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State‐space models and stored electromagnetic energy for antennas in dispersive and heterogeneous media
Author(s) -
Gustafsson Mats,
Ehrenborg Casimir
Publication year - 2017
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1002/2017rs006281
Subject(s) - lorentz transformation , quadratic equation , antenna (radio) , physics , debye , energy (signal processing) , dipole , electromagnetic field , computational physics , electrical conductor , mathematical analysis , mathematics , computer science , telecommunications , classical mechanics , quantum mechanics , geometry
Accurate and efficient evaluation of the stored energy is essential for Q factors, physical bounds, and antenna current optimization. Here it is shown that the stored energy can be estimated from quadratic forms based on a state‐space representation derived from the electric and magnetic field integral equations. The derived expressions are valid for small antennas embedded in temporally dispersive and inhomogeneous media. The quadratic forms also provide simple single frequency formulas for the corresponding Q factors. Numerical examples comparing the different Q factors are presented for dipole and meander line antennas in conductive, Debye, and Lorentz media for homogeneous and inhomogeneous media. The computed Q factors are also verified with the Q factor obtained from the stored energy in Brune synthesized circuit models.