| 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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