P. Lampariello

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.

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.

A Novel Phased Array of Printed-Circuit Leaky-Wave Line Sources

A novel linear phased array of parallel leaky-wave line sources is proposed and analyzed that furnishes a two-dimensional scan within a certain sector in space by frequency or electronic scan in elevation and phased scan in azimuth. The line sources themselves are new, being printed-circuit versions of the offset-groove-guide leaky-wave antenna. The complete antenna is analyzed very accurately, taking into account all mutual coupling effects, by using a new tee network in a transverse resonance procedure. The antenna is notable for having no cross polarization, no blind spots, and no grating lobes.

New equivalent networks with simple closed-form expressions for open and slit-coupled E-plane tee junctions

Analytical expressions are presented for the elements of new equivalent networks for open and slit-coupled E-plane tee junctions. The expressions are in simple closed form, and their accuracy is verified by comparisons with measurements. Physically based stored power considerations are also developed in context to indicate how appropriate changes in the geometry can be taken into account. >

Attractive features of leaky-wave antennas based on ferrite-loaded open waveguides

A complete investigation is presented as regards the performances of a class of leaky-wave antennas which are electronically scannable by varying either frequency or magnetization. The basic topology is derivable from that one of a laterally-open rectangular guide, loaded with a transversely-magnetized ferrite rod. It is seen that the characterization of the radiation properties may suitably be achieved by considering a leaky-wave approach also for this kind of structure. A parametric analysis is then developed, based on an innovative transverse resonance technique, expressly extended to nonreciprocal structures. The phase and leakage constants are derived as functions of the involved physical quantities, thus identifying immediately those conditions that may really be useful in the applications. The relevant radiation patterns are then computed with both rigorous and approximate techniques. It is finally shown that, even with simple isotropic sources, such a topology can present various interesting distinctive features (structural simplicity, wide forward/backward angular beam scannings, etc.).

Guidance and Leakage Properties of Offset Groove Guide

A new leaky-wave structure, the offset groove guide, is analyzed accurately by two completely different methods: a novel tee-junction equivalent network approach and a numerical mode-matching procedure. The new structure is discussed first, and it is then shown that the numerical values for the propagation characteristics obtained by each method agree very well with each other, When the offset metal walls are finite in height, an unexpected additional set of leaky modes is present that can couple to the expected offset-groove-guide leaky mode and produce quite complicated but interesting modal behavior. This behavior is discussed as a function of offset and wall height.

A versatile leaky-wave antenna based on stub-loaded rectangular waveguide .III. Comparisons with measurements

For pt.II ibid., vol.46, no.7, p.1042-46. The article describes the measurements that verify the validity of the theoretical expressions for this new type of antenna. Measurements were made both at millimeter wavelengths (40 to 60 GHz) and in the X-band (8 to 12 GHz) frequency range and of two different quantities: the propagation wavenumbers /spl beta/ and /spl alpha/ and radiation patterns. Comparisons were made with numerical values obtained from the theoretical expressions derived in parts I and II and very good agreement was found in all cases.