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The goal of this paper is to overview radio-frequency (RF) electromagnetic interactions with solid and liquid materials from the macroscale to the nanoscale. The overview is geared toward the general [...]

Light is an etectromagnetic wave composed of oscillating electric and magnetic fields, the one never occurring without the other. In tight-matter interactions at optical frequencies, the magnetic component of light generally plays a negligible role. When we 'see' or detect tight, only its electric field is perceived; we are practically blind to its magnetic component. We used concepts from the field of metamaterials to probe the magnetic field of light with an engineered near-field aperture probe. We visualized with subwavelength resolution the magnetic- and electric-field distribution of propagating tight. 10.1126/science.1177096

A whistler wave in a cavity filled with a magneto-plasma medium is strongly affected when the plasma source is switched-off. Due to such a collapse of the plasma, the whistler wave is converted to an electric- field-intensified higher frequency wave (with an order of magnitude upshift of the frequency). In principle, it is possible to transform a 2.45 GHz source radiation to 300 GHz Terahertz radiation, with significant strength of the electric field. Finite difference time domain (FDTD) technique is used to study the effect of the following parameters: the rate of collapse, spatial plasma-density profile, collision frequency as well as the switching angle. Index Terms--Cavity, finite difference time domain (FDTD), frequency transformer, time-varying medium, whistler wave.

Optimal spectral sampling (OSS) is a computationally fast and accurate method for modeling sensor-band transmittances and radiances. The spectral response of a sensor channel is approximated by an optimally weighted average of monochromatic radiative transfer calculations at optimally selected points. The absorption coefficients for the selected points are obtained from prestored lookup tables. Analytical Jacobians are produced in conjunction with the radiances with very little added computational burden. A microwave version of the OSS training algorithm and forward model has been developed in parallel with the infrared version. The microwave model treats [O.sub.2] and [N.sub.2] as fixed gases and [H.sub.2]O and [O.sub.3] as variable gases. Several reference line-by-line (LBL) models are available for training. The method of tabulating and interpolating absorption coefficients has been optimized for execution speed. Results are shown for OSS application to several current and future microwave sounders. With a selected requirement of 0.05-K rms error (with respect to the reference LBL model), the number of monochromatic points required varies from one, for most window channels, to about four for channels embedded in the 60-GHz [O.sub.2] line complex and along the 183-GHz [H.sub.2]O line. Even in the cases where a single point is adequate, the optimal point does not necessarily coincide with the center frequency of the channel. Index Terms--Electromagnetic propagation in absorbing media, radiative transfer modeling, terrestrial atmosphere.

A full 3D hybrid method for analyzing electromagnetic wave propagation in buildings with realistic wall types and structures is presented. This hybrid method combines full-wave techniques which are used for the analysis of one unit cell of inhomogeneous periodic walls with a ray-tracing-like field calculation for the interaction between the walls. Consequently, the method can overcome the inadequacy of traditional ray-tracing in the presence of inhomogeneous periodic wall structures like cinderblock, rebar structure, etc. but is still computationally tractable. Because of this, both indoor wireless channel characterizations and signal fading statistics are shown to be more accurate with this method. Numerical results of the hybrid method are presented for two simple scenarios and validated with theory and measurement. Furthermore, numerical results for a realistic indoor scene are given and compared to a scene where the periodic walls are replaced with effective homogeneous walls. For both setups, the propagation channel is characterized, fast fading signal statistics are extracted and the inadequacies of the homogeneous wall implementation are pointed out. Index Terms--Indoor propagation, ray-tracing, wireless channel.

The bidirectional analytic ray tracing (BART) method is developed to rapidly calculate composite scattering from three-dimensional (3D) electrically large complex targets above a randomly rough surface. Ray tracing is carried out both along the incident (forward) direction and converse direction of scattering (backward) recording different orders of ray illumination on each facet or edge of the target and surface. Once a pair of forward and backward rays meet on a facet/edge, a scattering term is constructed using the diffused scattering/diffraction of this facet/edge and all reflections occurred on the tracing paths. The rough surface is modeled with 'rough facets' including coherent scattering and diffused incoherent scattering, which can be directly calculated according to the IEM (integral equation method) of a randomly rough surface. Analytic tracing of polygon ray tubes is developed to precisely calculate the illumination and shadowing of facets, which exempt large patches of the target from any finer meshing. It significantly reduces the complexity relevant to the target electric-size. Higher orders of scattering and, in particular, interactions between the target and rough surface are then taken into account. The accuracy and performance of BART is validated and evaluated by comparing with exact computational electromagnetic methods for electrically small targets. Numerical examples of angularly composite scattering from a three-dimensional electrically large, e.g., a ship-like target over a randomly rough surface are presented and discussed. Index Terms--Bidirectional analytic ray tracing (BART), radar cross section (RCS) prediction, target and rough surface.

A novel marching on in time and Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT)-based time domain integral equation solver for analyzing transient scattering from composite multiregion structures comprising homogeneous penetrable volumes and perfectly conducting surfaces is presented. To render the marching on in time procedure stable, observer and source integrals are approximated via multipoint collocation and evaluated in closed form. The proposed scheme avoids the costly evaluation of five dimensional integrals required in full space-time Galerkin schemes, and proves to be stable for all targets investigated, including coated perfect electrically conducting surfaces and multiregion penetrable volumes. Index Terms--Closed-form evaluation, composite, exact evaluation, integral equations, transient.

We present an analytical formula for the radiation resistance of planar short monopole antennas. The linear element of the antenna is placed parallel to a ground plane, extending beyond its edge. The approach, based on the solution for scattering of a plane wave impinging on a perfectly conducting half-plane, uses a combination of the reciprocity theorem, Fresnel integral approximation, and Poynting theorem to derive an analytical expression for the radiation resistance of such monopoles shorter than about [lambda]/10. The analytical results are in very good agreement with measurements and numerical simulation results carried out for a large and finite-size ground plane. It is found that the short planar monopole shows a radiation resistance that has a dominant term depending linearly--instead of quadratically--on the monopole height, thus providing relatively high values for quite short lengths. The same methodology is also applied to the case of a planar short dipole parallel to the half-plane's edge. However, a much lower radiation resistance is obtained in that case. The impact of these results on bent planar monopole designs is briefly discussed. Index Terms--Perfectly conducting half-plane, planar antenna, radiation resistance, short dipole, short monopole.

Creeping wave modes on smooth structures are of importance in the control of scattering properties, such as radar cross section of such structures. We have shown a novel procedure to examine the excitation of creeping wave modes by plane wave illumination of a perfectly electrically conducting (PEC) cylinder. Detailed information about transients of creeping wave modes and their spatial structure, have been obtained for the first time using Singular Value decomposition (SVD) analysis of 3-D Finite Difference Time Domain (FDTD) data. The transient analysis shows how the amplitudes of different modes vary in time, and how the dominant modes eventually stabilize to the time-harmonic solution given by analytical methods. Although the method is computationally expensive, this technique will be particularly useful for purely transient signals, complex geometries and situations involving spatially-varying material properties such as a plasma shielded object. Index Terms--Creeping wave, electromagnetic wave, FDTD, RCS, SVD, UWB.

The behavior of an electromagnetic wave impinging on a thin layer of arbitrary material can be described with a vector circuit interpretation of a transition matrix model. This paper follows the idea of applying such a matrix to the finit-element method (FEM). Especially, several very thin layers composed to an electrically not so thin layer may be treated comfortably. The method will be tested firstly on simple dielectric layer with a known analytic solution. In consequence, the example of a thick layer modeled by a number of thin layers will be given, as well. Index Terms--Bluetooth, coupled network boundary conditions, finite elements, thin layer, transition matrix.

To make plausible the idea that light exerts a pressure on matter, some introductory physics texts consider the force exerted by an electromagnetic wave on an electron. The argument as presented is mathematically incorrect and has several serious conceptual difficulties without obvious resolution at the classical, yet alone introductory, level. We discuss these difficulties and propose an alternative argument. [DOI: 10.1119/1.3027432]

Turbulence properties of communication links (optical and microwave) in terms of log-amplitude variance are studied on the basis of a three-layer model of refractive index fluctuation spectrum in the free atmosphere. We suggest a model of turbulence spectra (Kolmogorov and non-Kolmogorov) changing with altitude on the basis of obtained experimental and theoretical data for turbulence profile in the troposphere and lower stratosphere. OCIS codes: 010.1330, 010.1300.

The leakage of electromagnetic waves and high frequency surges caused by the partial discharge inside gas insulated switchgear (GIS) to the outside of its tank may become a signal for the partial discharge detection, and, on the other hand, possibly cause electromagnetic interference (EMI) to electronic equipment via the grounded system. It is, therefore, important to investigate and understand the leakage phenomenon of electromagnetic waves and high frequency surges to the grounded system of the GIS. In the present study, experiments of the characteristics of leaking electromagnetic waves and high frequency surges were conducted using test models for the cable connections, the disconnecting switch (DS), the earth switch (ES), the capacity type potential divider (PD) inside the GIS, and the grounding wire to clarify the characteristics of the respective elements. These results could be approximated using distributed parameter circuits, and models for the leakage surge analysis were proposed. Index Terms--Gas insulated switchgear (GIS), leaking electromagnetic waves, high frequency surges, cable connections, disconnecting switch (DS), earth switch (ES), capacity type potential divider (PD), grounding wire, framework, EMI.

A time integration scheme is described for simulations of electromagnetic waves within a fully saturated ferrite medium. By considering Maxwell's equations in conjunction with the torque equation of motion for electron precession, we show that a stable second-order scheme can be achieved using both central differences and averages. The scheme is validated using a stripline phase shifter as a test case. Not only does the simulation agree quite well with results produced by a popular frequency-domain, finite element solver, the data also exhibits a very desirable, low-loss, phase shift effect. Index Terms--Ferrite phase shifters, ferrites, finite-difference time-do-main (FDTD), magnetic materials.

In recent years it has been shown that ray propagation in two-dimensional (2D) uniform random percolation lattices is well approximated by stochastic processes. Two of the probabilistic interpretations can be solved exactly but impose some additional restrictions on the ray dynamics: the 1999 model by G. Franceschetti et al. demands that ray reflections inside the lattice are independent and identically distributed (IID); and the 2006 model by A. Martini et al. assumes that for the analysis of vertical ray penetration reflections on vertical lattice cell faces can be neglected. In this paper we present a 2D generalization of the 1999 model that does not rely on the IID assumption. It is based on a set of coupled iteration formulas for right stochastic matrices that describe a time-inhomogeneous Markov process. Upon expanding the space of transition states, the iterative process can be recast in the projection of a time-homogeneous Markov chain. Thus the Perron-Frobenius theorem can be applied to analyze the stationary states of the process, which leads to a simple analytical expression for the probability of a ray ensemble reaching a specified lattice level after infinitely many reflections. We discuss different boundary conditions at the absorbing barriers of the ray propagation process and show that 1) by imposing the IID assumption, the 1999 model by G. Francescetti et al. can be recovered; and 2) a one-dimensional reduction of the approach exactly leads to the 2006 model by A. Martini et al. The presented stochastic approach provides a framework in which basic assumptions of probabilistic interpretations of percolation theory based ray propagation can be studied in some detail. It also allows for the consistent derivation of the stationary probability states which are needed to apply the approach to a wider range of phenomena such as internal-source ray propagation in both uniform and nonuniform random media. Index Terms--Electromagnetic propagation in random media, Markov processes, martingales, mobile communication, urban areas.

In this paper, a novel distributed small-signal heterojunction bipolar transistor (HBT) model at millimeter-wave frequencies is proposed. This new approach integrates the electromagnetic (EM) simulation of the outer extrinsic passive part of an HBT, the coupled transmission lines for the fingers, and the Gupta multiport connection into an efficient global distributed modeling approach. For the first time, the values of the entire HBT intrinsic model elements used in the active elementary cells (AECs) can subsequently be extracted through the explicit analytical expressions derived through the multiport connection method. Good agreement between the measured and the simulated results has been demonstrated. This model has several unique advantages for microwave transistor optimization and synthesis in that the derived explicit analytical expressions are in terms of the effect of the extrinsic parts, allowing the designer to have better control over the whole transistor design. Furthermore, it serves as one of the valuable steps toward global modeling of millimeter-wave devices and circuits. Index Terms--Distributed model, electromagnetic (EM) simulation, global modeling, heterojunction bipolar transistor (HBT), small-signal model.

A new approach for the scattering of electromagnetic (EM) waves from periodic dielectric rough surfaces is addressed. The method is an extension of the buried object approach (BOA), which is developed for rough surfaces of infinite extend, to the present problem. The BOA allows to model the original problem as the scattering of EM waves from cylindrical objects located in a two-half-space medium with planar interface. Then, the problem is reduced to the solution of a Fredholm integral equation of second kind through the periodic Green's function of two-half-space medium. The periodic Green's function of two-half-space medium is calculated via the Floquet mode expansion, whose numerical evaluation can be accelerated by using effective methods. The method can also be used to solve the scattering problems of rough surfaces of infinite extend and having a localized roughness. Numerical simulations show that the method yields effective and accurate results for surfaces of arbitrary variation. Index Terms--Layered media, periodic rough surface, scattering.

A formulation of the Method of Moments (MoM) impedance matrix is presented that facilitates discussion of the behavior of its eigenvalues and eigenvectors. This provides insight into the difficulties of producing iterative solutions to electromagnetic radiation problems, which typically involve nonuniform meshes. Based on this analysis, a localized self-box inclusion (SBI) preconditioner is developed to overcome the aforementioned issues. Numerical results are shown using a parallel multilevel fast multipole algorithm (MLFMA) library, coupled with an implementation of the SBI preconditioner. Using these parallel libraries allows the solution of very large problems, due to both excessive size and poor conditioning. A model of an XM antenna, mounted atop an automobile above a very large ground plane, establishes the effectiveness of these methods for more than 3.5 million unknowns. Index Terms--Electromagnetic radiation, fast solvers, iterative methods, moment methods, preconditioner.

A domain decomposition method is presented for analyzing electromagnetic problems involving multiple separable scatterers. The method first decomposes the original problem into several disjoint subregions. In each subregion, the domain decomposition method is further applied by decomposing the region into smaller, possibly repeated, subdomains. The domain decomposition method is general enough for arbitrary geometries, but is also capable of exploiting repetitions. This renders geometrically complicated and electrically large subregion problems tractable. The subregions communicate through the near-field Green's function. To overcome the vast computational costs required in exchanging information between electrically large subregions, the adaptive cross approximation algorithm is adopted to expedite the process. The method is applied to study radiation characteristics of a reflector antenna system and an antenna array in the presence of a frequency selective surface to demonstrate the utility of the present approach. Index Terms--Adaptive cross approximation (ACA) algorithm, domain decomposition method (DDM), hybrid numerical methods, multiple scattering problems.

High frequency surges leaking through the insulated joint of a GIS were measured, using a model GIS, and the phenomena, characteristics and mechanism were clarified based on the experiment and the circuit theory. High frequency surges decrease the impedance of the insulated joint, producing an almost short circuit state, and the coefficient for refraction from the inside of the GIS tank to the grounding system becomes significantly small. In a multi-phase GIS, surges leaking through the insulated joint form the tank-to-tank mode voltage for the different phase tank, generating the voltage equal to the potential of the voltage application tank to ground. On the other hand, no potential to ground is directly generated to the adjoining bus. The amplitude and the frequency of surges leaking through the insulated joint of a GIS bus are almost identical to those calculated from the distributed constant circuit theory. The phenomena can be, therefore, reproduced using the EMTP through the simulation of the line part by the multi-phase distributed constant and the simulation of the insulated joint by the capacitance. Index Terms--Gas insulated switchgear (GIS), leaking electromagnetic waves, high frequency surges, insulated joint, EMI, EMTP.

The quality factor is analyzed for the spherical modes which represent fields of an antenna in an electrically lossy medium. Like the previous approach in free space, the stored energy in the evanescent field is represented by subtracting the energy associated with the radiation field from the total field energy, instead of evaluating the stored energy over the whole space, simple equations on Q using the radiation efficiency and the medium property are derived using the concept of power dissipation in a lossy medium and the relation between Q of TM and TE modes. The theory is verified by the comparison of Q's evaluated from the impedance band-widths of TM and TE modes and the proposed equations in a lossy medium. Index Terms--Antenna theory, lossy systems, quality factor, spherical mode, stored energy.

A novel antenna is composed of a conical monopole with metallic parasitic elements and a capacitive disk placed above a ground plane. A dielectric substrate is used in order to optimize the performances. This antenna provides broadband characteristics and omnidirectional radiation patterns over the whole bandwidth with a height limited to a one eighth wavelength associated to the lowest frequency. Simulations and experiments demonstrate that this structure exhibits a 2.9:1 impedance bandwidth with VSWR below 2:1 and very good radiation patterns and gain in spite of a size extremely reduced. Index Terms--Broadband antenna, conical monopolar antenna, impedance matching, omnidirectional radiation patterns.

There has been a considerable interest in the use of lower frequency (VHF/UHF) space-based synthetic aperture radar (SAR) for realizing the foliage and ground penetration. The phase perturbation, signal distortion and imaging resolution degradation by the ionosphere will be particularly severe, however the model is not yet well established and still needs to be further studied. In this paper, on the basis of possible improvements for the model proposed by Ishimaru and others, potential ionospheric effects on SAR imaging are evaluated. First, for analyzing azimuthal resolution, we apply the fourth moment recently obtained in general case of strong fluctuation regimes, which is expected to give results for wider conditions. The Gaussian approximation was used in the previous model: however it is only valid in the fully saturated regimes. Second, for analyzing image shift and distortion, besides group delay, the higher-order dispersion is considered. Third, for discussing range resolution degraded due to pulse broadening, besides the dispersion, the multiple scattering of ionospheric turbulence is studied. Fourth, the Faraday rotation effect is analyzed. Numerical simulations are shown using ionospheric turbulence spectrum and TEC inferred from the International Reference Ionosphere (IRI) and satellite beacon observations. Index Terms--Electromagnetic propagation in random media, ionospheric electromagnetic propagation, synthetic aperture radar (SAR).

Electromagnetic creeping waves on a 3-dimensional surface with an anisotropic impedance boundary condition are considered. The influence of the impedance is examined. The standard asymptotic formula for the creeping waves contains the factor 1/([tau]--[q.sup.2]) where [tau] is the attenuation parameter and q is the Fock parameter which depends on the impedance matrix. Analysis of the equation for the attenuation parameter which describes its dependence on q shows that there exist such critical values of q when the factor 1/([tau]--[q.sup.2]) diverges and the usual asymptotic formula gives infinite result. The equation for the critical values of the parameter q is derived and the 4 first critical values are found numerically. The new local asymptotics valid in domain of the size [k.sup.-2/9] (where k is the wave number) is derived in the supposition that the divergence takes place on a curve crossed by creeping waves. This new asymptotic decomposition is carried out by powers of the small parameter [k.sup.-1/9]. The effect of creeping wave passing through the line where the usual asymptotics diverges is examined. Index Terms--Boundary layer, creeping waves, degeneration, electromagnetic propagation, high frequency asymptotics, impedance.

This paper considers the use of a spherical array of sources producing a large fast-transient electromagnetic wave near the center of a sphere. For comparison, a lens type of implosion impulse radiating antenna (IRA) is included as an appendix. This complements the prolate-spheroidal focusing-reflector type of IRA, which has been already appearing in journal papers. Index Terms--Array, electromagnetic implosion, focusing, lens, time domain.

The interaction of the fast cyclotron wave of a linear electron beam guided by a magnetic field with a counter-propagating electromagnetic wave leads to the appearance of a stop-band over a wide range of the magnetic field near its resonance. Suppression of generation in backward wave oscillators and the resonant-cyclotron method of mode selection are based on this effect, termed 'cyclotron absorption.' In this paper, we analyze the possibility of controlling regenerative amplification in such oscillators as a traveling wave tube (TWT) by suppressing parasitic feedback using the guide magnetic field in the region of cyclotron absorption (RCA). Approaching the magnetic field to values that border this region, which contain thresholds of self-excitation, leads to a decrease in suppression of the reflected wave that is responsible for the positive feedback; in other words, this leads to an increase in gain. We illustrate amplification in the RCA using two approaches: the theory of stationary operation of a TWT accounting for the cyclotron resonance of electrons with a reflected wave, and particle-in-cell computer simulations. Index Terms--Cherenkov and cyclotron interactions, cyclotron absorption, cyclotron waves, positive feedback, regenerative amplification, traveling wave tube.

Because of their high stopping power ([X.sub.0] = 1.14 cm, [R.sub.Moliere] = 2.07 cm) and fast (~ 40 ns) bright (4 times of BGO) scintillation, cerium doped lutetium oxyorthosilicate (LSO) and cerium doped lutetium-yttrium oxyorthosilicate (LYSO) crystals have attracted a broad interest in the high energy physics community. This paper presents a comparative study on emission spectra measured for large size BGO, lead tungstate (PbW[O.sub.4]), LSO and LYSO samples excited by UV light (photo-luminescence) with and without internal absorption, x-ray (x-luminescence) and [gamma]-ray (radio-luminescence). A red shift was observed between the emission spectra with internal absorption as compared to that without. An additional red shift and a significant red component were observed in the radio-luminescence spectra measured for LSO samples but not LYSO samples, which were disappeared after a [gamma]-ray irradiation with an accumulated dose of 5 x [10.sup.3] rad. This is the only significant difference observed between the large size LSO and LYSO samples. The origin of these red shifts and the consequence to their light output and applications in the high energy and nuclear physics experiments are discussed. Index Terms--Crystal, lutetium oxyorthosilicate, lutetium yttrium oxyorthosilicate, photo-luminescence, radio-luminescence, scintillator, X-luminescence.

Leaky modes of multilayered substrates play an important role in efficient numerical electromagnetic solvers. In this paper, the location of the propagation constants of the transverse electric and transverse magnetic leaky modes are determined in an efficient way for multilayered substrates with commensurable layer thicknesses. It is shown that, for all practical applications, accurate quasi-static approximations for high mode orders can be derived rapidly by finding the roots of an analytically obtained polynomial. Furthermore, simple closed-form expressions are derived for some particular cases. Starting from these estimates, only a few additional Newton steps are required for a very precise determination of the propagation constants. The proposed method is validated by means of several illustrative numerical examples. Index Terms--Leaky waves, multilayered substrates, numerical electromagnetic analysis, quasi-static approximations.

A modified method of moments/physical optics (MoM-PO) hybrid method is proposed for modelling the radiation of arbitrary wire antennas near to dielectric coated metallic plates. The contribution of the surface wave is taken into account by adding modified factors into the PO operator of the traditional MoM-PO. The discrete complex image method (DCIM) is used to replace the PO operator when the observation point is close to the antenna, since the PO and the asymptotic solutions of surface wave all fail in this region. Several examples are given in this paper to prove the validity of the modified method. Index Terms--Coated plate, discrete complex image method (DCIM), method of moments/physical optics (MoM-PO) hybrid method, surface wave.

Floquet wave and element-by-element summation representations are implemented to investigate the radiation from a periodic, rectangular array of linearly phased/sequentially pulsed dipoles in the frequency-and time-domains. A synthetic aperture type formulation for Floquet wave representation and an asymptotic formulation for the element-by-element summation representation are developed. Numerical results are presented to demonstrate the efficiency of the Floquet wave representation in terms of radiating, non-radiating and diffracted wave constituents and then validated via comparison with direct summation over the contributions of individual dipole radiations. Index Terms--Floquet waves, frequency- and time-domain Green's functions, periodic arrays, phased array antennas, Poisson summation, synthetic aperture, tip diffracted waves.

Simple analytical formulas are introduced for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays of metal strips or square patches over ground planes. Emphasis is on the oblique-incidence excitation. The approach is based on the known analytical models for strip grids combined with the approximate Babinet principle for planar grids located at a dielectric interface. Analytical expressions for the surface impedance and reflection coefficient resulting from our analysis are thoroughly verified by full-wave simulations and compared with available data in open literature for particular cases. The results can be used in the design of various antennas and microwave or millimeter wave devices which use artificial impedance surfaces and artificial magnetic conductors (reflect-array antennas, tunable phase shifters, etc.), as well as for the derivation of accurate higher-order impedance boundary conditions for artificial (high-) impedance surfaces. As an example, the propagation properties of surface waves along the high-impedance surfaces are studied. Index Terms--Analytical model, high impedance surface, oblique incidence excitation.

A novel compact electromagnetic band-gap (EBG) structure in a spiral shape is presented and investigated. This structure significantly enlarges the capacitance between neighboring elements. The simulations and experimental results have proved that the size of the spiral structure is only 30.9% of the conventional EBG structure. Two applications have been shown, including patch antenna with the spiral EBG structure and a double-element microstrip antenna array with low mutual coupling. The measured results show that a gain improvement over 3 dB and a significant reduction of cross polarization in H-plane are obtained. A 6 dB reduction of mutual coupling is achieved in a double-element EBG microstrip antenna array. Index Terms--Cross-polarization, electromagnetic band-gap (EBG), patch antenna, radiation pattern, surface wave.

Leaky coaxial cables can be used as distributed radiators for indoor communications. When the number of slots is large, as it is often the case, the application of a full-wave analysis method is very demanding in terms of both memory and CPU time. In this paper an analysis technique, based on Bloch wave theory is presented. Slots are viewed as discontinuities in an open wave-guide and a suitable basis of orthogonal polynomials is introduced to represent the modal amplitudes pertaining to the continuous spectrum. The radiation properties of the cable are discussed in detail in terms of the excited Bloch waves. Finally, the reflection coefficient at the junction between a uniform and a slotted cable is computed. The results are presented in the form of a chart, for general slot size and spacing. Index Terms--Bloch wave theory, leaky wave antenna.

Reflection and transmission coefficients of plane waves with oblique incidence to a multilayered system of piezomagnetic and/or piezoelectric materials are investigated in this paper The general Christoffel equation is derived from the coupled constitutive and balance equations, which is further employed to solve the elastic displacements and electric and magnetic potentials. Based on these solutions, the reflection and transmission coefficients in the corresponding layered structures are subsequently obtained by virtue of the propagator matrix method. Two layered examples are selected to verify and illustrate our solutions. One is the purely elastic layered system composed of aluminum and organic glass materials. The other layered system is composed of the novel magnetoelectroelastic material and the organic glass. Numerical results are presented to demonstrate the variation of the reflection and transmission coefficients with different incident angles, frequencies, and boundary conditions, which could be useful to nondestructive evaluation of this novel material structure based on wave propagations. Keywords: reflection and transmission coefficients, magnetoelectroelastic material, layered structure, wave propagation

An improved multilevel Green's function interpolation method (MLGFIM) with adaptive phase compensation (APC) is proposed. The difficulty in applying interpolation approaches to the fast varying phase term in the integral equation kernel for full-wave electromagnetic (EM) simulations is eradicated by using the phase compensation and adaptive direction separation (ADS). The multilevel tree structure in MLGFIM keeps the number of direction separation invariant at all levels, attributing to the recursive interpolation with multilevel phase compensation. The proposed MLGFIM-APC in conjunction with the Lagrange-Chebyshev interpolation yield an O(N log N) CPU time and O(N) computer memory requirement for surface scattering problems. By introducing a transition level, the MLGFIM-APC can adaptively incorporate interpolation techniques of conventional interpolation (CI), transition interpolation (TI) and phase-compensation interpolation (PI), corresponding to electromagnetic simulation of problems of small, moderate, and large electrical sizes, respectively. Large-scale microstrip antenna arrays are simulated to illustrate the accuracy and efficiency of the proposed method. It is found that the CPU time scales better than O(N log N) for these co-planar problems. Index Terms--Adaptive direction separation, adaptive transition, Lagrange-Chebyshev interpolation, multilevel Green's function interpolation method with adaptive phase compensation (MLGFIM-APC), phase compensation (PC).

We study TM and TE diffraction by a perfectly conducting half-plane in presence of a perfectly conducting flat strip of finite width and infinite length; the edges of the strip are parallel to the edge of the half-plane. The relevant integral equations with unknowns the induced current densities on the strip are solved by a Nystrom and a Galerkin method that fully account for the singular nature of the kernels and the singularities of the solution at the edges. The proposed algorithms are highly accurate, and appear to converge exponentially as shown by detailed numerical examples and case studies. The Nystrom method is the most efficient of the two methods because of its simple formulation, fast computer implementation, and much less effort in computing the matrix elements. When the strip is coplanar to the half-plane, an additional formulation method in terms of equivalent surface magnetic currents is possible in the framework of the field equivalence principles. This alternative method is applied in order to validate the algorithms and test their accuracy. Index Terms--Electromagnetic diffraction, Galerkin method, integral equations, Nystrom method, strip scatterers.

Radiation features are studied for a grounded wire-medium slab excited by a simple canonical source, i.e., a horizontal electric dipole. For the first time, an approximate analysis based on a homogenized model for the wire medium as well as a rigorous full-wave analysis of the actual periodic structure are presented. The homogeneous model takes into account both anisotropy and spatial dispersion of the metamaterial medium in the long-wavelength regime. One rather surprising result is that this structure allows for directive pencil beams at broadside that are azimuthally symmetric (in spite of the directionality of the wires). The structure also allows for conical beams that point at a chosen scan angle, where the beam angle and beamwidth are azimuthally independent, and the beam peak in the elevation planes remains approximately constant during the scanning process, in contrast with other types of planar leaky-wave antennas. These remarkable features are explained in terms of the azimuthal independence of the wavenumber for the leaky mode that is responsible for the beam. Index Terms--Artificial dielectrics, directive antennas, leaky waves, metamaterials, wire medium.

The performance of multibeam focal plane arrays feeding a single aperture is usually reduced due to conflicting requirements on the feed elements. Dense packing is usually required to minimize the beam separation, while typically large feed apertures are needed to provide the high feed directivity to reduce spillover losses from the reflector. In this paper the use of dielectric super-layers to shape the radiation pattern of each feed is demonstrated. The shaping is obtained by exciting, according to design, a pair of TE/TM leaky waves. The spillover from the reflector is reduced without physically increasing the dimensions of each single element aperture. A prototype of a feed array composed of 19 waveguides arranged in a hexagonal lattice was designed, manufactured and tested. The measured embedded patterns provided an increase of the edge of coverage gain, with respect to the free space case, of at least 0.6 dB in an operating bandwidth (BW) of [approximately equal to] 12%. Moreover when reactive loading of adjacent feeds is adopted the increase in the edge of coverage with respect to the free space case was demonstrated to be larger than 1.6 dB over a 3% BW. Index Terms--Leaky wave antennas, leaky waves, reflector antenna feeds, reflector antennas.

This paper presents an approach and associated circuitry for harvesting near maximum output power from electromagnetic waves in the RF/microwave region of the spectrum with variable incident power densities in the range of tens of [micro]W/[cm.sup.2]. It is shown that open loop resistor emulation at the input port of a power converter is a suitable solution for tracking the peak power point of a low-power rectifying antenna source over a wide range of incident RF power densities. A boost converter with a simple low-power control approach for resistor emulation is presented. A hardware design example with detailed efficiency analysis is given using commercially available discrete circuitry. Experimental results are presented for a system harvesting 420 [micro]W to 8 [micro]W from a 6 cm x 6 cm rectifying antenna with incident RF power ranging from 70 [micro]W/[cm.sup.2] to 30 [micro]W/[cm.sup.2], respectively. The results demonstrate that resistor emulation is a simple and practical approach to energy harvesting with variable low-power radiative RF sources. Index Terms--DC-DC, low power, maximum power point tracking, resistor emulation, RF energy harvesting.

We investigate the possibility of using the modal theory of the electromagnetic propagation in rectangular or circular tunnels, to satisfactorily interpret experimental results, including polarization, in arched tunnels. This study is based on extensive measurement campaigns carried out in the 450 MHz-5 GHz frequency range. Index Terms--Modal theory, polarization, propagation, tunnel.

A new set of higher order hierarchical basis functions based on curvilinear triangular patch is proposed for expansion of the current in electrical field integral equations solved by method of moments. The hierarchical two-level spectral preconditioning technique is developed for the generalized minimal residual iterative method, in which the multilevel fast multipole method is used to accelerate matrix-vector product. The sparse approximate inverse (SAI) preconditioner based on the higher order hierarchical basis functions is used to damp the high frequencies of the error and the low frequencies is eliminated by a spectral preconditioner in a two-level manner defined on the lower order basis functions. The spectral preconditioner is combined with SAI preeonditioner to obtain a hierarchical two-level spectral preconditioner. Numerical experiments indicate that the new preconditioner can significantly reduce both the iteration number and computational time. Index Terms--Eleetromaguetic scattering, generalized minimal residual (GMRES) algorithm, multilevel fast mnitipole method (MLFMM), preconditioning techniques, sparse approximate inverse (SAD.

The diffusion behavior of electromagnetic (EM) waves in two dimensional (2-D) multipath media is studied through integral equation based full wave Monte Carlo simulations. The influences of some physical factors are explored, among which the area density of the embedded obstacles manifests itself to be the most important one in determining wave diffusion. A lossy system starts to behave diffusively when the area density approximately exceeds 5%, and the diffusion equations are generally applicable for predicting power decay. At low densities, the power-distance relation of the waves appears to follow power laws. The sizes and shapes of the obstacles have a secondary effect on the diffusion of waves. Whenever a system contains small objects or objects with reflecting sides, the waves therein are more diffusive and the diffusion equation approximates the reality more accurately. Absorption loss decreases wave diffusion in general, but our results show that the diffusion equation for a system with very lossy but small obstacles can work very well for predicting power decay. Index Terms--Diffusion, Monte Carlo simulation, multiple scattering, random media, transport theory.

This paper presents the fundamentals of the so-called 'Equivalent Cable Bundle Method' for the calculation over a large frequency range of common-mode currents induced on cable bundles by an electromagnetic (EM) perturbation. In particular, the method aims at overcoming the limitation of the multiconductor transmission line theory (MTLN), which is based on the propagation of the quasi-transverse EM (TEM) mode and efficiently used only at 'low frequencies.' The purpose of the method described here is to reduce the computation time by reducing the complexity of the cable bundle models. After a short presentation of the 'high frequency' coupling problem, first, the theoretical basis of the method, and, second, the numerical and experimental validations performed on prototypal cable bundles, in order to illustrate the efficiency and the advantages of the method, are presented. The method described in this paper is considered as a required first step in order to prepare wider applications on real systems in the near future. Index Terms--Cable bundle, cable harness, electromagnetic topology, numerical modeling.

The shielding performance of a planar metamaterial wire-medium (WM) screen under plane-wave illumination is studied. The screen consists of a finite number of periodic layers of thin conducting cylinders embedded in a dielectric matrix; in the low-frequency limit and for waves with the electric field polarized along the wire direction, such a screen can be modeled as a homogeneous slab with a plasma-like dispersive permittivity. In particular, well below the plasma frequency, the effective relative permittivity is negative and very large in absolute value, giving rise to high values of the shielding effectiveness. A comparison with a conventional planar metal screen is reported, showing how the proposed structure can be designed to be advantageous in terms of low density and weight saving. In order to be effective against arbitrarily polarized waves, the original structure is modified, adding a second WM screen with wires orthogonally oriented with respect to the first one. Numerical results are provided that illustrate the validity of the homogenized model in predicting field levels both near to and far from the screen and show the shielding performance attainable with the proposed metamaterial screen in both single- and double-layer configurations at normal incidence. Index Terms--Artificial materials, electromagnetic screen, metamaterials, shielding effectiveness (SE), wire medium (WM).