Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPerfect conversion of a TM surface-wave into a TM leaky-wave by an isotropic periodic metasurface printed on a grounded dielectric slab
69
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
This paper presents an exact solution for a perfect conversion of a TM-polarized surface wave (SW) into a TM-polarized leaky-wave (LW) using a reciprocal and lossless penetrable metasurface (MTS) characterized by a scalar sheet impedance, located on a grounded slab. In contrast to known realizations of leaky-wave antennas, the optimal surface reactance modulation which is found here ensures the absence of evanescent higher-order modes of the field Floquet-wave expansion near the radiating surface. Thus, all the energy carried by the surface wave is used for launching the single inhomogeneous plane wave into space without accumulation of reactive energy in the higher-order modes. It is shown that the resulting penetrable MTS exhibits variation from an inductive to a capacitive reactance passing through a resonance. The present formulation complements a previous paper of the authors in which a perfect conversion from TM-polarized SW to TE-polarized LW was found for impenetrable boundary conditions. Here, the solution takes into account the grounded slab dispersion and it is convenient for practical implementation.
rate research
Read More
In this paper, theoretical and numerical studies of perfect/nearly-perfect conversion of a plane wave into a surface wave are presented. The problem of determining the electromagnetic properties of an inhomogeneous lossless boundary which would fully transform an incident plane wave into a surface wave propagating along the boundary is considered. An approximate field solution which produces a slowly growing surface wave and satisfies the energy conservation law is discussed and numerically demonstrated. The results of the study are of great importance for the future development of such devices as perfect leaky-wave antennas and can potentially lead to many novel applications.
Although a rigorous theoretical ground on metasurfaces has been established in the recent years on the basis of the equivalence principle, the majority of metasurfaces for converting a propagating wave into a surface wave are developed in accordance with the so-called generalized Snells law being a simple heuristic rule for performing wave transformations. Recently, for the first time, Tcvetkova et al. [Phys. Rev. B 97, 115447 (2018)] have rigorously studied this problem by means of a reflecting anisotropic metasurface, which is, unfortunately, difficult to realize, and no experimental results are available. In this paper, we propose an alternative practical design of a metasurface-based converter by separating the incident plane wave and the surface wave in different half-spaces. It allows one to preserve the polarization of the incident wave and substitute the anisotropic metasurface by an omega-bianisotropic one. The problem is approached from two sides: By directly solving the corresponding boundary problem and by considering the ``time-reversed scenario when a surface wave is converted into a nonuniform plane wave. We develop a practical three-layer metasurface based on a conventional printed circuit board technology to mimic the omega-bianisotropic response. The metasurface incorporates metallic walls to avoid coupling between adjacent unit cells and accelerate the design procedure. The design is validated with full-wave three-dimensional numerical simulations and demonstrates high conversion efficiency.
In this paper, a novel concept of a leaky-wave antenna is proposed, based on the use of Huygens metasurfaces. It consists of a parallel-plate waveguide in which the top plate is replaced by a bianisotropic metasurface of the Omega type. It is shown that there is an exact solution to transform the guided mode into a leaky-mode with arbitrary control of the constant leakage factor and the pointing direction. Although the solution turns out to be periodic, only one Floquet mode is excited and radiates, even for electrically long periods. Thanks to the intrinsic spurious Floquet mode suppression, broadside radiation can be achieved without any degradation. Simulations with idealized reactance sheets verify the concept. Moreover, physical structures compatible with PCB fabrication have been proposed and designed, considering aspects such as the effect of losses. Finally, experimental results of two prototypes are presented and discussed.
We show that there exists an exact solution for a lossless and reciprocal periodic surface impedance which ensures full conversion of a single-mode surface wave propagating along the impedance boundary to a single plane wave propagating along a desired direction in free space above the boundary. In contrast to known realizations of leaky-wave antennas, the optimal surface reactance modulation which is found here ensures the absence of evanescent higher-order modes of the Floquet wave expansion of fields near the radiating surface. Thus, all the energy carried by the surface wave is used for launching the single inhomogeneous plane wave into space, without accumulation of reactive energy in higher-order modes. The results of the study are expected to be useful for creation of leaky-wave antennas with the ultimate efficiency, and, moreover, can potentially lead to novel applications, from microwaves to nanophotonics.
We investigate the possibility to model a metasurface, defined as a zero-thickness sheet of surface polarization currents, by a thin slab, characterized by a subwavelength thickness and usual voluminal medium parameters. First, we elaborate a general equivalence relation between the metasurface and the slab in terms of average electromagnetic fields. Then, we derive exact relations between the metasurface and slab susceptibilities and validate them by full-wave simulations. Finally, we discuss the simple and insightful Average Field Approximation (AFA) formula, illustrate its inappropriate for strong metasurface field transformations, and establish its range of validity. All of these developments are restricted to the simplest case of a uniform isotropic metasurface under normal plane wave incidence. We conclude from the complexity of the equivalence for this case, that a metasurface is generally best modeled in terms of Generalized Sheet Transition Conditions (GSTCs).
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
