To efficiently solve large dense complex linear system arising from electric field integral equations (EFIE) formulation of electromagnetic scattering problems, the multilevel fast multipole method (MLFMM) is used to accelerate the matrix-vector product operations. The inner-outer flexible generalized minimum residual method (FGMRES) is combined with the symmetric successive overrelaxation (SSOR) preconditioner based on the near-part matrix of the EFIE in the inner iteration of FGMRES to speed up the convergence rate of iterative methods. Numerical experiments with a few electromagnetic scattering problems for open structures are given to demonstrate the efficiency of the proposed method.
The shadowing relationship between facet elements can be determined rapidly through analytical expressions. On the basis of modeling using curved surfaces, an effective shadowing processing algorithm is proposed which is in combination with that used in the shadowing judgement of facet elements. Firstly several sampling points are taken on the ergodic curved surface element to construct a group of facet elements, which can replace the curved surface element. Then the shadowing processing between the stationary phase point and the ergodic curved surface element is converted to that between the stationary phase point and several facet elements, thus avoiding utilizing optimization method and can increase the computation speed. Similarly, the shadowing processing between the stationary phase segment and the ergodic curved surface element is converted to that between the stationary phase segment and several facet elements. And the trimming algorithm is used to accurately find the visible part of the stationary phase segment, which gets rid of the rough shadowing processing technique that determines the visibility of the whole stationary phase segment through the visibility of the center of the stationary phase segment. Therefore, the computation precision is greatly improved. When there exists a huge number of curved surfaces, maximum-minimum preprocessing is utilized to increase the computation speed. Examples show that this novel algorithm is superior to the traditional one in both computation speed and precision.
Based on composite right/left-handed (CRLH) transmission line (TL),a novel series feed network for microstrip arrays is proposed and its theoretical analysis and experimental results are presented. In the present structure,p ower dividers and open-ended stubs are employed to even the amplitude distributions among different output ports,while CRLH TLs and short meandering lines are used to compensate the phase delay caused by the different lengths of righthanded (RH) TLs. Finally,an X-band series feed network is designed and fabricated as an example. The simulated and measured results indicate that the present design can achieve even amplitude and phase distributions among different output ports in the range of 8.8-9.6 GHz. And it has other advantages such as a compact size of 350mm×50mm and good return loss which is higher than 22 dB in the operation frequency.
The solution to the problem of far field radiation from an arbitrarily oriented Hertzian dipole in an electrically gyrotropic medium is found with the application of dyadic Green's function (DGF) technique. The form of the DGF, which is expressed as the sum of two single dyads, simplifies the derivation of the far fields significantly in comparison to the existing methods. The far field integral is evaluated analytically using the method of steepest descent. The numerical results for the radiation fields are presented in different frequency bandwidth using Clemmow-Mually-Allis (CMA) diagram. It is shown that the operational frequency bandwidth and the orientation of the antenna, which give the highest directivity and gain, can be determined when the CMA diagram is employed. Our analytical results are compared with the existing ones which were obtained using different techniques. Agreement is observed on all of them. The results presented in this paper can be used for radiation problems involving space exploration, radio astronomy or laboratory plasmas.
Electromagnetic scattering problems involving inhomogeneous objects can be numerically solved by applying a method of moment's discretization to the hypersingular volume integral equation in which a grad-div operator acts on a vector potential. The vector potential is a spatial convolution of the free space Green's function and the contrast source over the domain of interest. For electrically large problems, the direct solution of the resulting linear system is expensive, both computationally and in memory use. Conventionally, the fast Fourier transform method (FFT) combined Krylov subspace iterative approaches are adopted. However, the uniform discretization required by FFT is not ideal for those problems involving inhomogeneous scatterers and sharp discontinuities. In this paper, a nonuniform FFT method combined weak form integral equation technique is presented. The method performs better in terms of speed and memory use than FFT on the configuration involving both the electrically large and fine structures. This is illustrated by a representative numerical test case.
In this paper, Maslov's method has been used to obtain the high frequency field refracted by a hyperboloidal focusing lens. High frequency problem which contains caustic region is transformed into caustic free problem by transforming the situation into mixed domain. The high-frequency solution that includes the caustic region is obtained from geometrical optics. The defect in high frequency solution due to geometrical optics is overcomed by Maslov's method. Numerical computations are made for the field pattern around the caustic. The results are found in good agreement withobtained using Debye-Wolf focusing integral.
We study the influence of the resistivity frequency dispersion effects on the magnetotelluric (MT) response. Impedivity is the term used to indicate the frequency dependent resistivity in rocks. The impedivity functions, used in this paper, have been derived from the general solution of the motion equation of a charge carrier, discussed in a previous paper. A 1D three-layered earth section, with the second layer assumed to be dispersive, is considered to analyze the distortions due to dispersion on the modulus and phase of the MT responses on the earth's free surface. The MT responses of the section, where the dispersive layer is attributed an impedivity function describing at first a positive, then a negative and finally a resonant dispersion model, are computed for various combines of the dispersion parameters. A general conclusion is that the dispersion effects can strongly influence the MT response either in recognizable or in subtle forms. In the former case, the distortions appear as either steeply rising and/or descending curve branches or spike-like deltas, not compatible with a dispersion-free section. In the latter case, instead, the MT curves preserve the typical behavior for a dispersion-free section, and may thus erroneously be modeled by a section, where the dispersive layer is totally suppressed. In both case, disregarding the distortion effects may lead to misleading conclusions as to the physical properties of the surveyed structures.
Plane-wave reflection from and transmission through a slab of uniaxial anisotropic medium is studied and the concept of ZAP (Zero-Axial-Parameter) medium sheet is defined as the limiting case when the axial parameters and the thickness of the slab vanish simultaneously. It is shown that the ZAP sheet may act as a spatial filter for the incident waves with transmission in a narrow cone around normal direction. Such a sheet may find application in narrowing the radiation beam and reducing sidelobes of an antenna or as a computer privacy filter in optical frequencies.
The case where the background material of a cloak possesses magnetoelectric coupling is investigated in this paper, for examples, the base medium is bianisotropic or an isotropic medium moving with uniform speed which may be comparable with that of light. The specifically proposed constitutive parameters for such kind of cloak show more complicated bianisotropic property, which can not be simply produced by an isotropic medium in a uniform-velocity motion.
The broadband wavelength conversion based on four-wave mixing in a silicon nanowire waveguide is theoretically investigated by taking into account the influence of the waveguide loss and free-carrier absorption on the phase-matched condition. The lossy wavelength conversion is compared with the lossless one in terms of conversion efficiency and bandwidth. The size of the silicon-oninsulator nanowire waveguide is optimized to be 400nm × 269nm for broadband wavelength conversion by realizing a flattened dispersion. The pump wavelength is also optimized to 1538.7nm in order to further enhance the conversion bandwidth. A 3-dB conversion bandwidth of over 280nm is achieved in the optimized waveguide with the optimized pump wavelength.
The modal dispersion relation of electromagnetic waves in a Bragg fiber having plasma in the cladding regions is investigated analytically. The proposed Bragg fiber consists of a low index central region having air surrounded by a large number of periodic cladding layers of alternating high and low refractive indices of dielectric and plasma respectively. The modal dispersion relation is obtained by solving Maxwell wave equations using a simple boundary matching method. The analysis shows that the normalized frequency parameter (also called V -number) is frequency independent. This indicates that the proposed Bragg fiber may be used for single mode operation without high frequency limitation as well as with little loss of energy compared to the conventional dielectric waveguide.
Based on message passing interface (MPI) of the PC Clusters, the parallel method of moment (MOM) is applied to the electromagnetic (EM) scattering from one dimensional (1-D) large scale PEC Gaussian rough surface with two dimensional (2-D) PEC cylinder above it with low grazing incidence. The conjugate gradient method (CGM) for solving MOM matrix equation is parallelized according to the property of MPI in this work. The parallel computational efficiency and validity are shown by several numerical simulations, in which it is proved that the proposed method supplies a novel technique for solving the problem of the composite EM scattering for a 2-D target above 1-D large scale rough surface. Finally, the influences of root mean square (rms) height, the correlation length of the Gaussian surface, the size and the altitude of the cylinder, the polarization on the bistatic scattering coefficient (BSC) for low grazing incidence are also discussed in detail.
The electromagnetic field distributions in the waveguide of a 915 MHz single-mode microwave sintering applicator equipped with a loading pressure system were simulated using a JMAG-Studio program. The disturbance in the magnetic field as well as in electric field was caused by the insertion of the alumina loading pressure system due to reflection effect of alumina. However, the separated magnetic field and electric field maxima can be obtained by adjusting position of the alumina loading pressure system in the waveguide. The simulation results were evaluated by comparison with experimental measurement.
Based on the improvements of both Genetic Algorithm and Particle Swarm Optimization, a novel IGA-edsPSO (Improved Genetic Algorithm-extremum disturbed simple Particle Swarm Optimization) Hybrid algorithm is proposed in this paper. An improved performance of GA is achieved by reducing the array space. By discarding the particle velocity vector in the PSO evolutionary equation, the sPSO (simple PSO) can avoid the problem of slow later convergence velocity and low precision caused by determining the maximal velocity vector factitiously. And the edsPSO can overstep local extremum point more effectively with the help of the extremum disturbed factor. The proposed IGA-edsPSO Hybrid algorithm is used in the design of the sparse arrays with minimum element spacing constraint. Given the array aperture and the number of the array elements, the suppression of the peak sidelobe level (PSLL) with a certain half power beamwidth (HPBW) restriction is implemented with a high efficiency by optimizing the HPBW and PSLL synchronously. The simulation results show that faster convergence velocity (which means less computation time) and lower sidelobe level are obtained using IGA-edsPSO compared to IGA, standard PSO, GA-PSO and GA-sPSO.
Detailed procedure for Green's function derivation of an annular waveguide is presented in this paper for the first time. The proper components of the electromagnetic fields along with their corresponding Green's functions will be derived in a useful and applicable form. Based on the derived Green's functions, proper set of integral equations are derived in a novel general form which their MoM solution will lead to complete slot field distribution in the annular waveguide slot antenna (AWSA). The proposed theory would be found of high value in circuit modelling and array design of such novel antenna structures in the future.
The rigorous numerical formulation for TE-scattering from a conducting wedge with concaved edge is presented and numerical computations for scattered fields are shown. The radial mode matching technique is used to obtain the scattering field in a series form. The accuracy of the present method is checked with existing solutions of a semi-circular channel and sharp wedge, which are special case of the general geometry of a conducting wedge with concaved edge.
A hybrid method is developed to compute the radiation pattern of antennas on large complex three-dimension carriers. The hybrid method involves computing the radiation fields of the antenna in free space with FEM, characterizing the reflection and diffraction of the carrier to the radiation fields with CRE (Complex Ray Expansion) and UTD (Uniform Theory of Diffraction). The ray technique of SBR using traditional hybrid method is employed by CRE. The shortcomings of the SBR, such as great number of ray trace, distortion and partly shadowing of the rays etc., are overcome by the use of CRE, and the time consuming physical-optics-type integration is replaced by the paraxial approximation of the complex rays. A dipole placed on different carriers are taken as the examples to show the validity of the hybrid method, and the radiation patterns computed by the proposed method are in good agreement with those by FEM. By using the proposed method, the computation of the three dimension radiation pattern of an antenna in a large ship is finished by a PC in 1671.20 seconds.
This paper presents a rhombic patch monopole antenna applied with a technique of fractal geometry. The antenna has multiband operation in that the generator model, which is an initial model to create a fractal rhombic patch monopole, is inserted at each center side of a rhombic patch monopole antenna. Especially, a modified ground plane has been employed to improve input impedance bandwidth and high frequency radiation performance. The proposed antenna is designed and implemented to effectively support personal communication system (PCS 1.85-1.99 GHz), universal mobile telecommunication system (UMTS 1.92-2.17 GHz), wireless local area network (WLAN), which usually operate in the 2.4 GHz (2.4-2.484 GHz) and 5.2/5.8 GHz (5.15-5.35 GHz/5.725-5.825 GHz) bands, mobile worldwide interoperability for microwave access (Mobile WiMAX), and WiMAX, which operate in the 2.3/2.5 GHz (2.305-2.360 GHz/2.5-2.69 GHz) and 5.5 GHz (5.25-5.85 GHz) bands. The radiation patterns of the proposed antennas are still similarly to an omnidirectional radiation pattern. The properties of the antenna such as return losses, radiation patterns and gain are determined via numerical simulation and measurement.
The effects of the surface slopes joint probability density, the shadowing function, the skewness of sea waves and the curvature of the surface on the backscattering from the ocean surface are discussed and an improved two-scale model modified by these four aspects is used to calculate the backscattering coefficient of the dynamic ocean surface. In order to deal with the surface skewness driven by wind, a new complementary term derived from the small perturbation method is included in the improved model, in which the Fourier transform of the third-order cumulant function, surface bispectrum, is employed. On this basis, with the oceanic whitecap coverage taken into account, a composite model for predicting the ocean surface backscattering coefficient is constructed tentatively, which incorporates the volume scattering into the total one. Finally, with the vector radiative transfer (VRT) theory employed, numerical illustrations are carried out for the backscattering coefficients versus wind speed, incidence angle and azimuth angle, respectively. The predictions of the composite model are verified in Ku- and Ka-bands through the comparison of numerical results with many sets of measured data and the aircraft measurement experiment carried out in ZHOUSHAN sea area also supports this model.
This paper links the multipath smart antenna CDMA system signal detection problem to the PARAllel profiles with LINear Dependencies (PARALIND), and derives a deterministic blind PARALIND algorithm whose performance is very close to nonblind space-time minimum mean square error (ST-MMSE) method. The blind PARALIND algorithm has the better performance than spacetime matched filter. The proposed PARALIND algorithm also works well in array error condition. Most notably, it does not require knowledge of the DOA (Direction Of Arrival) and channel fading information.
One-dimensional ternary photonic crystals are suggested as refractometric sensing elements, for sensing very small refractive index changes of a medium. These one-dimensional ternary photonic crystals based refractometric sensing elements are not only remarkably smaller, but are also more sensitive than one-dimensional binary photonic crystal based sensing element recently suggested by researchers.
The optimization and simulated realization of planar 2-D antenna array with a flat-top shaped-beam pattern are proposed in this paper. The shaped-beam planar array can be used as an element of Very Large Array for the Deep Space Detection. A conventional genetic algorithm is chosen for the optimization. However, the synthesis of flat-top shaped-beam using a planar 2-D array is difficult because of the inherently large number of degrees of freedom involved in the algorithm (in generally, the amplitude and phase of each element must be determined). Therefore, a sub-array rotation method, which lies on the flat-top pattern synthesis itself, is proposed in this study to resolve the design problem. Besides, the proposed synthesis has taken the actual element patterns but identical and isotropic ones into account, which can reduce the error between computation and realization. A 8*8 (64)-element rectangular array is exampled, and the results of the optimized flat-top patterns are shown to illustrate the validity and high efficiency of the technique.
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