Aclosed-form formula, the discrepancy parameter, which has been defined as the ratio of the modal expansion coefficients between the electromagnetic field obtained from the image approximation and the incident electromagnetic field, has been proposed for the evaluation of the validity of the image approximation in the electromagnetic wave propagation, i.e., Love's equivalence principle, and the electromagnetic wave scattering, i.e., the induction equivalent and the physical equivalent, in the cylindrical geometry. The discrepancy parameter is derived through two equivalent methods, i.e., the vector potential method through the cylindrical addition theorem and the dyadic Green's function method, for both the TE and TM cylindrical harmonics. The discrepancy parameter justifies the fact that the image approximation approaches the exact solution for the cylindrical surface of infinite radius. For the narrow-band field with limited spectral component in k space, the cylindrical modal expansion of the electromagnetic wave into the TE and TM cylindrical harmonics can be separated into the forward-propagating wave that propagates forward and the back-scattered wave that is back-scattered by the PEC surface, within the image approximation. The discrepancy parameter shows that the validity of the image approximation depends on the property of the incident field and the radius of the cylindrical surface, i.e., the narrow-band field and the surface of a large radius are in favor of the image approximation, which has also been confirmed by the numerical result.

In this paper, the higher order hierarchical basis functions are employed to solve the electric field integral equation for computing electromagnetic scattering from three-dimension bodies comprising both conducting and dielectric objects. In higher-order methods of moments (HO-MoM), the equivalent surface electric and magnetic currents are usually expanded by the same basis functions, which are not appropriate in our problem here. The pointwise orthogonal basis functions respectively for electric and magnetic currents are proposed in our improved HO-MoM. Quadrilateral patches are used in curvilinear geometry modeling since they result in the lowest number of unknowns. Numerical solution procedure is particularly analyzed, and numerical results are given for various structures and compared with other available data lastly.

In this paper we investigate the effect of replacing the ordinary rectangular microstripp atches in a linear antenna array with fractal patch elements. It is shown that using fractal patches substantially decreases the Mutual Coupling between elements. The effects of fractal type, spacing between elements, feed point location and number of parasitic elements on array performance has been studied.

In this paper, we present a comparison study between phase-only and amplitude-phase synthesis of symmetrical dual-pattern linear antenna arrays using floating-point or real-valued genetic algorithms (GA). Examples include a sum pattern and a sector beam pattern. In the former, phase is only optimized with predetermined Gaussian amplitude distribution of fixed dynamic range ratio (|^amax / ^amin|) and in the latter, both are optimized with less dynamic range ratio than the former and yet share a common amplitude distribution.

This paper presents an icosahedron-based spherical antenna array for phase mode processing. In this topology, the interelement spacing is almost identical. This feature is useful for threedimensional beam scanning and for reducing the effects of mutual coupling. The use of directional elements in this array for wideband synthesis is discussed, and our results show that the use of such elements can overcome the limitations of rapid variations in the amplitude of the far-field mode over a wide frequency band and enable such array to synthesize wideband patterns.

A novel method is introduced to synthesize microstrip Nonuniform Transmission Lines (NTLs) for matching between two arbitrary complex frequency dependent impedances in a wideband or multi-band frequency range. First, stripwidth or the characteristic impedance function of the microstrip NTL is expanded in a truncated Fourier series. Then, the optimum values of the coefficients of the series are obtained through an optimization approach. The usefulness of the proposed method is verified using some examples.

In this paper, new circuit models are used to calculate the induced fields in biological media exposed to an incident plane wave in the two-dimensional cases. These models represent the induced fields in the medium using the lossy long transmission line model [1]. The voltages and currents in the circuit model simulate the electric and magnetic fields in the medium. The response of the medium to the incident wave is represented by equivalent conduction and polarization current sources in the medium. These currents are used as the excitation sources in the circuit model from which the required induced fields are obtained. An accurate absorbing impedance boundary condition for open boundaries is used which considerably reduces the matrix dimensions. The validity of these models is tested in the problem of absorption of E- and H-waves by biological multilayered cylinders. Results are compared with available analytical and numerical solutions.

The far-field radiation characteristics of an infinitesimal dipole embedded between two partially reflective surfaces (PRS) to obtain high directivity are studied analytically. The analysis is based on integral summation of spectral radiation fields of the source in cylindrical coordinate, so that we can find the effects of transmission and reflection coefficients of PRS on all components of primary radiation source. The analysis shows that due to the existence of TE_z and TM_z modes for horizontal dipole source, the effects of PRSs are different for each mode. Also, this study shows that by adjusting the spacing of the plates, it is possible to achieve high directive multibeam patterns.

In this paper a Polarized Optical Orthogonal Code (Polarized-OOC) is proposed by exploiting the polarization property of the fiber and the chip's polarization state. The polarized-OOC code is generated using the concept of Mark Position Difference (MPD) set. Polarized-OOC code cardinality is shown to be two times that of the conventional OOC which reflects an increase in the number of supported users. Furthermore, since the correlation properties of the constructed code are the same as that of conventional OOC, error rate performance is evaluated in the same way as in conventional OOC. Also, a simple procedure for fiber-induced polarization rotation compensation is introduced. We then use simulations to show that relative polarization axis misalignment between the desired user and interfering users leads to violation of the correlation properties of the proposed code.

The properties of a grounded dielectric slab with double negative (DNG) metamaterials are investigated in this paper. Dramatically different dispersion curves of evanescent surface modes (electromagnetic fields exponentially decay both in air and inside the slab) are observed. They are highly dependent on the medium parameters. As the counterpart of the improper complex leaky modes in a double positive (DPS) medium, the complex modes in a DNG medium are proved to be exclusively proper. They have exponentially decaying fields in the air region and are termed complex surface modes. It is found that there are an infinite number of complex surface modes and they cannot be suppressed. The Poynting vectors of complex surface modes are studied and it is proved that their integrals along the transverse direction are simply zero. The complete mode spectrum of the dielectric slab for both DPS and DNG media are tabled and compared. Surface wave suppression is discussed and its necessary and sufficient conditions are presented.

Based on a generalized Helmholtz's identity, definitions of an irrotational vector and a solenoidal vector are reviewed, and new definitions are presented. It is pointed out that the well-known uniqueness theorem of a vector function is incomplete. Although the divergence and curl are specified, for problems with finite boundary surfaces, normal components are not sufficient for uniquely determininga vector function. A complete uniqueness theorem and its two corollaries are then presented. It is proven that a vector function can be uniquely determined by specifyingits divergence and curl in the problem region, its value (both normal and tangential components) on the boundary.

In this paper, a conceptual schematic for calibration of large phased array antenna is presented. Derived from an earlier work by the authors, the presentation demonstrates a simple yet innovative schematic of inserting time delay units with each element in the array which can be used to generate both SUM and DIFFERENCE pattern. Both these patterns are electronically steerable. The calibration is done using SUM-DIFFERENCE pattern. PIN switches are used to insert proper time delay units. Thus the schematic is completely programmable using a microcontroller to control the insertion of time delay. The details of the schematic is presented along with the generated antenna patterns.

Geometry of grating structure has been analyzed to maximize electromagnetic energy deposition onto the active region of a silicon photodetector. The concept of Brewster angle to minimize reflection from the grating surface and a differences-in-time technique to focus incoming electromagnetic radiation on the substrate has been applied to optimize the grated structure that amplifies transmitted energy through grating-substrate interface. The computed electric field at the interface for the new grating geometry has been found to be approximately 1.5 times higher than that of a square-shape gratings reported earlier. Also the average power depositions and electric field distributions on the grating-substrate interfaces have been studied which revealed the superiority of the proposed optimum structure.

When the finite-difference time-domain method is used to compute waveguide structures, incident waves are needed for calculating electrical parameters (e.g., the scattering parameters), and effective absorbing boundary conditions are required for terminating open waveguide structures. The incident waves are conventionally obtained with inefficient three-dimensional (3D) simulations of long uniform structures, while the absorbing boundary conditions reported so far do not perform well at or below cut-off frequencies. To address the problems, we propose a novel one-dimensional (1D) finite- difference time-domain method in this paper. Unlike the other methods developed so far, the proposed method is derived from the finite-difference time-domain formulation, and therefore has the same numerical characteristics as that of the finite-difference time-domain method. As a result, when used to obtain an incident wave, it produces results almost identical to those produced by the conventional finite- difference time-domain method except computer rounding-off errors. When used as the absorbing boundary condition, it produces reflections of less than −200 dB in entire frequency spectrum including the cut-off frequencies.

Horizontal roll vortex pairs are dynamical structures that transfer energy and emissions from wildfires into the atmosphere. The vortices form at the edges of an intense line wildfire and emulate two cylinders, which form two curvatures of a biconcave thermal lens. Wildfire plume provides a dielectric material for the dielectric lens, whose permittivity is influenced by the nature, quantity of constituents (e.g., potassium and graphitic carbon) and variation of temperature with height in the plume. The environment created by the plume is radio sub-refractive with an effect of spreading radio wave beams. A numerical experiment was carried out to quantify loss of Ultra High Frequency (UHF) radio signal intensity when high intensity wildfire- induced horizontal roll vortices intercept UHF propagation path. In the numerical experiment, a collimated radio wave beam was caused to propagate along fuel-fire interface of a very high intensity wildfire in which up to two roll vortex pairs are formed. Maximum temperature of the simulated wildfire was 1200 K. Flame potassium content was varied from 0.5-3.0%. At 3.0% potassium content, a vortex pair imposed a maximum radio ray divergence of 2.1 arcmins while two vortex

This paper presents a planar microstrip-fed tab monopole antenna for ultra wideband wireless communications applications. The impedance bandwidth of the antenna is improved by adding slit in one side of the monopole,in troducing a tapered transition between the monopole and the feed line,and adding two-step staircase notch in the ground plane. Numerical analysis for the antenna dimensional parameters using Ansoft HFSS is performed and presented. The proposed antenna has a small size of 16 x 19mm,and provides an ultra wide bandwidth from 2.8 to 28 GHz with low VSWR level and good radiation characteristics to satisfy the requirements of the current and future wireless communications systems.

In this phase of the attempt to advance finite dimensional algebraic function approximation technique in eigenvalue problems of lossless metallic guides filled with anisotropic and/or inhomogeneous media,to exact analysis in infinite dimensions,it is seen that the problem in infinite dimensions,can be reduced to finite dimensions,b y virtue of a result in perturbation theory. Furthermore,it is found that analysis results of algebraic function approximation,can be adapted to infinite dimensions too,at worst by introduction of some additional arguments.

Theoretical results on the effect of antenna mutual coupling (MC) on capacity of multiple-input multiple-output (MIMO) wireless channels are presented in this paper with particular emphasis on the case of high signal to noise ratio (SNR) scenario. Two cases are considered, 1- channel capacity variations due to MC effect on correlation properties and target average receive SNR and 2- channel capacity variations due to MC effect on correlation properties at fixed average receive SNR. It is shown that the effect of MC on MIMO channel capacity can be positive or negative depending on the propagation environment spatial correlation properties and the characteristics of the transmitter and receiver MC matrices. Conditions where MC has positive and negative effects on MIMO channel capacity in the two considered cases are identified. Numerical results for half wavelength dipole antenna supporting the theoretical observations are presented.

A general method is proposed to analyze periodic or aperiodic Coupled Nonuniform Transmission Lines (CNTLs). In this method, the per-unit-length matrices are expanded in the Fourier series. Then, the eigenvalues of periodic CNTLs and so the S parameters of aperiodic CNTLs are obtained. The validity of the method is studied using a comprehensive example.

The rigorous modeling and analysis of electromagnetic wave transformation and radiation from the periodic boundary of metamaterial are presented. The nature of the phenomenon of resonant radiation and the influence of various parameters on it are investigated. The study is carried out with the objective of potential applications to antenna design. Simulated results show that very high directivity can be obtained and that beam steering can be achieved by adjusting proper parameters.