A systematic and efficient multimodal transfer-matrix approach is proposed for the comprehensive Bloch analysis of general 1-D/2-D/3-D periodic structures. We provide a linearization procedure for transforming the original nonlinear eigenvalue problem associated with 2-D/3-D structures to a standard one that can easily be solved without the need of a zero-searching algorithm in the complex plane. The proposed approach has been validated with bounded/open structures with complex geometries and/or inhomogeneous lossless/lossy materials. It demonstrates a significantly reduced computational time and leverages the strengths of full-wave simulators to deal with general problems and ad hoc quasi-analytical methods to give a fundamental understanding of the behavior of the structure. Also, it allows for an accurate evaluation of the imaginary part of the wavenumber, which offers information of material dissipation, stopband rejection, leakage, and complex modes.

An anisotropic unit cell based on glide symmetry is proposed for tailoring a metasurface that engineers an optically transformed Luneburg lens. Thanks to the optical transformation, the size of the lens is reduced by 25%. The proposed lens is ultrawideband, and it covers multi-octave frequency bands. The required constitutive materials are achieved in an air gap bounded by top and bottom glide-symmetric metasurfaces; i.e., they are off-shifted by half the period. Each surface is implemented in standard printed-circuit-board technology, and its unit cell consists of a grounded substrate with an elliptical holey top cladding surrounded by metalized through-vias. This technology, known as substrate-integrated-holes (SIHs), mimics the operation of holes drilled in a parallel plate but provides the higher effective refractive index required for lens compression. The SIH is attractive for practical applications since most of the energy propagates in the air gap between the two surfaces and, therefore, it features low dielectric losses. Thanks to glide symmetry, the proposed metasurface demonstrates a further enhanced effective refractive index with lower dispersion over an ultra-wide bandwidth in comparison to its non-glide counterpart. A multimodal transfer-matrix approach is here employed to carry out the Bloch analysis of the proposed SIH.

A novel and general approach is presented for the complete suppression of the open-stopband (OSB) effects in circularly polarized 1-D periodic leaky-wave antennas (LWAs) using anisotropic modulated metasurfaces (MTSs). A theoretical justification of this behavior is found through the rigorous treatment of the canonical problem of an infinite homogenized impedance surface sinusoidally modulated along the propagation direction. By deriving a closed-form solution of this problem at broadside scan, it is shown that, while the sinusoidally modulated isotropic impedance exhibits a null of the attenuation constant, the complex propagation constant for the proposed anisotropic modulation has a finite value and a regular behavior. A closed-form formula for the leakage constant $\boldsymbol {\alpha }$ is also derived, allowing for an accurate design of the aperture field amplitude. The full-wave analysis of a patch-based implementation of the MTS is in excellent agreement with the results based on the homogenized impedance model, thus demonstrating the practical applicability of the theoretical results. The elimination of the OSB behavior allows for the design of LWAs able to scan the beam from backward (BWD) to forward (FWD) without any frequency regions of blindness.

Open stopband (OSB) mitigation techniques are commonly used to improve the far-field radiating properties of leaky-wave antennas based on periodic structures. Recently, leaky waves have been proposed to focus energy in the near field through Bessel beams. However, the focusing character of Bessel beams is notably limited to a maximum distance known as the nondiffractive range. In this work, an OSB mitigation technique is originally exploited to significantly extend the nondiffractive range of a Bessel beam generated by a leaky-wave launcher in the microwave/millimeter-wave range. A comprehensive analysis of this device is presented, comparing the performance of the proposed launcher with the typical structure of a leaky-wave Bessel-beam launcher where the OSB is not suppressed. Theoretical results, corroborated by full-wave simulations, demonstrate that the proposed device achieves an impressive nondiffractive range of about 25 m. The latter, at 30 GHz, approximately corresponds to 2500 wavelengths (in vacuum) and to 50 times the aperture diameter which is about 50 cm. These results look particularly attractive for, e.g., near-field communications and wireless power transfer applications, where focusing energy in narrow regions and over large distances is a key factor.

Metasurfaces (MTSs) are efficient tools for controlling electromagnetic radiation and manipulating local aperture fields. Anomalous refractors, electromagnetic devices capable of altering the direction of incident plane-waves, have gained significant attention in recent research. Various design approaches have been explored, necessitating a comprehensive comparison to identify the optimal approach. This study evaluates the effectiveness of three different approaches for the design of three-layer anomalous refractors and the selection of the optimal one. The first two approaches employ local approximations, deriving sheet admittance profiles analytically based on the uniform problem matching the local structure. These approaches are referred to as impedance-equalized Huygens’ (IEH) MTS and omega-type bianisotropic (O-BMS) MTS. The third approach, denoted as Floquet-modes optimization (FM-OPT), introduces a numerical technique based on surface field harmonics optimization. In this case, a user-specified number of evanescent Floquet modes (FMs) is employed in the optimization procedure for minimizing the real part of the admittance sheets. The aforementioned approaches are compared for the design of three-layer anomalous refractors performing three different anomalous refractions 0°-to-20°/50°/80° for two different inter-layer distances. An ad hoc multilayer analysis tool based on FM expansion is developed to accurately analyze and compare the designed anomalous refractors. The numerical results indicate that, for practical applications, the FM-OPT approach outperforms both the IEH and O-BMS approaches in terms of performance and accuracy.

Anisotropic Self‐Complementary Metasurfaces (SC‐MTSs) are structures constituted by an alternation of complementary inductive and capacitive strips, which are “self‐dual” according to Babinet’s duality principle. They support the propagation of two orthogonally polarized surface‐wave modes with the same phase velocity along the principal directions (i.e., along the strips and normal to them). The isofrequency dispersion curves of these modes are hyperbolas, and therefore, these MTSs fall in the category of hyperbolic MTSs. It is shown here that the hyperbolic dispersion curves may degenerate in same cases into almost straight lines, which implies that the velocity of energy transport is constantly directed along the same direction for any possible phasing orthogonal to the strips. In this circumstance, the SC‐MTS can be conveniently used to design dual‐polarized leaky‐wave antennas by modulating the impedances of the complementary strips.