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.
In the present paper the response of V transmission line to electromagnetic illumination has been obtained. Also in order to determine the VTL frequency operation band for both TE and TM modes a Gaussian pulse source has been applied to the structure. The VTL structure has received considerable attention in high frequency and microwave IC packaging. The purpose of this study is to determine high frequency design considerations in order to reduce the effects of electromagnetic interference (EMI) on the VTL structure and maintain the desired performance. It was observed that the effect of incident EM waves on the V lines performance is considerably lower than conventional microstrips, however the V lines are more sensitive to sources at close proximity. In addition, although the V lines show lower dispersion at higher frequencies, their frequency operation band is limited by a resonance like behavior which is directly related to the V groove dimensions. The full wave analysis is carried out using the Yee-cell based 2 Dimensional Finite Difference Time Domain method (2D-FDTD), while enforcing a very stable and efficient mesh truncation technique.
Space division multiple access (SDMA) is a promising can- didate for improving channel capacity in future wireless communication systems. Considering that discrimination performance of the user in the spatial domain depends on the array arrangement, and as a result the optimum element arrangement for SDMA should be defined, beam- forming play a very important role providing fundamental theory of design procedure. However the pattern of antenna array is determined by array geometry. Two-dimensional (2-D) spatial filters that can be implemented by microstrip technology are capable of filtering the re- ceived signal in the angular domain as well as the frequency domain. This paper focuses on various geometries of eight and nine elements antenna arrays using circularly patch elements as well as hexagonal ar- ray with seven elements. The network throughput is further analyzed to determine if using a fully adaptive pattern (LMS algorithm gener- ated pattern) results in a higher throughput with or without presence of mutual coupling effects.
A rigorous semi-analytical solution is presented for electromagnetic scattering from an array of circular cylinders due to an obliquely incident plane wave. The cylinders are illuminated by either TMz or TEz incident plane wave. The solution is based on the application of the boundary conditions on the surface of each cylinder in terms of the local coordinate system of each individual cylinder. The principle of equal volume model is used to represent cylindrical cross-sections by an array of circular cylinders for both dielectric and conductor cases in order to proof the validity of the presented technique.
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.
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 âˆ’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
In this paper, a fast method is proposed to calculate wide- band frequency responses of complex radar targets on a personal computer. When frequencies are low, the frequency factor can be separated from space parameters by Chebyshev polynomial approximations of Green's function. Then, matrices from MoM at different frequencies can be rapidly filled, and monostatic RCS can be soon calculated. If frequencies are relatively high, a fast high-order MoM (HO-MoM), in which matrices products are in place of multi- dimension numerical integrations, is presented. That will reduce the CPU time requirement. Lastly, Numerical results are given for various structures and compared with other available data.
Two novel structures for high-Q MEMS tumble capacitors are presented. The proposed designs include full plate as well as the comb structured capacitors. They can be fabricated employing surface micromachining technology which is CMOS-compatible. The structures do not require the cantilever beams which introduce considerable series resistance to the capacitor and decrease the quality factor. Therefore, our proposed structures achieve better Q in a smaller die area. The simulated results for 1 pF full plate capacitor shows a tuning range of 42% and a Q of 47 at 1 GHz. However, with the same initial capacitance, but the comb structure, the tuning range is increased to 43% but the Q is decreased to 45 at 1 GHz. The simulated Pull-in voltage with no residual stress is 3.5 V for both capacitors. The S11 responses are reported for a frequency range from 1 up to 4 GHz.
This paper presents the study of a circular slot antenna for ultrawide-band (UWB) applications. Antenna is fed by a circular open ended microstrip line. The frequency band considered is from 4 to 14 GHz, which has approved as a commercial UWB band. The proposed antenna has a return loss less than 10 dB, phased linear, and gain flatness over the above a frequency band.
Based on the strict and delicate analogue relation between the magnetic moment of rotational charged bodies and the rotation inertia of rigid bodies, a new concept of charge moment tensor I which is different from the existent electric multiple moment is introduced in this paper. And by means of eigenvalue theory of tensor I , the concept of principal axes and principal-axis scalar charge moment are constructed, and further the scalar charge moment of a charged body and the magnetic moment of a rotational charged body around an arbitrary direction are attained. The relationship between the scalar charge moment distributive law of quadric camber and the positive or negative definiteness of tensor I are discussed. Meanwhile Some principles or theorems are extended, generalized, illustrated, and enumerated.
The scattering of electromagnetic plane wave by a perfectly conducting disk is formulated rigorously in a form of the dual integral equations (abbreviated as DIE). The unknowns are the induced surface current (or magnetic field) and the tangential components of the electric field on the disk. The solution for the surface current is expanded in terms of a set of functions which satisfy Maxwell's equation for the magnetic field on the disk and the required edge condition. At this step we have used the method of the Kobayashi potential and the vector Hankel transform. Applying the pro jection solves the rest of a pair of equations. Thus the problem reduces to the matrix equations for the expansion coefficients. The matrix elements are given in terms of the infinite integrals with a single variable and these may be transformed into infinite series that are convenient for numerical computation. The numerical results are obtained for far field patterns, current densities induced on the disk, transmission coefficient through the circular aperture, and radar cross section. The results are compared with those obtained by other methods when they are available, and agreement among them is fairly well.
In this paper we show, theoretically, that total omnidirec- tional reflected frequency band is enlarged considerably by using one- dimensional photonic crystal (PC) structure composed of alternate lay- ers of ordinary material (OM) and left handed material (LHM). From the analysis it is found that the proposed structure has very wide range of omnidirectional total frequency bands for both polarizations in com- parison to the normal PC structure, which consists of alternate layers of ordinary material having positive index of refraction. The proposed structure also has an absolute band gap that can be exploited to trap the light.
This paper presents a simple and alternative approach for the analysis of inductive waveguide microwave components. The technique uses a surface integral equation formulation, in which the contours of the waveguide walls and of the inner obstacles are all discretized using triangular basis functions. In order to avoid the relative convergence problem of other techniques based on mode matching, an alternative port treatment is used. The technique is based on the application of the extinction theorem using the spatial representation of the Green's functions in the terminal waveguides. In addition, the Fast Multipole Method is proposed in order to reduce the computational cost for large problems. Different complex structures are analyzed, including microwave bandpass filters with elliptic transfer functions, waveguide bends and T-junctions. Results show the high accuracy and versatility of the technique derived.
Broken rotor bars and end-ring are common faults in three-phase squirrel-cage induction motors. These faults reduce the developed toque and increase the speed fluctuations of the motor. Meanwhile, developed unsymmetrical magnetic generates noise and vibration in the motor. Local heat around the broken bars may gradually break the adjacent bars and the motor will be finally out of service. Finite element method (FEM) is the most accurate technique for diagnosis and analysis of induction motor, because it can include all actual characteristics of the healthy and faulty induction motors. However, current density is generally considered as input for performance computation process, while fault can inject a large harmonics to the stator current. These harmonics may not be ignored in the fault diagnosis of the motor. In addition, all FE applications consider the steady-state mode of operation. In this paper, a three-phase voltage-fed squirrel-cage induction motor with rotor broken bars is proposed and analyzed for the starting period of the motor. Both no-load and on-load cases are considered. Also, concentrated rotor broken bars under one-pole and the distributed rotor broken bars under different poles are studied and compared.
In this paper, rain statistics of 10 years record in Taiwan area was used to investigate the transmission performance of the Ka- band LMDS system with QAM modulation. Emphasis was placed to investigate the effects of rain fading under M-QAM modulation schemes. It is found that for LMDS cellular network, M-QAM modulation is difficult to provide an effective and reliable high speed transmission for the case of 6 km radius of cell coverage unless the frequency and polarization diversities are applied; otherwise, the cell coverage of service should be shrunk.
This paper presents an approach for the design and optimization of pseudo-gradual transitions in circular waveguides using the genetic algorithm (GA). The characterization of these transitions is carried out by the mode-matching method. This method, associated with the generalized scattering matrix technique, leads to determine the reflection coefficient on the useful band of the studied structures and to observe their frequential behavior. The GA is employed to optimize the choice of geometrical parameters by minimizing a cost function, corresponding to the maximum magnitude of the reflection coefficient in the band. The selection of the most relevant parameters allowed an improvement of the performances for the optimized components. Results of optimization are given for both two and four-section transformers.
The coupled mode approach is applied to the ferrite circular waveguide magnetized through a rotary four-pole transverse bias magnetic fields. The plausible mathematical model of the ferrite waves propagation in the guide is developed which includes gyromagnetic interaction of two orthogonal TE11 isotropic modes. The importance of the birefringence effect in determining of phase shift and polarization phenomena are thereby demonstrated. As a result basic design consideration of the circular polarizer applied as a "half-wave plate" in rotary-field phase shifter are provided.