Guido Valerio

Comparative Analysis of Acceleration Techniques for 2-D and 3-D Green's Functions in Periodic Structures Along One and Two Directions

The problem of accelerating the calculation of the periodic Greens function is addressed here for both 3-D and 2-D free-space configurations. In the 3-D case, periodicity is considered both along one axis and along two, generally skew, axes. A comprehensive review of the existing methods is first presented and some extensions are developed. The possibility of treating the case of complex phase shifts between unit cells, necessary for the study of complex modes in periodic structures, is also investigated. Comparisons among the various acceleration methods are performed, thus providing fundamental information on their actual efficiency in typical problems.

On-Body Propagation at 60 GHz

The on-body propagation at 60 GHz is studied analytically, numerically and experimentally using a skin-equivalent phantom. First, to provide analytical-based fundamental models of path gain, the theory of propagating waves near a flat phantom is studied by considering vertical and horizontal elementary dipoles. The analytical models are in excellent agreement with full-wave simulations. For a vertically polarized wave, a minimum power decay exponent of 3.5 is found. Then, propagation on the body is investigated experimentally in vertical and horizontal polarizations using two linearly-polarized open-ended waveguides. The analytical models fit very well with the measurements. Furthermore, the effect of polarization on the antenna performance is studied numerically and experimentally.

Regularization of Mixed-Potential Layered-Media Green's Functions for Efficient Interpolation Procedures in Planar Periodic Structures

The problem of improving the computational efficiency in the numerical analysis of planar periodic structures is investigated here using the mixed-potential integral-equation (MPIE) approach. A new regularization of the periodic Greens functions (PGFs) that are involved in the analysis of multilayered structures is introduced, based on the effective-medium concept. This regularization involves extracting the singularities of the PGFs up to second-order terms. The resulting regularized PGF is very smooth and amenable to interpolation. Thus, optimized interpolation procedures for the PGFs can be applied, resulting in a considerable reduction of computation time without any significant effect on the accuracy. Another benefit of the regularization is that it significantly enhances the convergence of the series for both the vector- and scalar-potential PGFs. The theoretical formulation is fully validated with various numerical results for both two-dimensional (2-D) and one-dimensional (1-D) layered-media periodic structures.

On the Near-Field Shaping and Focusing Capability of a Radial Line Slot Array

We describe the design of a radial line slot array antenna with a shaped and focused near field. The antenna is designed in such a way to control the side lobe level and beamwidth of the normal component of the electric field with respect to the radiating aperture. The design procedure consists of two steps. In the first step, the requirements on the near-field pattern are provided over a focusing plane at a given distance from the radiating aperture. A set theoretic approach is then used to derive the aperture field distribution fitting the requirements over the near field. In the second step, the aperture field distribution is synthesized by accurately placing and sizing the slots of the antenna. The spillover efficiency is maximized during the design process. The antenna is centrally fed by a simple coaxial probe. The antenna design is validated by a prototype and measurements at 12.5 GHz.

Accurate Bloch Analysis of 1-D Periodic Lines Through the Simulation of Truncated Structures

A common approach to perform dispersive analyses of waveguides periodic along one direction is based on the electromagnetic simulation of a single spatial period of the structure. However, the resulting equivalent two-port network representation of the single cell may lead to inaccurate modal results, since mutual coupling between cells has been neglected. When a finite number of adjacent cells are simulated, with the aim of improving the accuracy of the analysis, spurious solutions are introduced; they are shown here to be related to the nonuniqueness of root-extraction operations in the complex plane. A simple automatic method is proposed to recover the correct solution and to test the convergence of the analysis as the number of simulated cells is increased.

A Full-Wave Hybrid Method for the Analysis of Multilayered SIW-Based Antennas

We propose a fast and accurate full-wave code capable of analyzing electrically large substrate integrated waveguides consisting of stacked parallel-plate waveguides hosting dielectric or metallic posts and coupling and/or radiating slots. Boundary conditions enforced on posts yield scattering amplitudes, while slots are modeled by equivalent magnetic currents, solved by a method of moments. Substantial accelerations are proposed to exploit various symmetries of the structures and to select the optimal number of modes according to the relevant geometrical and physical parameters. The formulation is validated by full-wave simulations with a commercial software and measurement results.

Self-Polarizing Fabry–Perot Antennas Based on Polarization Twisting Element

A new configuration of a self-polarizing Fabry-Perot (FP) antenna is presented to generate circular polarization with high gain levels using a simple linearly polarized feed. It consists of an FP resonator combined with a polarization-twisting ground plane. An analytical model is proposed to facilitate the antenna design, and the corresponding results are shown to be in very close agreement with full-wave simulations. The experimental prototype built in -band exhibits a combined bandwidth (3 dB axial ratio, 3 dB gain drop, and 10 dB impedance matching) of 3% with a maximum realized gain of 18.0 dB. The antenna is completely shielded with an aperture size of and a height of only . Such antennas are attractive candidates for high-power space applications at low frequencies ( -to -bands) where standard horns are very bulky.

Enhancement of On-Body Propagation at 60 GHz Using Electro Textiles

It is demonstrated that an electro textile can improve the wave propagation at 60 GHz along and around the body. To this end, an analytical formulation is implemented to evaluate the electric field excited by an infinitesimal dipole over a flat skin model with and without an electro textile layer. To validate the analytical results, the propagation is characterized numerically and experimentally for two rectangular open-ended V-band waveguides placed over a skin-equivalent phantom. Path gain values for flat, cylindrical, and elliptical cylinder phantoms are provided. Results show that placing an electro textile over a skin-equivalent phantom allows increasing the path gain by 5-15 dB. In addition, it has a shielding effect by decreasing the power absorption in the body by more than 95%.

Formulas for the Number of Surface Waves on Layered Structures

Closed-form expressions are derived for the number of surface waves propagating along a general multilayered structure with media having positive material parameters. The expressions shown here are also useful for the efficient numerical determination and ordering of the cutoff frequencies of surface waves on multilayered structures. The presented formulas are simple but exact. Validation is provided with full-wave dispersive analyses of several types of layered structures.

Fundamental properties of surface waves in lossless stratified structures

This paper is focused on dispersive properties of lossless planar layered structures with media having positive constitutive parameters (permittivity and permeability), possibly uniaxially anisotropic. Some of these properties have been derived in the past with reference to specific simple layered structures, and are here established with more general proofs, valid for arbitrary layered structures with positive parameters. As a first step, a simple application of the Smith chart to the relevant dispersion equation is used to prove that evanescent (or plasmonic-type) waves cannot be supported by layers with positive parameters. The main part of the paper is then focused on a generalization of a common graphical solution of the dispersion equation, in order to derive some general properties about the behaviour of the wavenumbers of surface waves as a function of frequency. The wavenumbers normalized with respect to frequency are shown to be always increasing with frequency, and at high frequency they tend to the highest refractive index in the layers. Moreover, two surface waves with the same polarization cannot have the same wavenumber at a given frequency. The low-frequency behaviours are also briefly addressed. The results are derived by means of a suitable application of Foster’s theorem.