Fabrizio Frezza

Full-Wave Modal Dispersion Analysis and Broadside Optimization for a Class of Microstrip CRLH Leaky-Wave Antennas

In this paper, a planar microstrip composite right/left-handed leaky-wave antenna is analyzed and designed as an infinite 1-D periodic microstrip leaky-wave antenna. A parametric study, based on a full-wave numerical modal approach that analyzes a unit cell using a periodic layered-medium Greens function, is shown to be an efficient approach to accurately design the structure, completely eliminating open-stopband effects and achieving an almost constant radiation efficiency when the beam is scanned through broadside. Results obtained by the proposed approach are compared with those obtained by means of both an artificial transmission-line analysis and a Bloch-wave analysis, which use the full-wave simulation of a finite-length structure. The balanced condition is interpreted in terms of the behavior of the phase and attenuation constants relevant to the radiating harmonic. Furthermore, it is shown how radiation at broadside is guaranteed by the presence of two radiating elements (one series and one shunt) within the equivalent circuit of the unit cell. The effectiveness of the analysis is demonstrated through the design of a finite-length antenna excited by a source at one end.

Generalized Bessel-Gauss beams

In this paper we describe a superposition model for Bessel-Gauss beams, in which higher orders are included. An analogous model leads to a different class of beams, namely the modified Bessel-Gauss beams. Then a generalized set of beams, containing the previous beams as particular cases, is introduced. The behaviour of these beams upon propagation is investigated, both analytically and numerically.

The transition region between bound-wave and leaky-wave ranges for a partially dielectric-loaded open guiding structure

Most modes on partially dielectric-loaded open guiding structures are purely bound in some frequency range and leaky in another. The transition region between them is complicated and interesting, including a section where the dispersion curve doubles back because it connects a complex nonspectral (leaky-wave) solution with a real spectral (bound-wave or surface-wave) solution. The physical nature of this type of transition region is discussed qualitatively, where some anomalous features are considered; then numerical values for a specific example, a recently proposed novel leaky-wave antenna structure, are presented. >

Fundamental modal properties of surface waves on metamaterial grounded slabs

This paper deals with the analysis of surface waves supported by a metamaterial layer on a ground plane, and investigates the potentiality of these grounded slabs as substrates for planar antennas. Both double- and single-negative media, either epsilon- or mu-negative, are considered. As is known, such structures may support two kinds of surface waves, i.e., ordinary (transversely attenuating only in air) and evanescent (transversely attenuating also inside the slab) surface waves. A graphical analysis is performed for proper real solutions of the dispersion equation for TE and TM modes, and conditions are presented that ensure the suppression of a guided-wave regime for both polarizations and kinds of wave. In order to demonstrate the feasibility of substrates with such desirable properties, numerical simulations based on experimentally tested dispersion models for the permittivity and permeability of the considered metamaterial media are reported. Moreover, the effects of slab truncation on the field radiated by a dipole source are illustrated by comparing the radiation patterns at different frequencies both in the presence and in the absence of surface waves. The reported results make the considered structures promising candidates as substrates for planar antennas and arrays with reduced edge-diffraction effects and mutual coupling between elements.

A Novel Technique for Open-Stopband Suppression in 1-D Periodic Printed Leaky-Wave Antennas

A novel technique for the elimination of the open stopband in one-dimensional periodic printed leaky-wave antennas is presented. A quarter-wave transformer, or alternatively a matching stub, is introduced into the unit cell of the antenna, which forces the Bloch-wave impedance of the structure to remain real and non-zero at broadside. The effectiveness of the proposed technique is first demonstrated on a printed periodic microstrip leaky-wave antenna consisting of a single radiating stub per unit cell, which exhibits a significant stopband at broadside. The technique is then also applied to a structure consisting of two radiating stubs per unit cell, which is capable of mitigating, but not eliminating, the open stopband. In both cases the open stopband at broadside is completely suppressed.

Plane-wave scattering by a perfectly conducting circular cylinder near a plane surface: cylindrical-wave approach

A new method for the analysis of the diffraction of a plane wave impinging on a perfectly conducting circular cylinder in front of a generally reflecting surface is presented. The surface is characterized by its complex reflection coefficient, enabling us to treat a wide class of reflecting surfaces. The presence of the surface is taken into account by means of a suitable expansion of the reflected field in terms of cylindrical functions. The method gives the solution of the scattering problem in both the near and the far field regardless of the polarization state of the incident field. Numerical examples for dielectric interfaces are presented, and comparisons are made with results presented in the literature.

Plane wave expansion of cylidrical functions

Abstract Cylindrical waves, i.e. the product of a Hankel function of integer order times a sinusoidal angular factor, often occur in diffraction theory. We derive the expansion of a cylindrical wave into plane waves and we give some examples of applications.

Effects of leaky-wave propagation in metamaterial grounded slabs excited by a dipole source

In this paper, dispersive propagation and radiation properties of leaky waves on metamaterial grounded slabs are investigated. The proper or improper nature of leaky modes supported by such structures is shown to be related to the metamaterial being /spl epsi/-negative, /spl mu/-negative, or double-negative, and to field polarization, giving rise to backward or forward radiation depending on the frequency range of operation. These spectral features and the associated frequency scan of the radiated beam are illustrated by considering the field excited by a dipole source in the presence of an infinite metamaterial grounded slab. The possibility to achieve nearly equal values for the phase constants of a TE and a TM leaky mode on a large frequency range is shown; this allows us to obtain a conical radiation pattern and, also, for suitable values of the attenuation constants, the radiation of a pencil beam at broadside. Conditions for achieving maximum power density at broadside are derived, when one constitutive parameter is much smaller than the other. In order to illustrate these novel features, numerical results based on experimentally tested dispersion models for permittivity and permeability of the metamaterial media are provided, concerning leaky-wave modal properties and near and far fields excited by a dipole source.

A versatile leaky-wave antenna based on stub-loaded rectangular waveguide .I. Theory

A new leaky-wave antenna is presented that possesses many desirable features and is suitable for application to both the millimeter-wave and microwave ranges. These desirable features, some of which are unusual, include a simple configuration, a wide flexibility in the range of available beamwidths, the ability to control the beamwidth and the direction of the beam essentially independently, and negligible cross polarization at all scan angles. The antenna structure consists of a parallel-plate stub guide of small height, less than a half wavelength, located off center on the top of rectangular waveguide. The beamwidth is easily controlled from very wide to very narrow by adjusting the stub width or location. The article presents the principle of operation and the theory, employing a new transverse equivalent network that is accurate, but also simple, so that it permits rapid and inexpensive numerical calculations.

Modal properties of surface and leaky waves propagating at arbitrary angles along a metal strip grating on a grounded slab

A full-wave analysis is presented of the dispersion properties of modes supported by a grounded dielectric slab periodically loaded with metal strips, which represents a canonical configuration employed in planar microwave antennas and arrays and in the realization of artificially hard and soft surfaces. Propagation of surface and leaky modes at arbitrary angles is considered here, without any restrictive assumption on the values of the involved physical and geometrical parameters. Spectral properties of modes are studied, by deriving generalized conditions for establishing the proper or improper nature of the spatial harmonics in the Floquet representation of the fields. The proposed approach, based on a full-wave moment-method discretization of the relevant electric-field integral equation in the spectral domain, is validated through comparisons with the available data in the literature. Novel results are presented which illustrate the continuous evolution of modes as a function of the propagation angle along the grating, both in surface and leaky propagation regimes.