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Generalized Lorentz-Lorenz formulas are developed for the effective parameters of binary lattice metamaterials composed of a periodic arrangement of electric and/or magnetic inclusions. The proposed homogenization approach is based on a dual dipole approximation for the induced currents. The obtained formulas for the metamaterial effective electric and magnetic characteristics duly consider both electric and magnetic polarizabilities of the inclusions and completely describe the effects of frequency and spatial dispersion. Several numerical examples are provided to demonstrate the general applicability of the proposed formulas to different types of binary lattices and inclusions. It is shown that the proposed effective parameters have the capability of providing a physically sound and accurate description of wave propagation in the metamaterials in an extended range of frequencies in contrast to the equivalent parameters that can be defined in the absence of impressed sources and assuming a local anisotropic constitutive model, which hides inherent spatial dispersion effects and nonphysical features. To gain further insight into the metamaterial response and the physical meaningfulness of calculated effective parameters, the power flow of metamaterial supported modes is analyzed and its homogenized representation is compared to the complete description. A correspondence between the power flow due to the microscopic field and the effect of spatial dispersion in the homogenized parameters is established.

We employ the generalized Lorentz-Lorenz method to investigate how both magnetoelectric coupling and spatial dispersion influence the artificial magnetic capabilities at terahertz frequencies of the representative case of a metamaterial consisting of a three-dimensional (3D) lattice of TiO2 microspheres. The complex wavenumber dispersion relations pertaining to modes supported by the array, traveling along one of the principal axes of the array with electric or magnetic field polarized transversely and longitudinally (with respect to the mode traveling direction), are studied and thoroughly characterized. One mode with transverse polarization is dominant at any given frequency for the analyzed dimensions, proving that the 3D lattice can be treated as a homogeneous medium with defined electromagnetic material parameters. We show, however, that bianisotropy is a direct consequence of magnetoelectric coupling, and the dyadic expressions of both effective and equivalent material parameters are derived. In particular, we analyze the effect of spatial dispersion on the effective parameters relative to a composite material made by a 3D lattice of TiO2 microspheres with filling fraction around 30% and near the first Mie magnetic dipolar resonance. Finally, we homogenize the metamaterial in terms of equivalent index and impedance, and by comparison with full-wave simulations, we explain the presence of the unphysical antiresonance permittivity behavior observed in previous work. © 2014 Optical Society of America.

We introduce our solution for the diffraction of a pulsed ray field, with spherical wavefront, by the vertex (tip) of a pyramid. Within the Uniform Geometrical Theory of Diffraction (UTD) we improve the time domain (TD) solutions available in the literature by introducing the field diffracted by a perfectly conducting faceted structure made by interconnected flat plates, for source and observation points at finite distance from the tip. The proposed closed form expression for an exciting impulsive source has been calculated by employing the one-sided inverse Fourier transform of the frequency domain solution. The solution obtained is able to compensate for the discontinuities of the field predicted by standard TD-UTD, i.e., time domain geometrical optics (TD-GO) combined with the TD-UTD wedge singly diffracted rays. © 2013 IEEE.

In this work, we study the electromagnetic properties of a metamaterial made by a cubic array of TiO2 microspheres embedded in a host medium at terahertz frequencies. By employing the method reported in [1] by Silveirinha, we are able to consider in the computation the effect of magnetoelectric coupling between TiO2 microspheres, as well as spatial dispersion. After calculation of the dominant mode inside the structure, we show that the effect of spatial dispersion on the effective parameters for this kind of systems is relatively weak. Accuracy of the results and effectiveness of homogenized parameters have been demonstrated by comparison against full-wave simulations for a 5-layer slab of such a metamaterial. © 2013 IEEE.

Metamaterials and plasmonics based on micro- and nanostructured metallic-dielectric composites are bringing an important revolution to the microwave and optics fields due to their potential for enabling the realization of novel physical properties unattainable from natural materials, such as isotropic negative refraction, slow light, near-field enhancement, as well as EM focusing and energy transfer beyond the diffraction limit. Such artificial composite structures owe their peculiar properties both to the constituent materials which comprise their elementary building blocks and to their specific spatial arrangement. The use of homogenization methods can provide a convenient characterization of EM-wave-matter interaction by describing metamaterials as bulk homogeneous materials with effective parameters that take into account their inherent qualities and complex nature. While the concept of homogenization theory is easily applied to the long-wavelength limit, e.g. the microwave regime where true sub-wavelength structures can be fabricated, the optical regime challenges the underlying hypothesis of a true subwavelength unit cell. Indeed, for artificial materials the size of the lattice constant is typically only moderately smaller than the wavelength of light. As a consequence, metamaterials can be characterized by nonnegligible spatial dispersion effects. © 2013 IEEE.

Generalized Lorentz-Lorenz formulas are developed for the effective parameters of metamaterials composed of a periodic arrangement of plasmonic nanoclusters (NCs). Each NC exhibits both electric and magnetic polarizabilities but its dimension is in general not very subwavelength. The obtained formulas for the metamaterial effective electric and magnetic characteristics duly consider both electric and magnetic polarizabilities and naturally describe the effects of frequency and spatial dispersion. Homogenization results for a material considered here show the effects of spatial dispersion near the fundamental electric resonance. © 2013 EurAAP.

We present an equivalent X-shaped lumped circuit network to be interposed in the transmission line (TL) modelling reflection and transmission through a recently proposed metalayer in planar technology. The metalayer consists of arrayed pairs of planar conductors that support two main resonant modes, corresponding to either a symmetric or an antisymmetric current distribution in the pairs. The antisymmetric mode is associated with artificial magnetism. We show that reflection and transmission features of a metalayer are accurately predicted by this simple but effective TL model. We also make a clear distinction for the first time between transmission peaks and resonance frequencies, and their relations are investigated in detail. This paper clearly defines the concept of magnetic resonance and identifies the analytical conditions corresponding to total reflection and transmission through a metalayer made of pairs of conductors supporting symmetric and antisymmetric modes. © 2012 IEEE.

The optical response of irregular spherical nanoclusters (NCs) are studied by Monte Carlo simulations. Deviations from nominal arrangements are considered by introducing either randomly variable sizes of the constituent particles or random displacements of particle locations around the NC core. The impact of disorder on NC resonances is examined by decomposing the scattered fields in terms of contributions of electromagnetic multipoles, such as electric and magnetic dipoles, quadrupoles, and higher order moments. © 2012 IEEE.

We characterize the modes with real and complex wavenumbers for both longitudinal and transverse polarization states (with respect to the mode traveling direction) in three dimensional (3D) periodic arrays of titanium dioxide (TiO2) microspheres in the frequency range between 250 GHz and 350 GHz. Modal results are computed by using a single magnetic dipole approximation (SDA) and an SDA model with correction (SDA-WC) that assumes the array to be embedded in a host with an effective permittivity computed through Maxwell Garnett formulas. Moreover, for the transverse polarization case, modal wavenumbers are computed also by fitting the full-wave simulation magnetic field (one point per unit cell) in a finite thickness structure, and their agreement and disagreement are discussed. The longitudinal polarization is not affected by the artificial correction introduced in the SDA-WC; in the transverse polarization case, instead, the correction is needed to obtain results in better agreement with the full-wave data fit. In the observed frequency range, there are one longitudinal mode and two transverse modes, one forward and one backward, where the forward one is "dominant" (i.e., it contributes mostly to the field in the array). Therefore, in the case of transverse polarization, we describe the composite material in terms of homogenized refractive index and relative permeability, comparing results from (i) modal analysis (with and without correction), (ii) Maxwell Garnett formulas, and (iii) Nicolson-Ross-Weir retrieval method from scattering parameters of finite thickness structures. The agreement among the different methods justifies the performed homogenization procedure in the case of transverse polarization. We show that artificial magnetism is generated from a nonmagnetic composite material. © 2012 Optical Society of America.

We investigate the optical properties of metamaterials formed by collections of three-dimensional clusters of plasmonic nanoparticles. This type of nanoclusters (NCs) consist of spherical constellations of metallic nanospheres arranged around a central dielectric sphere and support collective plasmon modes among which the most relevant are those associated with the induced electric and magnetic dipole resonances. We discuss the effective electric and magnetic polarizabilities of NCs, emphasizing their isotropic properties, and we show that dense packed arrays of NCs can be used to realize metamaterials with negative effective permittivity and permeability, and even negative effective refractive index at visible frequencies. © 2011 IEEE.

Complex optical modes in 3D-periodic arrays of metallic nanospheres are analyzed at optical frequencies for both longitudinal and transversal (with respect to the mode traveling direction) polarization states. Each nanosphere of the array is modeled to act as a single dipole by using the single dipole approximation approach, and the metal permittivity is described by the Drude model. Complex mode dispersion diagrams, the figure of merit and effective refractive index versus frequency are shown and compared with those obtained with Maxwell Garnett homogenization theory. Comparison with effective permittivity retrieved by scattering parameters of finite-thickness structures will be shown during the presentation. © 2011 IEEE.

A rigorous analytical solution for the description of wave dynamics originated at the interface between a homogeneous half-space and a half-space metamaterial made by arrayed plasmonic nanospheres is presented. The solution is cast in terms of an exact analytical representation obtained via a discretized Wiener-Hopf (WH) technique assuming that each metallic nanosphere is described by the single dipole approximation. The solution analytically provides and describes the wave species in the metamaterial half-space, their modal wavenumbers and launching coefficients at the interface. It explicitly satisfies the generalized Ewald-Oseen extinction principle for periodic structures, and it also provides a simple analytical solution for the reflection coefficient from the half-space. The paper presents a new WH formulation for this class of problems for the first time, and describes the analytical solution, which is also tested against a purely numerical technique. While only the case of orthogonal plane wave incidence and isotropic inclusions is considered here, the method can be easily generalized to the oblique incidence and anisotropic constituent (tensorial polarizability) cases. © 2011 Optical Society of America.

In this paper we analyze the propagation through a metamaterial in planar technology recently proposed. The metamaterial basic constituent cell consists of a pair of tightly coupled conductors that supports two main resonance modes corresponding to either a symmetric or an antisymmetric current distribution in the pair. We present an equivalent X-shaped lumped circuit network to be interposed in the transmission line (TL) model of propagation across a metamaterial layer to reproduce its electric and magnetic resonances. We show that reflection and transmission features of a periodic array of dogbone pairs as well as its dispersion diagram are accurately predicted by this simple but effective model. © 2010 IEEE.

Modern nanochemistry has developed efficient techniques to manipulate nanoscale objects with a highly advanced degree of control. Chemically- engineered nanoparticles can be synthesized with a large choice of sizes, shapes, constituent materials and surface coatings, and further assembled spatially into self-assembled structures, either spontaneously or in a directed manner [1]. Advances in particle self-assembly and the quasi unlimited range of nanostructures with controlled architectures and functions available suggest that such assemblies may also provide a simple route to metamaterials at infrared and visible length scales. Indeed, nanochemistry and self-assembly strategies are able to inexpensively produce materials whose inner structure is natively in the right range of sizes for optical and infrared applications and can provide fully three-dimensional (3D) structures, thus opening the way to the fabrication of 3D-metamaterial samples of finite volume of the highest importance to many applications. Such metamaterials may be used, for example, to create 3D homogeneous, isotropic negative index materials (NIMs), with simultaneously negative permittivity and magnetic permeability, cloaking devices or light-based circuits manipulating local optical electric fields rather than the flow of electrons. © 2010 IEEE.

A uniform high-frequency description is presented for vertex (tip) diffraction at the tip of a pyramid, for source and observation points at finite distance from the tip. This provides an effective engineering tool able to describe the field scattered by a perfectly conducting faceted structure made by interconnected flat plates within a uniform theory of diffraction (UTD) framework. Despite the adopted approximation, the proposed closed form expression for the vertex diffracted ray is able to compensate for the discontinuities of the field predicted by standard UTD, i.e., geometrical optics combined with the UTD wedge diffracted rays. The present formulation leads to a uniform first order asymptotic field in all the transition regions of the tip diffracted field. The final analytical expression is cast in a UTD framework by introducing appropriate transition functions containing Generalized Fresnel Integrals. The effectiveness and accuracy of the solution is checked both through analytical limits and by comparison with numerical results provided by a full wave method of moments analysis. © 2009 IEEE.

We present a lumped circuit description of a novel metamaterial layer made of arrayed pairs of tightly coupled conductors (dogbones or Jerusalem crosses). This lumped element network is synthesized to exhibit the same frequency response of the metamaterial layer when inserted in the plane-wave equivalent transmission line. The metamaterial and its transverse equivalent network (TEN) model is then applied to the design of a high impedance surface for low profile dipoles and a partially reflective superstrate for highly directive Fabry-Perot cavity antennas. Numerical results illustrating the radiation properties of such antennas are provided.

A dual band 2-D leaky wave antenna is presented. The antenna is constructed from a double layer partially reflective surface suspended above a metallic ground plane, forming two Fabry Perot cavities corresponding to the two different resonant frequencies. The paper demonstrates the successful operation of the antenna through simulation and measurement. ©2007 IEEE.

Antennas with large gain are obtained here with one or few radiators. The main idea consists of inserting simple radiating elements, as patches, inside a Fabry-Perot Cavity (FPC) resonator. This consists of a ground plane covered by a partially reflecting surface (PRS). We provide here some simple rules for the design of such systems, paying attention to a) the required bandwidth and gain, and b) the equivalent model of the periodic surface that forms the PRS, with the goal of designing large antenna gain by using arrays with thinned number of elements. In the present investigation we obtain 19 dB gain with a 2×2 array with a bandwidth of 3.6%.

A Fabry-Perot cavity (FPC) between a ground plane and a partially reflective surface (PRS) is used here to design array antennas with large distance between the radiating elements. This configuration provides some advantages: i) a reduction of the number of array elements to achieve high directivity; ii) large space between contiguous elements that may host a bulky feeding network as required for dual polarization or active antennas; iii) small coupling and easy feeding network designs because of the smaller number of elements with larger inter-element distance. We show that when designing the FPC antenna a frequency shift of the gain maximum may occur, especially in this sparse array configuration. We also show the existence of preferred distances between elements that controls both the directivity and the side lobe level, and how the presence of the FPC and the relaxed requirement of the interelement distance result in a lower interelement coupling. The presented dual polarized antenna comprises two interleaved 2 × 2 arrays placed in a 2-layer FPC, and exhibits a 19 dBi gain and 30 dB of isolation between the two ports over an operating bandwidth of approximately 5.7%, i.e., typical for patch antennas. © 2006 IEEE.

A superstrate of an EBG material (or equivalently a Fabry-Perot cavity) is used to design array antennas with large distance between the radiating elements. This configuration provides some advantages: i) a reduction of the number of array elements to achieve high directivity; ii) large space between contiguous elements decreases their coupling and permits an easy arrangement for complicated feeding network (as needed for dual polarization), also on the same plane of the radiating elements. These possibilities are clearly shown in a few examples treated here and in the design of dual polarized antennas with two interleaved arrays. Furthermore, we indicate that in these designs there are optimum distances between elements that either maximize the directivity or minimize the side lobe level. It is also shown that due to the fact that the radiating elements have larger-than-usual mutual distances it is easy to achieve -40dB of isolation between the two excitation ports, for the two polarizations. © 2005 IEEE.

This study aims at describing the field propagation in terms of pulsed rays, that are particularly advantageous when dealing with short-pulse excitations. In the framework of the Geometrical Theory of Diffraction we augment Geometrical Optics and uniform singly diffracted field solutions available in the time domain (TD), by TD doubly diffracted (DD) rays, that are expressed in simple closed forms. Impulsive double diffraction at a pair of coplanar edges is here formulated directly in the TD, as a double superposition of impulsive spherical waves. Nonuniform and uniform wavefront approximations for TD-DD fields are determined in closed form, defining two novel TD transition functions. The scalar case with either hard or soft boundary conditions is analyzed first, and then used to build an electromagnetic dyadic DD coefficient for a pair of coplanar edges with perfectly conducting faces. Particular attention is given to the definition of TD transition regions, i.e., the elliptical regions where the TD-DD field does not exhibit a ray optical behavior. The compensation mechanism by which the TD-DD fields repair the discontinuity introduced by singly diffracted fields at their shadow boundaries is also analyzed in detail. Our result for the TD-DD field excited by an impulsive spherical wave is valid only for early times, at and close to (behind) the DD ray wavefront. The TD-DD field response to a more general pulsed excitation is obtained via convolution, and if the exciting signal has no low-frequency components the range of validity of the resulting pulsed response is enlarged to later observation times behind the wavefront. © 2005 IEEE.

A superstrate of an EBG material (or equivalently a Fabry-Perot cavity) is used to design array antennas with large distance between the radiating elements. This configuration provides some advantages: i) a reduction of the number of array elements to achieve high directivity; ii) large space between contiguous elements decreases their coupling and permits an easy arrangement for complicated feeding network (as needed for dual polarization), also on the same plane of the radiating elements. These possibilities are clearly shown in a few examples treated here and in the design of dual polarized antennas with two interleaved arrays. Furthermore, we indicate that in these designs there are optimum distances between elements that either maximize the directivity or minimize the side lobe level. It is also shown that due to the fact that the radiating elements have larger-than-usual mutual distances it is easy to achieve -40dB of isolation between the two excitation ports, for the two polarizations. © 2005 IEEE.

Numerically efficient results for short pulse propagation in a complex environment is presented in terms of multiple diffraction. As such, the time domain (TD) diffraction propagators are based on discretization of a generic short-pulse in terms of narrow rectangles, and on closed form representations of diffracted fields when the excitation is a narrow rectangular pulse.

Double diffraction at a pair of coplanar skew wedges and vertex diffraction at the tip of a pyramid was studied. A new time domain version of the uniform description of the two types of diffraction was presented. Evaluation of the diffracted fields in closed form was performed by waveform approximations.

A time domain version of the uniform description of double diffraction at a pair of coplanar skew edges is presented. This description has been derived by direct Fourier inversion of the frequency domain (FD) doubly diffracted (DD) field.

This second part of a two-paper sequence deals with the physical interpretation of the rigorously derived high-frequency asymptotic wave-field solution in Part I, pertaining to a semi-infinite phased array of parallel dipole radiators. The asymptotic solution contains two parts that represent contributions due to truncated Floquet waves (FW's) and to the corresponding edge diffractions, respectively. The phenomenology of the FW-excited diffracted fields is discussed in detail. All possible combinations of propagating (radiating) and evanescent (nonradiating) FW and diffracted contributions are considered. The format is a generalization of the conventional geometrical theory of diffraction (GTD) for smooth truncated aperture distributions to the truncated periodicity-induced FW distributions with their corresponding FW-modulated edge diffractions. Ray paths for propagating diffracted waves are defined according to a generalized Fermât principle, which is also valid by analytic continuation for evanescent diffracted ray fields. The mechanism of uniform compensation for the FW-field discontinuities (across their truncation shadow boundaries) by the diffracted waves is explored for propagating and evanescent FW's, including the cutoff transition from the propagating to the evanescent regime for both the FW and diffracted constituents. Illustrative examples demonstrate: 1) the accuracy and efficiency of the high-frequency algorithm under conditions that involve the various wave processes outlined above and 2) the cogent interpretation of the results in terms of the uniform FW-modulated GTD. ©2000 IEEE.

This two-part sequence deals with the derivation and physical interpretation of a uniform high-frequency solution for the field radiated at finite distance by a planar semi-infinite phased array of parallel elementary electric dipoles. The field obtained by direct summation over the contributions from the individual radiators is restructured into a double series of wavenumber spectral integrals whose asymptotic reduction yields a series encompassing propagating and evanescent Floquet waves (FW's) together with corresponding diffracted rays, which arise from scattering of the FW at the edge of the array. The formal aspects of the solution are treated in the present paper (Part I). They involve a sequence of manipulations in the complex spectral wavenumber planes that prepare the integrands for subsequent efficient and physically incisive asymptotics based on the method of steepest descent. Different species of spectral poles define the various species of propagating and evanescent FW. Their interception by the steepest descent path (SDP) determines the variety of shadow boundaries for the edge truncated FW. The uniform asymptotic reduction of the SDP integrals, performed by the Van der Waerden procedure and yielding a variety of edge-diffracted fields, completes the formal treatment. The companion paper (Part II [1]) deals with the phenomenology of these local diffracted waves based on the present formal solution. The phenomenology encompasses all possible contributions of propagating and evanescent edge diffractions excited by propagating and evanescent FW's. The outcome is a physically appealing and accurate high-frequency algorithm, which is numerically efficient due to the rapid convergence of both the FW series and the series of relevant diffracted fields. This is demonstrated by numerical examples for radiation from a strip array in Part II. ©2000 IEEE.

This second part of a two-paper sequence deals with the physical interpretation of the rigorously derived high-frequency asymptotic wave-field solution in Part I, pertaining to a semi-infinite phased array of parallel dipole radiators. The asymptotic solution contains two parts that represent contributions due to truncated Floquet waves (FW's) and to the corresponding edge diffractions, respectively. The phenomenology of the FW-excited diffracted fields is discussed in detail. All possible combinations of propagating (radiating) and evanescent (nonradiating) FW and diffracted contributions are considered. The format is a generalization of the conventional geometrical theory of diffraction (GTD) for smooth truncated aperture distributions to the truncated periodicity-induced FW distributions with their corresponding FW-modulated edge diffractions. Ray paths for propagating diffracted waves are defined according to a generalized Fermât principle, which is also valid by analytic continuation for evanescent diffracted ray fields. The mechanism of uniform compensation for the FW-field discontinuities (across their truncation shadow boundaries) by the diffracted waves is explored for propagating and evanescent FW's, including the cutoff transition from the propagating to the evanescent regime for both the FW and diffracted constituents. Illustrative examples demonstrate: 1) the accuracy and efficiency of the high-frequency algorithm under conditions that involve the various wave processes outlined above and 2) the cogent interpretation of the results in terms of the uniform FW-modulated GTD. ©2000 IEEE.

This two-part sequence deals with the derivation and physical interpretation of a uniform high-frequency solution for the field radiated at finite distance by a planar semi-infinite phased array of parallel elementary electric dipoles. The field obtained by direct summation over the contributions from the individual radiators is restructured into a double series of wavenumber spectral integrals whose asymptotic reduction yields a series encompassing propagating and evanescent Floquet waves (FW's) together with corresponding diffracted rays, which arise from scattering of the FW at the edge of the array. The formal aspects of the solution are treated in the present paper (Part I). They involve a sequence of manipulations in the complex spectral wavenumber planes that prepare the integrands for subsequent efficient and physically incisive asymptotics based on the method of steepest descent. Different species of spectral poles define the various species of propagating and evanescent FW. Their interception by the steepest descent path (SDP) determines the variety of shadow boundaries for the edge truncated FW. The uniform asymptotic reduction of the SDP integrals, performed by the Van der Waerden procedure and yielding a variety of edge-diffracted fields, completes the formal treatment. The companion paper (Part II [1]) deals with the phenomenology of these local diffracted waves based on the present formal solution. The phenomenology encompasses all possible contributions of propagating and evanescent edge diffractions excited by propagating and evanescent FW's. The outcome is a physically appealing and accurate high-frequency algorithm, which is numerically efficient due to the rapid convergence of both the FW series and the series of relevant diffracted fields. This is demonstrated by numerical examples for radiation from a strip array in Part II. ©2000 IEEE.

Approximate high-frequency expressions for the currents induced on a perfectly conducting plane angular sector are derived on the basis of the incremental theory of diffraction (ITD). These currents are represented in terms of those predicted by physical optics (PO) plus fringe contributions excited by singly and doubly diffracted (DD) rays at the two edges of the angular sector. For each of these two contributions, additional currents associated to vertex diffracted rays are introduced that provide continuity at the relevant shadow boundary lines. The transition region of DD rays is described by a transition function involving cylinder parabolic functions. The asymptotic solution presented here is constructed in such a way to satisfy far from the vertex the expected edge singularities, which tend to be the same as those predicted by the exact solution of the half plane. Numerical results are compared with the exact solution of the same problem and with moments method results for scattering from polygonal plates. © 1998 IEEE.

A uniform high-frequency solution is presented for the field radiated at finite distance by a semi-infinite beamscanning array of magnetic line sources located on a perfectly conducting half-plane. The field is represented in terms of Floquet waves plus their relevant singly and doubly diffracted rays, which arise from both the end of the array and the edge of the half-plane. This representation is uniformly valid also when transition conditions from propagating to evanescent Floquet waves occur. Furthermore, it provides a simple and attractive physical interpretation and is found numerically very effective, due to the fast convergence of the Floquet wave expansion for the field. © 1998 IEEE.

The shielding effectiveness of a corrugated thick screen is theoretically and experimentally investigated. This screen consists of a half-plane of finite thickness in which corrugations are etched on the smaller side. This structure provides a significant attenuation in the shadow region for both polarizations of the incident field; thus, it can be effectively used for protecting apparatuses from radiating interference as well as for decoupling nearby operating antennas. The shielding properties of the screen are described by a high-frequency formulation that involves dosed-form expressions. An experimental setup at X band has been arranged to test the effectiveness of a corrugated screen; the field in the shadow region is compared with that of a screen without corrugations. The experimental results compare very well with those obtained by the high-frequency expressions.

In order to understand and quantify the high-frequency wave processes associated with Floquet wave (FW) edge diffraction, this paper deals with the canonical Green's function of a semiinfinite phased array of dipoles in free space. The diffracted field contributions due to each incident FW field are cast in a dyadic form that highlights the behavior of TE and TM waves. Special attention is given to evanescent diffracted fields, which are associated with high order FWs.

A closed-form high-frequency solution is presented for the near-field scattering by a thick screen illuminated by a line source at a finite distance. This solution is applicable to a thick screen with perfectly conducting side walls and either perfectly conducting or artificially soft boundary conditions on the face joining the two wedges. This latter condition is obtained in practice by etching on that face quarter of a wavelength deep corrugations with a small periodicity with respect to the wavelength. It is shown that the artificially soft surface provides a strong shadowing for both polarizations; thus, it is suggested that such configurations may usefully be employed to obtain an effective shielding from undesired interferences. Several numerical calculations have been carried out and compared with those from a method of moments (MoM) solution for testing the accuracy of our formulation, as well as to demonstrate the effectiveness of the corrugations in shielding arbitrarily polarized incident field. © 1997 IEEE.

A high-frequency solution is presented for the scattering in the near zone by a pair of coplanar skew edges when they are illuminated by a source at a finite distance. The solution is obtained by using a spherical-wave spectral representation of the first-order diffracted field from each edge. The final closedform asymptotic solution includes terms up to the second order. It is shown that this second-order contribution is of the same order as the first one in overlapping transition regions. Moreover, the solution is cast in a convenient form, which is also directly applicable to treat the case when the two edges share a common face for both soft and hard boundary conditions. By choosing appropriate reference systems, the formulation for the scalar case is directly used to construct the solution of the more general electromagnetic problem for an arbitrarily polarized incident field. Numerical results are presented and discussed. © 1997 IEEE.

A Floquet waves (FW) representation is used to efficiently calculate the active free-space Green's function. The representation interprets the radiation of a finite phased array as a superposition of FW distributions on the global aperture of the array. The Green's function of an array of dipoles which is truncated in one dimension and infinite in the other is formulated. The dipoles are considered of uniform amplitude and linearly phased for including a scan beam description. By invoking the locality of the high-frequency phenomena, the actual finite distribution may be treated by using local edges.

Asymptotic, closed form expressions of the fringe currents of the plane angular sector of a plane wave far-field regime are derived using the Incremental Theory of Diffraction (ITD). Numerical results show that ITD is more accurate than the Uniform Theory of Diffraction. A double diffracted field is found to occur at a shadow boundary line equal to 52°.

The problem of edge diffraction close to a point caustic is analyzed in a typical dual-reflector Gregorian antenna in offset configuration. The diffraction phenomenon is produced by a perfectly conducting fin located between the feeder and the main reflector. This fin is sometimes used to reduce the coupling between the primary feed and the main reflector. For the sake of simplicity, the two-dimensional case is studied here, but the present technique can also be applied to practical three-dimensional configurations. © 1997 John Wiley & Sons, Inc.

A closed form, high-frequency solution is presented for the scattering in the near zone by a semi-infinite thick screen, when it is illuminated by a line source at finite distance. This solution is derived for a thick screen with perfectly conducting side walls, and either perfectly conducting or artificially soft boundary condition on the top face joining the two wedges. This last condition is practically obtained by etching on this face a quarter of wavelength deep corrugations with a small periodicity with respect to the wavelength. Owing to the particular properties of the artificially soft surface, a strong decoupling effect in the shadow region is achieved for both polarizations; thus, an effective shielding from undesired interferences is obtained.

A problem of a semi-infinite array of line sources located on a perfectly conducting half-plane has been studied by using a Floquet modes approach. This approach overcomes the slow convergence of the direct summation of the space fields radiated by each element of the array. The formulation presented can be extended to the 3D case.