Physical Bounds of Antennas

Gustafsson, Mats; Tayli, Doruk; Cismasu, Marius

doi:10.1007/978-981-4560-44-3_18

Cited by 14 publications

(40 citation statements)

References 96 publications

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“…Directivity higher than a nominal directivity is often referred to as superdirectivity and associated with low efficiency and narrow bandwidth [7]. The trade-off between the Q-factor and directivity was shown in [15] and further investigated in [36], [42], [50]. Superdirectivity is also associated with decreased radiation efficiency or equivalently an increased dissipation factor (22).…”

Section: Superdirectivitymentioning

confidence: 99%

Maximum Gain, Effective Area, and Directivity

Gustafsson

Čapek

2019

IEEE Trans. Antennas Propagat.

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Fundamental bounds on antenna gain are found via convex optimization of the current density in a prescribed region. Various constraints are considered, including self-resonance and only partial control of the current distribution. Derived formulas are valid for arbitrarily shaped radiators of a given conductivity. All the optimization tasks are reduced to eigenvalue problems, which are solved efficiently. The second part of the paper deals with superdirectivity and its associated minimal costs in efficiency and Q-factor. The paper is accompanied with a series of examples practically demonstrating the relevance of the theoretical framework and entirely spanning wide range of material parameters and electrical sizes used in antenna technology. Presented results are analyzed from a perspective of effectively radiating modes. In contrast to a common approach utilizing spherical modes, the radiating modes of a given body are directly evaluated and analyzed here. All crucial mathematical steps are reviewed in the appendices, including a series of important subroutines to be considered making it possible to reduce the computational burden associated with the evaluation of electrically large structures and structures of high conductivity.

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Section: Superdirectivitymentioning

confidence: 99%

Maximum Gain, Effective Area, and Directivity

Gustafsson

Čapek

2019

IEEE Trans. Antennas Propagat.

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“…These bounds have been verified by optimizing the same problems in CVX [18], [23] for several of the considered cases confirming that the duality gap is zero for these cases. However, it is also interesting to investigate the radiation modes that contribute to the spectral efficiency in (15). To illustrate both of these results this section is divided into four sub-sections.…”

Section: Resultsmentioning

confidence: 99%

“…In Section III it is shown that the only part of the optimal spectral efficiency problem (8) that is dependent on the geometry considered are the eigenvalues n of the radiation modes. This means that optimizing spectral efficiency with a radiation efficiency constraint has been reduced to solving the generalized eigenvalue problem (16), followed by water filling over the singular values σ n given by (15) or (17). This means that it is possible to evaluate the quality of a geometry, in terms of spectral efficiency, by only studying the eigenvalues n of (15) for normalized radiated power on the left and from (17) for normalized dissipated power on the right.…”

Section: Radiation Modesmentioning

confidence: 99%

“…Since both of its constituent matrices are positive definite this implies that ν > ν 0 , where ν 0 is the lower limit at which R ν is positive semidefinite. The lower limit can be established by studying the eigenvalue problem in (15), (ν + η −1 − 1) n 1 + ν n ≥ 0,…”

Section: Appendix C ν Intervalmentioning

confidence: 99%

“…Current optimization has been utilized to construct fundamental bounds on many different antenna parameters previously, such as, Q, directivity, and efficiency [12], [14], [15], [16], [17]. By controlling the current density in the full design space of the antenna an optimal solution can be reached for that configuration.…”

Section: Introductionmentioning

confidence: 99%

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Physical Bounds and Radiation Modes for MIMO Antennas

Ehrenborg

Gustafsson

2020

IEEE Trans. Antennas Propagat.

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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 electrically 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. This bound is also studied for N -degree MIMO systems. For electrically large 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 computationally efficient solution for this problem is formulated and investigated in relation to constraining parameters, such as size and efficiency.

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Bandwidth of Singular Plasmonic Resonators in Relation to the Chu Limit

et al. 2021

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Plasmonic nanostructures with singular geometries can exhibit a broadband scattering response that at first glance appears to violate the lower bounds for the radiation quality (Q) factor of small radiators, known as the Chu limit. Here we explore this apparent contradiction, investigating the Q factor of the resonant modes supported by two nearly touching cylinders, and analyze how their fractional bandwidth fares in relation to the Chu limit. We first derive lower bounds for the radiation Q factors of two-dimensional objects of an arbitrary cross-section. We then discuss the dissipation and radiation Q factors associated with the plasmonic resonances of a cylinder dimer as a function of its gap size. We show that the radiation Q factor is always larger than the minimum Q and, as long as the peaks in the scattering spectrum are well separated, their bandwidth is equal to the inverse of their Q factor. In the limit of touching cylinders, the resonance spectra transition from discrete to a continuum around an accumulation point, yielding a broadband response for any finite level of material loss. Within any given frequency interval, the response is the result of a multitude of plasmon resonances, each individually obeying the Chu limit. Nevertheless, the connection between the Q factor and the overall bandwidth of the scattering response is lost. Our study sheds light onto the exotic resonant phenomena emerging when plasmonic materials are shaped in singular geometries, and outlines their opportunities and limitations for nanophotonics.

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Physical Bounds of Antennas

Cited by 14 publications

References 96 publications

Maximum Gain, Effective Area, and Directivity

Maximum Gain, Effective Area, and Directivity

Physical Bounds and Radiation Modes for MIMO Antennas

Bandwidth of Singular Plasmonic Resonators in Relation to the Chu Limit

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