1,721,137 research outputs found
Advances in Leaky-Wave Periodic Structures after Oliner’s Pioneering Investigations
No full textThe research activity jointly developed during the last decade between the groups coordinated by P. Lampariello in Europe and by D. R. Jackson in the U.S.A. is reviewed, on the basis of the fruitful scientific interaction had with Prof. Oliner since the Eighties. The main focus here is on advances in leaky waves and leaky-wave antennas based on periodic structures. This involves topics of different nature, such as issues of numerical modeling in periodic Green’s functions, leakage features in metamaterials and other innovative media, and onedimensional and two-dimensional configurations of printed and planar leaky-wave radiators.The research activity jointly developed during the last decade between the groups coordinated by P. Lampariello in Europe and by D. R. Jackson in the U.S.A. is reviewed, on the basis of the fruitful scientific interaction had with Prof. Oliner since the Eighties. The main focus here is on advances in leaky waves and leaky-wave antennas based on periodic structures. This involves topics of different nature, such as issues of numerical modeling in periodic Green’s functions, leakage features in metamaterials and other innovative media, and onedimensional and two-dimensional configurations of printed and planar leaky-wave radiators
Closed-form analysis of dispersive properties for multilayered waveguiding structures
No full textVarious dispersive properties of arbitrary multilayered waveguiding lossless structures are stated, generalizing what is already known for basic single slabs. These features enable us to derive simple but rigorous closed-form expressions for the calculation of the number of propagating surface waves; these expressions are also useful for an effective location of the relevant cutoff frequencies. The proposed analysis for the fundamental modal characterization of multilayered structures in terms of their physical and geometrical parameters allows one to avoid an often complicated numerical search for the solution of typical transcendental equations. © 2010 EuMA
Leaky-wave radiation at broadside from one-dimensional open periodic structures
No full textRadiation at broadside from leaky waves is studied for one-dimensional periodic structures modeled by means of a transmission line periodically loaded by series or shunt loads. An asymptotic Bloch analysis of the equivalent network and a simple array-factor calculation of the radiated far field allows the derivation of conditions for achieving maximum power density radiated at broadside and beam splitting in terms of the dispersion properties of the corresponding leaky mode. The 3 dB frequency bandwidth for broadside radiation is characterized in terms of the leaky-pole locations in the complex plane and an approximate formula is provided. © 2005 IEEE
Analysis and optimization of radiation at broadside from a class of 1D periodic structures
No full textRadiation at broadside from leaky waves is studied for one-dimensional periodic structures modeled by means of a transmission line periodically loaded by series or shunt loads. Radiation at broadside occurs via an axially fast spatial harmonic in a neighborhood of the open-stopband frequency; operation in such a frequency range is studied here by means of an approximate asymptotic Bloch analysis of the adopted equivalent network and a simple array-factor calculation of the radiated far field. The condition of equal values for the phase and attenuation constants of the radiating spatial harmonic is shown to give rise to maximum radiation at broadside in the lossless case and to the splitting of a single peak of the radiation pattern at broadside into two distinct peaks in both the lossless and the lossy cases. The 3 dB frequency band for broadside radiation is characterized in terms of the leaky-pole locations in the complex plane and an approximate formula for the antenna bandwidth is provided. Numerical results illustrating these properties are provided, including full-wave simulations of a specific structure through the method of moments
Fundamental properties of surface waves in lossless stratified structures
No full textThis 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
Integral representations of the 1D periodic layered-media Green’s function for periodic printed leaky-wave antennas
No full textAn investigation on radiation at broadside from leaky plasmon waves on periodic structures
No full textFundamental properties and optimization of broadside radiation from uniform leaky-wave antennas
No full textIn this paper, radiation at broadside is studied for a general class of leaky-wave antennas (LWAs) comprised of a grounded slab covered with a partially reflecting surface, on the basis of a simple transverse equivalent network model of the structure. The analysis of the one-dimensional (1-D) version of such a LWA excited by a line source shows that a central role in establishing the features of broadside radiation is played by the condition that the phase and attenuation constants of the leaky mode responsible for radiation are equal. When this happens, a beam with a single peak at broadside is on the verge of splitting into two distinct peaks, and maximum power density is radiated at broadside. Design formulas to achieve such an optimized condition, as well as approximate expressions for the frequency bandwidth and pattern beamwidth of the antenna and for the leaky-wave phase and attenuation constants are derived, both in the absence and in the presence of losses; in addition, an optimal-beamwidth condition (which gives the narrowest broadside beam) is derived. Finally, all the results are extended to the practical case of a 2-D LWA excited by a horizontal dipole
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