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Resonances, i.e., extrema of the eigenvalues of characteristic modes for closed perfectly conducting objects are investigated. The characteristic modal solutions based on the electric, magnetic, and combined field integral operators (EFIO, MFIO, and CFIO) are studied and compared with analytical solutions for a sphere. All these formulations are found to capture both external (radiating) and internal (cavity) resonances predicted by the analytical expressions. At the internal resonances, the eigenvalues obtained with the EFIO- and MFIO-based approaches are not correct, and the corresponding modes are nonunique. These solutions also exhibit a strong duality between the electric (TM) and magnetic (TE) type modes. A connection is found between the external and internal resonances and the condition numbers of the matrices. The modal expansion of the CFIO-based solution is correct, even though it also experiences the nonuniqueness of the EFIO- and MFIO-based solutions. [ABSTRACT FROM PUBLISHER]

The Finite-Difference Time-Domain (FDTD) method is used to study the frequency dependence of the transmission through a plasmonic screen with slots of sizes and spacing that were chosen using the spatially shifted beam approach to achieve subwavelength focusing. It is shown that the electric field beamwidth at the focal plane exhibits a resonance-like behavior in the vicinity of the frequency for which the meta-screen was designed to work. At this frequency range, the power flow path is shown to exhibit circulation around the slotted screen. Results are also compared with those given in [1] for a similar device working at a lower frequency range where the metallic screen behaves as a perfect electric conductor. [ABSTRACT FROM PUBLISHER]

This work extends the mathematical formulation of the iterative-field-matrix method for observed data from the near-field region of a Perfect Electric Conductor. The method is used as a diagnosis tool for reflector antennas, to determine the positions and extent of distortions from their idealized shapes. The new formulation is tested on a reflector antenna with several significant bumps, and excellent results are achieved. This work also presents an example where the Method of Moments is used to generate the synthetic data and the inversion is performed using Physical Optics. Such a configuration ensures that the forward model is unbiased with respect to the inversion model, demonstrating that the new formulation is also robust for these realistic scenarios. [ABSTRACT FROM PUBLISHER]

Calderón preconditioned electric-field integral equation (CP-EFIE) is very efficient in analyzing electromagnetic problems with a moderate electrical size. For the analysis of electrically large problems with closed surfaces, the CP-EFIE, however, suffers from the well-known spurious internal resonance problem because both the EFIE and the Calderón preconditioner are singular at resonant frequencies. In this paper, the resonance problem of the Calderón preconditioner is removed by using a complex wavenumber, and that of the EFIE is eliminated by enforcing the boundary condition n̂ · D = ρs to the EFIE, resulting in the so-called augmented EFIE (AEFIE). It is shown that the proposed Calderón preconditioned AEFIE is a resonant-free formulation, and has a fast convergence rate for an iterative solution. Numerical examples are given to demonstrate the good accuracy and fast convergence of the proposed approach for the analysis of electrically large problems. The multilevel fast multipole algorithm (MLFMA) is employed to reduce the computational and storage complexities of the iterative solution. [ABSTRACT FROM PUBLISHER]

The article investigates the application of three different ground planes for antenna performance enhancement. They are the conventional perfect electric conductor, the perfect magnetic conductor and their combination. A half-wavelength dipole in free space is considered as the reference case and its performance over these ground planes is investigated and compared.

A compact quarter-wave plate (QWP) based on a doubly periodic subwavelength hole array lying over a dielectric slab is synthesized analytically under perfect electric conductor assumption and its validity is demonstrated numerically for real metals (aluminum and silver) at terahertz (THz) and near infrared. The form birefringence is achieved via the excitation of transverse-magnetic and transverse-electric extraordinary transmission resonances for the perpendicular and parallel polarization to the short in-plane period, respectively. To prove the generality of the approach, a prototype working at the near-infrared is designed and numerically optimized. By imposing a maximum phase deviation of ±10° from the ideal QWP response and an axial ratio smaller than 3 dB, the bandwidth of the designs are 0.6% and 0.4% for the 0.23-λ-thick THz and 0.33- λ-thick near-infrared prototype, respectively. Given the simplicity of the design, it holds promise for compact narrowband microwaves-to-visible polarizing devices. [ABSTRACT FROM PUBLISHER]

A radar cross section (RCS) measurement setup for the characterization and measurement of periodic structures is presented. The idea is to modify an existing spherical range in an anechoic-chamber setup, allowing scattered-field measurements of PEC and artificial magnetic conductor prototypes. With the proposed setup, the scattered field of the object under test (OUT) can be measured for different azimuth and roll angles, as well as for any incident wave polarization. The measurement setup's performance is validated by comparing simulations and measurements. Finally, a combined PEC-artificial magnetic conductor surface, intended for RCS reduction, was measured with the proposed setup. [ABSTRACT FROM PUBLISHER]