Abstract-This article discusses the gain-frequency characteristics of most competing modes of azimuthally periodic vane-loaded cylindrical waveguide interaction structure for gyrotron traveling wave tube (gyro- TWT) amplifier, which is the device of increasing importance because of its high-power and broad bandwidth capabilities. Vane-loading is identified as a means to achieve a low-beam energy, high-harmonic, low-magnetic field, mode-selective and stable operation of a gyro- TWT, and thus the development of a simple approach to the analysis of a vane-loaded gyro-TWT have been identified as a problem of practical relevance.

The approximate analytical solution of the integral equation concerning the equivalent magnetic current in the narrow slot, coupling two electrodynamic volumes, has been obtained by the averaging method. The formulas and the plots for currents and the coupling coefficients of longitudinal and transverse slots in the common walls of rectangular waveguides are represented. By means of the induced magnetomotive forces method using basis functions of current distribution, obtained by the averaging method, the following electrodynamic structures have been considered: the electrically long longitudinal slot in the common broad wall of rectangular waveguides; two symmetrical transverse slots in the common broad wall of rectangular waveguides; the transverse slots system in the common broad wall of rectangular waveguides. The problem about the resonant iris with the arbitrary oriented slot in the plane of cross-section of a rectangular waveguide has been solved by the averaging method. The problem about stepped junction of two semi-infinite rectangular waveguides with the impedance slotted iris has been solved by the induced magnetomotive forces method. The analytical formulas for the distributed surface impedance of homogeneous and inhomogeneous magnetodielectric coatings of iris surface have been obtained. For a greater number of the considered electrodynamic structures the calculated values are compared with the results, obtained by numerical methods (also using commercial programs) and the experimental data.

We investigate the structural parameters for the formation of omnidirectional photonic band gap in one dimensional photonic crystal. Simple transfer matrix method is used for calculations. The effect of two parameters, namely, refractive index contrast and filling fraction on omnidirectional reflection is investigated. We find from our study that when n_L, n_i, n_s and d are fixed, omnidirectional bandgap increases with increasing nH/nL i.e., with increasing nH. Therefore, omnidirectional bandgap can be increased by using the material of high refractive index nH when the low index material nL is fixed. We also find that for the considered system of Si-SiO₂, omnidirectional reflection range increases with filling fraction, goes to a maximum value and finally comes to zero. The maximum value of the omnidirectional reflection range is obtained at a value of 0.29 of the filling fraction. The range for allowable values of refractive index of ambient medium n_i has also been estimated.

This paper investigates the characteristics of electromagnetic wave propagation in biaxially anisotropic left-handed materials (BA-LHMs) theoretically and numerically. We discuss under what conditions the anomalous refraction or reflection will occur at the interface when a plane wave passes from one isotropic right-handed material into another BA-LHM. Meanwhile the refraction angle of the wave vector and that of the Poynting power are presented when the anomalous refraction takes place. According to the theoretical analysis,sev eral sets of constitutive parameters of BA-LHMs are considered. Then the anomalous refraction or reflection of the continuous-wave (CW) Gaussian Beam passing from free space into BA-LHMs are simulated by the finite difference time domain (FDTD) method based on the Drude dispersive models. The simulated results are in agreement with theoretical results,which validates the theoretical analysis.

An efficient method based on bees algorithm (BA) for the pattern synthesis of linear antenna arrays with the prescribed nulls is presented. Nulling of the pattern is achieved by controlling only the amplitude of each array element. Numerical examples of Chebyshev pattern with the single, multiple and broad nulls imposed at the directions of interference are given to show the accuracy and flexibility of the BA.

Asup erstrate layer is used to enhance the directivity of the small radiation sources such as Microstrip Patch Antennas. In this paper, we use square loop frequency selective surface (SLFSS) configuration to design the superstrate layer. To compact the structure, we propose a new single layer square loop FSS configuration that operates in two frequency bands such as multi-layer SL-FSS. Simulation results are shown to have good agreement with experimental results.

Electromagnetic Interference (EMI) is becoming a crucial issue in the era of modern electronic systems. For EMI measurement, it is required to place a sensor to receive the radiation from the equipment in a suitable test environment. The performance of the sensor depends on its Antenna Factor, which is the ratio of the incident electric field on the antenna surface to the received voltage at the load end across 50Ω resistance. FDTD is one of the efficient numerical techniques to solve radiation and scattering problem in any environments. To the best of the knowledge of the authors no literature is available where FDTD is used to evaluate the Antenna Factor. Here, in this work we applied FDTD to predict the performance of dipole antenna when it is used as a EMI sensor. The results presented here for free space environment are compared with published results.

The scattering behaviour of fractal based metallodielectric structures loaded over metallic targets of different shapes such as flat plate, cylinder and dihedral corner reflector are investigated for both TE and TM polarizations of the incident wave. Out of the various fractal structures studied,square Sierpinski carpet structure is found to give backscattering reduction for an appreciable range of frequencies. The frequency of minimum backscattering depends on the geometry of the structure as well as on the thickness of the substrate. This structure when loaded over a dihedral corner reflector is showing an enhancement in RCS for corner angles other than 90^â—¦.

An effective numerical solution is presented for the plane wave scattering by multilayered periodic arrays of dielectric spheres. The treated structure is a fundamental model of photonic crystals having three-dimensional periodicity. The problem is analyzed by the mode matching method, where the electromagnetic fields in the air and dielectric regions are approximated by using the Floquet harmonics and vector spherical wave functions, respectively. They are matched on the junction surfaces in the least squares sense. Introduction of sequential accumulation in the process of QR decomposition reduces the computation time from O(Q³) to O(Q¹) and the memory requirement from O(Q²) to O(Q¹), with Q being a number of sphere layers. Numerical results are given for CPU time, speed of convergence, and some band gap characteristics.

There are some limitations on the statement of classic Helmholtz theorem although it has abroad application. Actually, it only applies to simply connected domain with single boundary surface and does not provide any conclusion about the domain where discontinuities of field function exist. However, discontinuity is often encountered in practice, for example, the location of surface sources or interface of two kinds of medium. Meanwhile, most existing versions of Helmholtz theorem are imprecise and imperfect to some extent. This paper not only tries to present a precise statement and rigorous proof on classic Helmholtz theorem with the accuracy of mathematical language and logical strictness, but also generalizes it to the case of multiply connected domain and obtains a generalized Helmholtz theorem in the sense of Lebesgue measure and Lebesgue integral defined on three-dimensional Euclidean space. Meanwhile, our proof and reasoning are more sufficient and perfect. As an important application of the generalized Helmholtz theorem, the concepts of irrotational and solenoidal vector function are emphasized. The generalized Helmholtz theorem and the present conclusion should have important reference value in disciplines including vector analysis such as electromagnetics.

A new algorithm for numerical evaluation of the fields in the near zone of conducting scatterers or antennas of arbitrary shape is developed in the present work. This algorithm is simple, fast, robust andis basedon a preceding calculation of the current flowing on the conducting surface using the electric filed integral equation (EFIE) technique that employs the Rao-Wilton-Glisson (RWG) basis functions. To examine the validity of the near field computational algorithm developed in the present work, it is applied to calculate the near fieldd ue to plane wave incidence on a variety of conducting scatterers. The solution obtainedfor the fields in the near zone is found to satisfy the boundary conditions on both planar and curved scatterer surfaces and the edge condition for structures possessing edges or corners. The solutions obtainedusing the new algorithm are compared with those obtainedusing some commercial packages that employ the finite-difference-time-domain (FDTD). The algorithm defined in the present work gives results which are more accurate in describing the fields near the edges than the results obtained using the FDTD.

In this paper, an efficient algorithm is presented to analyze the electromagnetic scattering by electrically large-scale dielectric objects. The algorithm is based on the multi-region and quasiedge buffer (MR-QEB) iterative scheme and the conjugate gradient (CG) method combined with the fast Fourier transform (FFT). This algorithm is done by dividing the computational domain into small sub-regions and then solving the problem in each sub-region with buffer area using the CG-FFT method. Considering the spurious edge effects, local quasi-edge buffer regions are used to suppress these unwanted effects and ensure the stability. With the aid of the CG-FFT method, the proposed algorithm is very efficient, and can solve very largescale problems which cannot be solved using the conventional CG-FFT method in a personal computer. The accuracy and efficiency of the proposed algorithm are verified by comparing numerical results with analytical Mie-series solutions for dielectric spheres.

This paper presents an effective numerical method for the transient analysis of lossy transmission lines. With the discretization of the spatial variation of voltages and currents along the transmission lines while remaining the temporal derivatives unchanged, a semidiscrete model is derived from the telegrapher's equations. The timestep integration method is utilized to derive the recursive scheme of time advancing. A large time step can be used in the computation, meanwhile, its accuracy is guaranteed. Numerical examples are presented to demonstrate the stability and accuracy of the proposed method.

This work presents a fast computational algorithm that can be used as an alternative to the conventional surface-integral evaluation method included in the electric field integral equation (EFIE) technique when applied to a triangular-patch model for conducting surfaces of arbitrary-shape. Instead of evaluating the integrals by transformation to normalized area coordinates, they are evaluated directly in the Cartesien coordinates by dividing each triangular patch to a finite number of small triangles. In this way, a large number of double integrals is replaced by a smaller number of finite summations, which considerably reduces the time required to get the current distribution on the conducting surface without affecting the accuracy of the results. The proposed method is applied to flat and curved surfaces of different categories including open surfaces possessing edges, closed surfaces enclosing cavities and cavity-backed apertures. The accuracy of the proposed computations is realized in all of the above cases when the obtained results are compared with those obtained using the area coordinates method as well as when compared with some published results.

This paper proposes an approximate space-time-frequency field representation for directive Ultra-wideband antennas useful to be introduced into a system-level evaluation tool. Based on the observation that the very near field collected on a plane close to the antenna exhibits a compact support, such a field is processed in the time domain by the two-dimensional Hermite transform. This approach permits to simultaneously express the antenna impulse response and the transfer function by semi-analytical formulas. The theory is demonstrated by numerical examples which highlights that good representations of complex antennas can be achieved by a small set of associate Hermite functions.

When estimating the electric field level in an indoor environment, the usual complexity of the geometry and its large electric size make it necessary to deal with asymptotic assumptions, also known as high frequency techniques. But, even with these assumptions, the computational complexity, and the CPU-time cost, can be very high. Considering this drawback, this paper proposes the implementation of a "Neural Networks System" for fast calculations of the Electric field in 2D-indoor environments.

Pairing an epsilon-negative (ENG) slab with a munegative (MNG) slab can have some unusual features,suc h as zero reflection and complete tunneling without any phase delay,although each of those two slabs has predicable features. In this paper,the conditions of zero reflection are obtained through an exact analysis, not by the equivalent transmission-line (TL) models. The distributions of fields and Poynting vector outside and inside such paired slabs are analyzed,while evanescent waves also are studied. Simulation results validate the salient features of such paired slabs.

In this work, complex propagation constant of substrate integrated waveguide (SIW) with lossy dielectric is determined with the help of the generalized multipole technique (GMT). We then apply the GMT to compute scattering parameters of some discontinuities in SIW. The obtained results are compared with the results generated by a commercial finite-element solver.

A novel low-pass filter using complementary split ring resonators (CSRRs) for transmission zero control and sharp-rejection is presented. Three different CSRRs resonators cells are etched at the ground plane below a low impedance microstrip line for transmission zero control. A demonstration lowpass filter is designed, fabricated and measured. It agreed with the simulated results well.

The extension of an unconditionally stable precise integration time domain method for the numerical solutions of Maxwell's equations to circular cylindrical coordinate system is presented in this paper. In contrast with the conventional cylindrical finite-difference time-domain method, not only can it remove the Courant stability condition constraint, but also make the numerical dispersion independent of the time-step size. Moreover, the first-order absorbing boundary condition can be introduced into the proposed method successfully, whereas the alternating-direction-implicit finitedifference time-domain method may become instable for open region radiation problems terminated with absorbing boundary conditions. Theoretical proof of the unconditional stability is mentioned and the numerical results are presented to demonstrate the effectiveness of the proposed method in solving electromagnetic-field problem.