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The theory of characteristic modes (TCM) is presented for arbitrarily shaped 3-D structures including perfect electric conductors (PECs) and homogeneous penetrable objects. It is shown that by properly expressing the weighting operator of the generalized eigenvalue equation in terms of the integral operators related to the radiated fields, TCM can be formulated directly for the surface integral equation formulation of the problem. This avoids symmetrization or other modifications of the equations. The eigenvalues are shown to be related to radiated, reactive, and dissipated power, and the corresponding far-field patterns are orthogonal. The previously introduced TCM formulations for PEC are special cases of this generalized TCM.

Metasurfaces are used to design mantle cloaks based on scattering cancellation which involves surface impedance analysis. Theory of characteristic modes is a good tool for analyzing the scattering of a metallic object because it is based on surface impedance and it brings physical insight into the radiation properties of a structure without an excitation source. The theory of characteristic modes is applied in the analysis of a cylindrical cloaking metasurface used to cloak an LTE antenna to prevent it from interfering with a UMTS antenna when both antennas are co-located on the same site. The result provides a physical insight into the principle and design of mantle cloaks. It shows that degenerate resonant modes of the cloak are used to compensate for the degenerate non-resonant modes of the antenna. There is a symmetry in the modal surface current distribution of the cloak and the direction of the fundamental modal current distribution of the cloak is at 90° to that of the UMTS antenna. Also, the UMTS antenna has a better impedance matching after cloaking.

This paper describes the application of the theory of characteristic modes to excite a conducting cylinder representing the chassis of a rocket. Mode excitation is achieved by cutting H-shaped slots on the cylinder at specific locations where the maximum of modal current distribution occurs. The L-matching network is designed to match the impedance of the slots to the input coaxial cable. Finally, the proposed concept is verified during manufacturing and measurement. It is shown that the measured results are in excellent agreement with the simulation.

AP-S/URSI 2019, IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, Atlanta, ETATS-UNIS, 07-/07/2019 - 12/07/2019; High sensitivity in sensors, large group delays forfilters and slow light can be achieved by engineering electromag-netically induced transparency within a narrow electromagneticspectrum. The induced transparency is due to the eliminationof the effect of a medium caused by interaction betweentwo resonant states often referred to as the bright and darkmodes. Induced transparency are often attained by breaking thestructural symmetry of metamaterials as this allows interactionbetween the two modes. In a case of a given excitation, thereis a need to understand the behaviour of the various modesthus making the application of theory of characteristic modesrelevant to this work. This paper presents an approach toobtain electromagnetically induced transparency for a givenexcitation using the theory of characteristic modes. It presentshow electromagnetically induced transparency in a structurecan be systematically engineered by determining which modesare responsible for its occurrence and how to excite thesemodes. In our example, EIT occurred at 36 GHz wherethere was an interaction between the bright and dark modes.This provides an insightful way for designing structures forelectromagnetically induced transparency applications

In this letter, new metrics are proposed to provide physical insight into the behavior of metamaterial based structures by means of the theory of characteristic modes. A relationship between the first eigenmode and an expression of the polarizability is proposed for a split ring resonator. It thus allows us to describe a link between the artificial magnetic response of a split ring resonator and modal characteristics. Using the new metrics proposed, a reactive impedance substrate based on metal-dielectric metamaterial excited by a parallel magnetic field is shown to exhibit artificial magnetism. These metrics are shown to propose good agreement with other analytical and numerical methods. This analysis should be useful when such metal-dielectric metamaterial structures are associated to radiating elements like antennas, since it could be performed in the near field region, unlike common approaches based on plane wave and far field assumptions.

A planar extremely-wide-band antenna is designed and simulated. Measurements are presented. The proposed antenna is a printed elliptical slotted monopole with a triangular ground plane, fed by a semi-ring trident arm followed by a tapered CPW line. The frequencies covered for a VSWR $ \leq 2$ extend from 0.67 GHz to 12 GHz with stable radiation patterns to ensure minimal pulse distortion. This is guaranteed by multimodal analysis of the radiating current on the radiator using the theory of characteristic modes. Numerical and experimental results are in good agreement. This novel miniaturized antenna ( $0.15 \times 0.07{\lambda _l}$ , where ${\lambda _l}$ corresponds to the wavelength of the lowest matched frequency) is a good candidate for wide-band spectrum sensing in the TV white space band in the context of cognitive radio applications.

The creation of a magnetic boundary condition into the plane of symmetry in a radiating ground plane of a portable device is proposed to enhance its radiation efficiency and bandwidth. This magnetic boundary condition is achieved by exciting the antenna through symmetrical feeding. A novel antenna consisting of a symmetrical folded dipole is presented in order to exemplify how a broad bandwidth and very good radiation properties can be obtained with the proposed technique. The Theory of Characteristic Modes is used to analyze and compare a folded dipole with the symmetrical folded dipole. This study shows how the magnetic boundary condition favors excitation of antenna modes in a broad bandwidth while avoiding excitation of transmission line modes. Two different prototype antennas, a monopole and a symmetrical folded dipole with an LC-balun, were implemented and measured. The measured -6 dB impedance bandwidth of the monopole extends from 0.95 GHz to 2.15 GHz. In turn, the bandwidth of the symmetrical folded dipole extends from 0.90 GHz to 1.96 GHz. The average of the measured total efficiencies at the aforementioned bandwidth is -1.6 dB for both prototypes. The measured maximum total gain at 0.95 GHz is 2.6 dBi for the monopole and 1.9 dBi for the symmetrical folded dipole. © 2011 IEEE., This work was supported by the Finnish Funding Agency for Technology and Innovation, Nokia Devices Oulu, and Pulse Finland. The work of M. Sonkki was supported by the Universidad Politecnica de Valencia and COST IC0603 ASSIST.