX
- 2016
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Ingår i: FERMAT. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- Antenna current optimization is a tool that offers many possibilities in antenna technology. Optimal currents are determined in the antenna design region and used for physical understanding, as a priori estimates of the possibilities todesign antennas, physical bounds and as figures of merits for antenna designs. Antenna current optimization is particularly useful for small antennas and antennas that are constrained by their electrical size. The initial non-convex antenna design optimization problem is reformulated as a convex optimizationproblem expressed in the currents on the antenna. This convex optimization problem is solved efficiently at a computational cost comparable to a Method of Moments (MoM) solution of the same geometry. In this paper a tutorial description of antenna current optimization is presented. Stored energies and their relation to the impedance matrix in MoM is reviewed. The convex optimization problems are solved using MATLAB and CVX. MoM data isincluded together with MATLAB and CVX codes to optimize the antenna current for strip dipoles and planar rectangles. Codes and numerical results for maximization of the gain to Q-factor quotient and minimization of the Q-factor for prescribed radiated fields are provided.
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| 4. |
- Gustafsson, Mats, et al.
(författare)
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Physical Bounds of Antennas
- 2015
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Ingår i: Handbook of Antenna Technologies. - Singapore : Springer Singapore. - 9789814560757 ; , s. 1-32
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Bokkapitel (refereegranskat)abstract
- Design of small antennas is challenging because fundamental physics limits the antennas performance. Physical bounds provide basic restrictions on the antenna performance solely expressed in the available antenna design space. These bounds offer antenna designers a priori information about the feasibility of antenna designs and a figure of merit for different antenna designs. Here, an overview of physical bounds on antennas and the development from circumscribing spheres to arbitrary shaped regions and embedded antennas are presented. The underlying assumptions for the methods based on circuit models, mode expansions, forward scattering, and current optimization are illustrated and their pros and cons are discussed. The physical bounds are compared with numerical data for several antennas.
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| 5. |
- Gustafsson, Mats, et al.
(författare)
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Physical bounds of antennas
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Design of small antennas is challenging because fundamental physics limits the performance. Physical bounds provide basic restrictions on the antenna performance solely expressed in the available antenna design space. These limits offer antenna designers a-priori information about the feasibility of antenna designs and a figure of merit for different designs. Here, an overview of physical bounds on antennas and the development from circumscribing spheres to arbitrary shaped regions and embedded antennas are presented. The underlying assumptions for the methods based on circuit models, mode expansions, forward scattering, and current optimization are illustrated and their pros and cons are discussed. The physical bounds are compared with numerical data for several antennas.
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| 6. |
- Gustafsson, Mats, et al.
(författare)
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Q factors for antennas in dispersive media
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Stored energy and Q-factors are used to quantify the performance of small antennas. Accurate and efficient evaluation of the stored energy is also essential for current optimization and the associated physical bounds. Here, it is shown that the frequency derivative of the input impedance and the stored energy can be determined from the frequency derivative of the electric field integral equation. The expressions for the differentiated input impedance and stored energies differ by the use of a transpose and Hermitian transpose in the quadratic forms. The quadratic forms also provide simple single frequency formulas for the corresponding Q-factors. The expressions are further generalized to antennas integrated in temporally dispersive media. Numerical examples that compare the different Q-factors are presented for dipole and loop antennas in conductive, Debye, Lorentz, and Drude media. The computed Q-factors are also verified with the Q-factor obtained from the stored energy in Brune synthesized circuit models.
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| 7. |
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| 8. |
- Helander, Jakob, et al.
(författare)
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A Comparison of Macro Basis Function Methods for Interconnected Endfire Antenna Arrays
- 2017
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1536-1225. ; 16, s. 2159-2162
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Tidskriftsartikel (refereegranskat)abstract
- Two approaches to the macro basis function (MBF) method that target interconnected subdomains have been adapted to finite linear arrays, and benchmarked against each other in order to estimate their performance with respect to the strong near field coupling that occurs under the endfire mode operation. The methods, here referred to as methods A and B, are based on the synthetic function and characteristic basis function method, respectively, presented in the previous literature. The occurrence of very strong near-field coupling can be seen to affect the number of MBFs required for a certain level of accuracy, although both approaches perform well under the test scenario. However, method B provides a considerably more efficient compression with respect to a maximum acceptable error level.
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| 9. |
- Helander, Jakob, et al.
(författare)
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Multi-Port Element for Grating Lobe Suppression in Sparse VHF Phased Array Radars
- 2019
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 67:10, s. 6667-6671
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Tidskriftsartikel (refereegranskat)abstract
- A multi-port element approach, engineered to address practical design challenges of very high frequency (VHF) phased array radar systems, is presented in this communication. A cornerstone of the antenna element design is its simplicity, which counteracts the mobility issues of physically large and unavoidably bulky ground-based VHF radar systems. The multi-port element introduces a third dimension in the otherwise planar array configuration. Using a non-linear optimization scheme to realize a set of matching networks for the element, the active loading from surrounding elements in the array environment is suppressed resulting in a non-distorted embedded element pattern. The element is compared to the resembling Yagi-Uda design in terms of standard multi-port and radar metrics. Simulated results indicate that the element enables a significant suppression of grating lobes when beam steering within a limited angular sector, which in turn has an overall positive impact on the array performance.
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| 10. |
- Helander, Jakob, et al.
(författare)
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On the issue of simulating very large endfire arrays with complex antenna geometries
- 2016
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Ingår i: 2016 URSI International Symposium on Electromagnetic Theory, EMTS 2016. - 9781509025022 ; , s. 737-740
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Konferensbidrag (refereegranskat)abstract
- This paper discusses some of the main issues of efficient analysis of electrically very large endfire arrays, and further proposes approaches for developing flexible simulation tools for this particular purpose. Some initial results supporting the endfire array design issue are presented, as well as some preliminary examples of implemented compression- and acceleration methods.
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| 11. |
- Helander, Jakob, et al.
(författare)
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Synthesis of Large Endfire Antenna Arrays using Convex Optimization
- 2018
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 66:2, s. 712-720
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Tidskriftsartikel (refereegranskat)abstract
- An innovative approach utilizing convex optimization to simultaneously conduct pattern synthesis and improve the matching of large scale endfire antenna arrays is proposed in this paper. A fast full-wave analysis tool facilitates the computation of the necessary data for running the optimization routine, and enables analysis on arrays with dimensions 100λ × 6λ for the highest simulated frequency. Simulated results are provided for various array configurations of bowties, and the results show that improved matching can be obtained while maintaining a clear endfire far field pattern analogous to the pattern obtained with the classical Hansen-Woodyard excitation. The spatial dependence on the amplitude of the optimized input waves in the antenna ports indicate that a considerable fraction of the input power is fed to the antennas at the array’s front, in the direction of where the main lobe is launched.
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| 12. |
- Schab, Kurt, et al.
(författare)
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Energy Stored by Radiating Systems
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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 well as using demonstrative examples from electrostatics, circuits, and radiating systems. Along the way, the concept of unobservable energy is introduced to formalize such challenges. Existing methods of defining stored energy in radiating systems are then reviewed in a framework based on technical commonalities rather than chronological order. Equivalences between some methods under common assumptions are highlighted, along with the strengths, weaknesses, and unique applications of certain techniques. Numerical examples are provided to compare the relative margin between methods on several radiating structures.
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| 13. |
- Schab, Kurt, et al.
(författare)
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Energy Stored by Radiating Systems
- 2018
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Ingår i: IEEE Access. - 2169-3536. ; 6, s. 10553-10568
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Tidskriftsartikel (refereegranskat)abstract
- 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 well as using demonstrative examples from electrostatics, circuits, and radiating systems. Along the way, the concept of unobservable energy is introduced to formalize such challenges. Existing methods of defining stored energy in radiating systems are then reviewed in a framework based on technical commonalities rather than chronological order. Equivalences between some methods under common assumptions are highlighted, along with the strengths, weaknesses, and unique applications of certain techniques. Numerical examples are provided to compare the relative margin between methods on several radiating structures.
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| 14. |
- Tayli, Doruk, et al.
(författare)
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Accurate and Efficient Evaluation of Characteristic Modes
- 2018
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 66:12, s. 7066-7075
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Tidskriftsartikel (refereegranskat)abstract
- A new method to improve the accuracy and efficiency of characteristic mode (CM) 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 (MoM) solution of the electric field integral equation (EFIE) to factorize the real part of the impedance matrix. The factorization is then employed in the computation of CMs, which improves the accuracy as well as the computational speed. An additional benefit is a rapid computation of far fields. The method can easily be integrated into existing MoM solvers. Several structures are investigated illustrating the improved accuracy and performance of the new method.
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| 15. |
- Tayli, Doruk, et al.
(författare)
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Accurate and Efficient Evaluation of Characteristic Modes
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A new method to improve the accuracy and efficiency of CM 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 MoM solution of the EFIE to factorize the real part of the impedance matrix. The factorization is then employed in the computation of CM, which improves the accuracy as well as the computational speed. An additional benefit is a rapid computation of far fields. The method can easily be integrated into existing MoM solvers. Several structures are investigated illustrating the improved accuracy and performance of the new method.
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| 16. |
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| 17. |
- Tayli, Doruk, et al.
(författare)
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Calculating the Physical Bounds for Antennas Above a Ground Plane
- 2014
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Ingår i: 2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS). - 9781467352253
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Konferensbidrag (refereegranskat)abstract
- The physical bounds for antennas above a ground plane is analyzed in this paper. Optimal antenna G/Q ratio and Q factor are calculated using convex optimization from stored electric and magnetic energy matrices, obtained from a method of moments solver. Physical bounds for a patch antenna with different heights above a ground plane are investigated. Results are verified using commercially available electromagnetic solver FEKO.
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| 18. |
- Tayli, Doruk
(författare)
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Computational Tools for Antenna Analysis and Design
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many engineers and scientists prevalently use computational tools in electromagnetics, which is also the predominant case for antennas. The ever-increasing number of applications and technologies that employ antennas create a constant demand to improve and extend existing tools and develop new ones. This dissertation investigates computational tools for antenna analysis and design. Antenna current optimization is used to determine the theoretical performance bounds on antennas above a ground plane. The results add insight to the performance of patch antennas and can thereby benefit antenna designers. Moreover, the limits are used to design antennas in method of moments (MoM) and genetic algorithm (GA) solvers. The matrices used to compute characteristic modes, that is a generalized eigenvalue problem, are analyzed. Numerical issues of the calculation are circumvented, and the computational complexity is decreased with the use of spherical vector waves. A macro basis function (MBF) and adaptive cross approximation (ACA) algorithm framework is employed to simulate vast endfire arrays. Convex optimization is used to synthesize endfire patterns with improved matching performance. Furthermore, the performance of two techniques that are used in the MBF method to model interconnected arrays is investigated in the endfire mode.
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| 19. |
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| 20. |
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| 21. |
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| 22. |
- Tayli, Doruk, et al.
(författare)
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Physical Bounds for Antennas Above a Ground Plane
- 2016
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1548-5757. ; 15, s. 1281-1284
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Tidskriftsartikel (refereegranskat)abstract
- Physical limitations of antennas above infinite perfect electric conductor (PEC) ground planes are determined using the stored electromagnetic energy. Stored energies are computed with the method of moments (MoM) and the image theory. Convex optimization is used to derive the G/Q ratio and Q-factor for a reference geometry and the results are compared for different antenna types.
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| 23. |
- Tayli, Doruk, et al.
(författare)
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Physical Bounds for Antennas Above a Ground Plane
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Physical limitations of antennas above infinite perfect electric conductor (PEC) ground planes are determined using the stored electromagnetic energy. Stored energies are computed with the method of moments (MoM) and the image theory. Convex optimization is used to derive the G/Q ratio and Q-factor for a reference geometry and the results are compared for different antenna types.
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| 24. |
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