| 1. |
- Capek, Miloslav, et al.
(author)
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Optimal Planar Electric Dipole Antennas Searching for antennas reaching the fundamental bounds on selected metrics.
- 2019
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In: IEEE Antennas & Propagation Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 1045-9243 .- 1558-4143. ; 61:4, s. 19-29
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Journal article (peer-reviewed)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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| 2. |
- Ehrenborg, Casimir, et al.
(author)
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Bandwidth-Constrained Capacity Bounds on MIMO Antennas
- 2019
-
Reports (other academic/artistic)abstract
- The optimal spectral efficiency of MIMO antennas in Rayleigh and ideal 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 simulated by method of moments and the solution is formulated both for structures fed by discrete ports, as well as for design regions characterized by an equivalent current. It is shown that this solution is solely dependent on the so-called energy modes of the antenna.These modes are compared to the characteristic modes and how to effectively excite them is investigated for a linear dipole array as well as a plate with embedded, and raised, antenna regions. The performance is illustrated through spectral efficiency over the Q-factor, a quantity that is connected to the true capacity. It is demonstrated that the Q-factor and the spectral efficiency form a Pareto trade-off bound, and that a certain Q-factor is Pareto optimal.
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| 3. |
- Ehrenborg, Casimir, et al.
(author)
-
Capacity Bounds and Degrees of Freedom for MIMO Antennas
- 2021
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In: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 69:9, s. 5388-5400
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Journal article (peer-reviewed)abstract
- 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 simulated by method of moments and the solution is formulated both for structures fed by discrete ports, as well as for design regions characterized by an equivalent current. It is shown that the solution is solely dependent on the eigenvalues of the so-called energy modes of the antenna. The magnitude of these eigenvalues is analyzed for a linear dipole array as well as a plate with embedded antenna regions. The energy modes are also compared to the characteristic modes to validate characteristic modes as a design strategy for MIMO antennas. The antenna performance is illustrated through spectral efficiency over the Q-factor, a quantity that is connected to the capacity. It is proposed that the number of energy modes below a given Q-factor can be used to estimate the degrees of freedom for that Q-factor.
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| 4. |
- Ehrenborg, Casimir, et al.
(author)
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Fundamental bounds on MIMO antennas
- 2018
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In: IEEE Antennas and Wireless Propagation Letters. - 1536-1225. ; 17:1, s. 21-24
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Journal article (peer-reviewed)abstract
- Antenna current optimization is often used to analyze the optimal performance of antennas. Antenna performance can be quantified in e.g., minimum Q-factor and radiation efficiency. The performance of MIMO antennas is more involved and, in general, a single parameter is not sufficient to quantify it. Here, the capacity of an idealized channel is used as the main performance quantity. An optimization problem in the current distribution for optimal capacity, measured in spectral efficiency, given a fixed Q-factor and radiation efficiency is formulated as a semi-definite optimization problem. A model order reduction based on characteristic and energy modes is employed to improve the computational efficiency. The performance bound is illustrated by solving the optimization problem numerically for rectangular plates and spherical shells.
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| 5. |
- Ehrenborg, Casimir, et al.
(author)
-
Fundamental bounds on MIMO antennas
- 2017
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Reports (other academic/artistic)abstract
- Antenna current optimization is often used to analyze the optimal perfor-mance of antennas. Antenna performance can be quantied in e.g., minimumQ-factor and maximal gain over Q-factor ratio. The performance of MIMOantennas is more involved and a single parameter is, in general, not sucientto quantify it. Here, the capacity of an idealized channel is used as the mainperformance quantity. An optimization problem in the current distributionfor optimal capacity, measured in spectral eciency, given a xed Q-factorand eciency is formulated as a semi-denite optimization problem. A modelorder reduction based on characteristic and energy modes is employed to im-prove the computational eciency. The bound is illustrated by solving theoptimization problem numerically for a rectangular plate.
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| 6. |
- Ehrenborg, Casimir, et al.
(author)
-
Physical bounds and automatic design of antennas above ground planes
- 2016
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In: 2016 URSI International Symposium on Electromagnetic Theory, EMTS 2016. - 9781509025022 ; , s. 233-235
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Conference paper (peer-reviewed)abstract
- Physical bounds for antennas above ground planes are calculated by optimizing the antenna current. The bounds are compared with antennas modeled as fragmented patches and optimized using genetic algorithms. Monopole structures over ground planes are modeled with image theory and optimized. The monopole over ground plane structure simplifies experimental verification of the bounds.
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| 7. |
- Ehrenborg, Casimir, et al.
(author)
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Physical bounds and radiation modes for MIMO antennas
- 2018
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Reports (other academic/artistic)abstract
- Modern antenna design for communication systems revolves around two extremes: devices, where only a small region is dedicated to antenna design, and base stations, where design space is not shared with other components. Both imply different restrictions on what performance is realizable. In this paper properties of both ends of the spectrum in terms of MIMO performance is investigated. For small antennas the size restriction dominates the performance parameters. The regions dedicated to antenna design induce currents on the rest of the device. Here a method for studying fundamental bound on spectral efficiency of such configurations is presented. For larger structures the number of degrees of freedom available per unit area is investigated for different shapes. Both of these are achieved by formulating a convex optimization problem for maximum spectral efficiency in the current density on the antenna. A closed form solution for this problem is formulated and investigated in relation to constraining parameters, such as size and efficiency.
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| 8. |
- Ehrenborg, Casimir, et al.
(author)
-
Physical bounds and radiation modes for MIMO antennas
- 2020
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In: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 68:6, s. 4302-4311
-
Journal article (peer-reviewed)abstract
- Modern antenna design for communication systems revolves around two extremes: devices, where only a small region is dedicated to antenna design, and base stations, where design space is not shared with other components. Both imply different restrictions on what performance is realizable. In this paper a computationally efficient method for calculating the fundamental performance bound on spectral efficiency is presented. The performance bound is calculated for MIMO antennas with a radiation efficiency requirement. A convex optimization problem is formulated in the current density of the antenna, this problem is solved by constructing its dual problem. The solution to this problem is based on a set of modes known as the radiation modes. This paper shows how to perform modal analysis using these modes to evaluate design strategies for maximal spectral efficiency. This is illustrated both for electrically small, and large, structures. For electrically small structures, sub regions for antenna design are evaluated and analyzed. These are compared to N-degree MIMO systems. For electrically large structures the degrees of freedom per unit area of different shapes are analyzed using radiation modes.
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| 9. |
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| 10. |
- Gustafsson, Mats, et al.
(author)
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Antenna Current Optimization using MATLAB and CVX
- 2016
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In: FERMAT. ; 15
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Journal article (peer-reviewed)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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