A method of moments model for VHF propagation

Predictions of a numerical model for site specific very high frequency (VHF) propagation over irregular terrain are compared to experimental data and to other propagation models. The numerical model is based on an iterative version of the method of moments (MOM) known as the banded matrix flat surface iterative approach (BMFSIA) for either perfectly conducting or penetrable surfaces rough in one direction only. Due to the large size of the numerical problem (65000 to 130000 unknowns), a parallel implementation of the method is presented and applied in the simulations. Comparisons with measurement data show good agreement overall and also illustrate the sensitivity of the model to input terrain profiles. Comparisons with other propagation models show good agreement also in cases where these models are expected to be valid and further clarify the limitations of the approximations made in these methods     

Analysis of nu-dipole antennas using the method of moments

An analysis of the features of a novel antenna, the nu-dipole, is presented and its input characteristics compared with those of the vee-dipole antenna. By adapting the thin-wire approximation, the integro-differential equation formulated for the nu-dipole antenna problem is converted into a matrix equation by using the moment method based on Galerkin's procedure, in which the current expansion and testing functions are both triangle functions. Upon employing known matrix methods the current distribution on the antenna emerges from the solution of the matrix equation. Based on the obtained current distribution, the input admittance and power are evaluated and compared with those of the vee-dipole. For these results, the nu-dipole possesses higher amplitudes but at slightly higher resonant electrical lengths. The nu-dipole far-zone electric field pattern |E _θ(θ,φ = 90°)| rotates as the electrical length is varied.     

Determination of time-of-flight surfaces using the method of moments [US imaging

To produce an image from backscattered signals requires a knowledge of the time of flight from each source to each sensor in a transducer array. The authors reduced the determination of the rectangular coordinates of a new point on any time-of-flight surface, which requires finding the square root of the sum of squares, to the time of a single addition. To do this, the time-of-flight surface was represented by a two-dimensional, positive-integer-degree polynomial and then that polynomial was implemented in its forward-difference form. Two solutions for such a polynomial were found using the method of moments. A minimum-mean-square-error constraint yields polynomial coefficients from a numeric evaluation of the moments of arbitrary surfaces over rectangular regions, and an analytical solution for moments of time-of-flight surfaces over sector-shaped regions. For a 7x6-cm region at a minimum range of 4 cm centered in a 74 degrees sector, the maximum error for a second-degree polynomial was 0.30% of the average time of flight over the region for the numeric solution and 0.32% for the analytic solution, assuming a 1500-m/s background velocity.     

基于改进离散Green函数的字符矩的计算方法

图像矩及其不变量是图像处理和图像识别的一个重要工具。高阶矩的计算会对计算效率产生影响。利用离散Green函数可以实现降维操作,文中提出一种改进的离散Green函数矩计算算法,消除左右端点配对的要求,适应于任意多连通区域,并且大幅度提高了算法的执行速度,利用边界标定自动机方法,对边界像素进行跟踪和标记,避免重复扫描,得到边界像素,结合改进的离散Green函数方法完成对图像中所有字符矩的计算工作。     

Optimization technique for linearly polarized radial-line slot-array antennas using the multiple sweep method of moments

This paper presents an effective full-wave procedure to optimize linearly polarized radial-line slot-array antennas. The procedure is based on a recursive method for solving large matrix equations known as the multiple sweep method of moments. As a result of this paper, new design suggestions have been introduced which greatly contribute to the performance improvement of this type of antennas. These elements are the arrangement of the slots in concentric ellipses instead of circles and a slight but crucial modification on the usual collocation of the reflection-canceling slots.     

Some remarks on Nakagami-m parameter estimation using method of moments

This letter develops new estimators for the Nakagami-m parameter based on real (integer and fractional) sample moments. These moment-based estimators are asymptotically unbiased, efficient, and have lower computational budget compared to the best known integer and real moment estimators [Cheng, J et al., (2002), Eqs. (4) and (9)] but comparable to [Gaeddert, J et al., (2005), Eq. (5)]. Specifically, the asymptotic expansion of sample moments derived in this article provides a generalized closed-form expression for the Nakagami-m parameter without the need for coefficient optimization for different ratios of real moments as needed in [Gaeddert, J et al., (2005)].     

Study of antennas in reverberation chamber using method of moments with cavity Green's function calculated by Ewald summation

A numerical model of wires in rectangular metal cavities is introduced for computing antennas in a simplified theoretical reverberation chamber. The code is based on the method of moments, and it uses the Ewald summation for efficient calculation of the cavity Green's function. The Q-value of the chamber is accounted for in the model by a homogeneous material filling the chamber. The S-parameters of two dipoles placed in many random positions in the cavity are computed and averaged to provide the average transfer function of the chamber. This represents mode stirring by moving the antennas, referred to as position stirring. The computed results are compared with theoretical statistical values as well as experimental results. The discrepancies are discussed.     

Numerical modeling of dielectric-resonator antennas in a complexenvironment using the method of moments

Aperture coupled dielectric resonator antennas (DRAs) that reside above a layered background are analyzed using the method of moments (MoM). Dyadic Green's functions for the layered medium are derived in a simple and effective manner and the Rao-Wilton-Glisson (RWG) function is used to expand both electric and magnetic currents. A transmission-line technique is used to compute the antenna-input impedance. Numerical results obtained for both hemispheric and rectangular DRAB agree well with published measurement results     

Modifications to the method of moments

A modification to the standard moment procedure is proposed for thin-wire aerials of arbitrary shape. Using a homogeneous form and 2nd-order approximations, a normalised current can be obtained, from which the impedance is calculated by integration of the near fields.     

On minimal realization of transfer function matrices using Markov parameters and moments

An algorithm is presented for obtaining a minimal order realization from a given rational transfer function matrix using the combination of Markov parameters and moments. The technique requires construction of modified Hankel matrix and then its transformation to Hermite normal form using outer products. The realization can be achieved in fixed number of operations on the Hankel matrix. The proposed algorithm is computationally better than the existing methods.     

Voltage transfer function synthesis using current conveyors

A synthesis procedure for generating current conveyor active filters is presented, and a novel network which realises the general 2nd-order voltage transfer function is given.<>     

Numerical analysis of travelling wave structure using hybrid basisfunctions in the method of moments

A new model is presented to improve the computational efficiency of analysing large travelling wave antennas: such as leaky wave antennas using the method of moments (MoM). The method uses a new type of travelling wave basis function which interfaces seamlessly with the rooftop sub-domain basis function. The computation time and resources are significantly economised by reducing the size of the matrix     

Raindrop size distribution using method of moments for terrestrial and satellite communication applications in Singapore

As communication services using higher frequencies are growing rapidly in the tropics, there is an increasing need for a finer model to predict the attenuation due to rain. The raindrop size distribution (DSD) is one of the major sources of error in any prediction model, mainly because of its variability in both space and time. The DSD parameters are computed from distrometer data that are classified into stratiform and convective types using S-band radar data. The method of moments is employed to estimate the parameters of lognormal DSD. The modeled DSD parameters are optimized by examining the root mean square (RMS) error and the average probability ratio (APR) in estimation of the rain rate, rain attenuation, and radar reflectivity factor simultaneously. The proposed model gives maximum (close to unity) APR and minimum RMS error when compared to any other set of DSD parameters.     

Extraction of network parameters in the electromagnetic analysis ofplanar structures using the method of moments

Integration of electromagnetic (EM) and circuit analyses for the modeling of spatially distributed microwave and millimeter-wave circuits requires the establishment of ports that are defined in both the circuit and EM realms. Four EM techniques are developed here and contrasted for the extraction of the port network parameters at circuit compatible ports. A full-wave method of-moments EM analysis directly yielding network parameters of a slot-stripline-slot structure is formulated     

A multiresolution method of moments for triangular meshes

This paper presents the construction, use, and properties of a multiresolution (wavelet) basis for the method of moments (MoM) analysis of metal antennas, scatterers, and microwave circuits discretized by triangular meshes. Several application examples show fast convergence of iterative solvers and accurate solutions with highly sparse MoM matrices. The proposed basis is organized in hierarchical levels, and keeps the different scales of the problem directly into the basis functions representation; the current is divided into a solenoidal and a quasi-irrotational part, which allows mapping these two vector parts onto fully scalar quantities, where the wavelets are defined. As a byproduct, this paper also presents a way to construct hierarchical sets of Rao-Wilton-Glisson (RWG) functions on a family of meshes obtained by subsequent refinement, i.e., with the RWG of coarser meshes expressed as linear combinations of those of finer meshes.     

Full-wave analysis of coupled lossy transmission lines using multiwavelet-based method of moments

Full-wave analysis for coupled lossy transmission lines with finite thickness is conducted using a multiwavelet-based method of moments (MBMM). We use the multiscalets with multiplicity r=2 as the basis and testing functions, and take the discrete Sobolev-type inner products to discretize the integral equation and its derivative at the testing points. Since the numerical integration is not needed in the testing procedure, the new approach is faster, yet preserves high accuracy due to the derivative sampling. In the new approach, we compute the incoming fields in the spatial domain directly without resorting to the inverse Fourier transform. Hence, the local coordinate system used to perform the Sommerfeld integral is avoided and the computational cost is reduced remarkably. In addition, a coarser mesh can be used owing to the smoothness of the multiscalets. Numerical examples show that the MBMM speeds up the traditional method of moments 3 /spl sim/ 10 times.     

Novel method for realising lossless floating immittance using current conveyors

A novel method for realising lossless floating immittance using second-generation current conveyors (CCIIs) is proposed. By introducing the nullator-norator technique, many simulation circuits can be derived systematically.     

Modeling baluns with the method of moments

When using the method of moments (MoM) to model large arrays with large numbers of balanced feeds, the feed baluns can always be incorporated into the analysis by combining the multiport admittance matrix for the array with the admittance matrices of the baluns. This technique is straightforward but requires that the MoM equations be solved for a large number of right-hand sides. The paper shows how the effects of perfect baluns can be incorporated directly into the MoM equations, requiring only one right-hand side. This technique yields the exact results with a significant savings in computing resources     

Minimal realisation of a symmetric transfer function matrix using Markov parameters and moments

An algorithm for determining a minimal realisation from a symmetric transfer function matrix using a combination of Markov parameters and moments has been proposed. The procedure seems preferable for the problem of identification, when only a few Markov parameters are available.