| 1. |
- Alayon Glazunov, Andres, et al.
(author)
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Physical Modeling of MIMO Antennas and Channels by Means of the Spherical Vector Wave Expansion
- 2009
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Reports (other academic/artistic)abstract
- In this paper we propose a new physically motivated model that allows to study the interaction between the antennas and the propagation channel for Multiple-Input Multiple-Output (MIMO) systems. The key tools employed in the model are the expansion coefficients of the electromagnetic field in spherical vector waves and the scattering matrix representation of the properties of the antenna. We derive the expansion of the MIMO channel matrix, H, in spherical vector wave modes of the electromagnetic field of the antennas as well as the propagation channel. We also introduce the channel scattering dyadic, C, with a corresponding correlation model for co- and cross-polarized elements and introduce the concept of mode-to-mode channel mapping, the M-matrix, between the receive and transmit antenna modes. The M-matrix maps the modes excited by the transmitting antenna to the modes exciting the receive antennas and vice versa. The covariance statistics of this M-matrix are expressed as a function of the double-directional power-angular spectrum (PAS) of co- and cross-polarized components of the electromagnetic field. Our approach aims at gaining insights into the physics governing the interaction between antennas and channels and it is useful for studying the performance of different antenna designs in a specified propagation channel as well as for modeling the propagation channel. It can furthermore be used to quantify the optimal properties of antennas in a given propagation channel. We illustrate the developed methodology by analyzing the interaction of a 2x2 system of slant polarized half-wavelength dipole antennas with some basic propagation channel models.
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| 2. |
- Alayon Glazunov, Andres, et al.
(author)
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Spherical Vector Wave Expansion of Gaussian Electromagnetic Fields for Antenna-Channel Interaction Analysis
- 2008
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Reports (other academic/artistic)abstract
- In this paper we introduce an approach to analyze the interaction between antennas and the propagation channel. We study both the antennas and the propagation channel by means of the spherical vector wave mode expansion of the electromagnetic field. Then we use the expansion coefficients to study some properties of general antennas in those fields by means of the antenna scattering matrix. The focus is on the spatio-polar characterization of antennas, channels and their interactions. We provide closed form expressions for the covariance of the field multi-modes as function of the Power Angle Spectrum (PAS) and the channel cross-polarization ratio (XPR). A new interpretation of the Mean Effective Gains (MEG) of antennas is also provided. The maximum MEG is obtained by conjugate mode matching between the antennas and the channel; we also prove the (intuitive) results that the optimum decorrelation of the antenna signals is obtained by the excitation of orthogonal spherical vector modes.
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| 3. |
- Bernland, Anders, et al.
(author)
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Estimation of Spherical Wave Coefficients from 3D Positioner Channel Measurements
- 2012
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Reports (other academic/artistic)abstract
- Electromagnetic vector spherical waves have been used recently to model antenna channel interaction and the available degrees of freedom in MIMO systems. However, there are no previous accounts of a method to estimate spherical wave coefficients from channel measurements. One approach, using a 3D positioner, is presented in this letter, both in theory and practice. Measurement results are presented and discussed. One conclusion is that using randomly positioned measurements within a volume is less sensitive to noise than using only measurements on the surface.
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| 4. |
- Bernland, Anders, et al.
(author)
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Physical limitations on the scattering of electromagnetic vector spherical waves
- 2010
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Reports (other academic/artistic)abstract
- Understanding the interaction between electromagnetic waves and matter is vital in applications ranging from classical optics to antenna theory. This paper derives physical limitations on the scattering of electromagnetic vector spherical waves. The assumptions made are that the heterogeneous scatterer is passive, and has constitutive relations which are on convolution form in the time domain and anisotropic in the static limit. The resulting bounds limit the reflection coefficient of the modes over a frequency interval, and can thus be interpreted as limitations on the absorption of power from a single mode. They can be used within a wide range of applications, and are particularly useful for electrically small scatterers. The derivation follows a general approach to derive sum rules and physical limitations on passive systems on convolution form. The time domain versions of the vector spherical waves are used to describe the passivity of the scatterer, and a set of integral identities for Herglotz functions are applied to derive sum rules from which the physical limitations follow.
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| 5. |
- Bernland, Anders, et al.
(author)
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Sum rules and constraints on passive systems
- 2010
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Reports (other academic/artistic)abstract
- A passive system is one that cannot produce energy, a property that naturally poses constraints on the system. A system on convolution form is fully described by its transfer function, and the class of Herglotz functions, holomorphic functions mapping the open upper half plane to the closed upper half plane, is closely related to the transfer functions of passive systems. Following a well-known representation theorem, Herglotz functions can be represented by means of positive measures on the real line. This fact is exploited in this paper in order to rigorously prove a set of integral identities for Herglotz functions that relate weighted integrals of the function to its asymptotic expansions at the origin and infinity. The integral identities are the core of a general approach introduced here to derive sum rules and physical limitations on various passive physical systems. Although similar approaches have previously been applied to a wide range of specific applications, this paper is the first to deliver a general procedure together with the necessary proofs. This procedure is described thoroughly, and exemplified with examples from electromagnetic theory.
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| 6. |
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| 7. |
- Cismasu, Marius, et al.
(author)
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Antenna Bandwidth Optimization with Single Frequency Simulation
- 2013
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Reports (other academic/artistic)abstract
- A method to compute antenna Q using an electromagnetic simulation at a single frequency is described. This method can easily be integrated into global optimization algorithms. In this way the optimization time of some antenna parameters, e.g., bandwidth, may be significantly reduced. The method is validated by direct comparison with the physical bound of the analyzed structure. Numerical examples for rectangular antennas and antennas with a rectangular ground plane illustrate the integration of the method into a genetic algorithm. The results predicted by optimization agree very well with those obtained using a commercial electromagnetic solver. These results suggest that the method can be used to yield antennas with Q factors within 20% of their corresponding physical bound.
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| 8. |
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| 9. |
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| 10. |
- Ehrenborg, Casimir, et al.
(author)
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Bandwidth-Constrained Capacity Bounds on MIMO Antennas
- 2019
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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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