Light weight RLSAs with a honeycomb-type parallel plate are promising candidates for satellite antennas. However, the design of slot lengths and positions in honeycomb RLSAs consisting of a core, skin and adhesive layers involves time-consuming EM analysis. In this paper, an equivalent double layer model is devised for fast slot coupling analysis by the Method of moments (MoM) together with a simplified array design procedure. A fabricated antenna with a diameter of 900mm demonstrates the high directivity of 48.3dBi and a gain of 44.6dBi at 32GHz, with the reflection below -15dB. This antenna weighs only 1.16kg.

Metamaterials are generally defined as a class of artificial effective media which macroscopically exhibit extraordinary electromagnetic properties that may not be found in nature, and are composed of periodically structured dielectric, or magnetic, or metallic materials. This paper reviews recently developed electromagnetic modeling methods of metamatericals and their inherent basic ideas, with a focus on full wave numerical techniques. Methods described in this paper are the Method of Moments (MoM) and the Finite Difference Time Domain (FDTD) Method for scattering problems excited by an incident plane wave and a single nonperiodic source, and the Finite Element Method (FEM), the Finite Difference Frequency Domain (FDFD) method and the FDTD method for band diagram calculations.

Radiation integral areas are localized and reduced based upon the locality of scattering phenomena. In the high frequency, the scattering field is given by the currents, not the entire region, but on the local areas near the scattering centers, such as the stationary phase points and edge diffraction points, due to the cancelling effect of integrand in the radiation integral. The numerical calculation which this locality is implemented into has been proposed for 2-dimensional problems. The scattering field can be approximated by integrating the currents weighted by the adequate function in the local areas whose size and position are determined appropriately. Fresnel zone was previously introduced as the good criterion to determine the local areas, but the determination method was slightly different, depending on the type of scattering centers. The objective of this paper is to advance the Fresnel zone criteria in a 2-dimensional case to the next stage with enhanced generality and applicability. The Fresnel zone number is applied not directly to the actual surface but to the virtual one associated with the modified surface-normal vector satisfying the reflection law. At the same time, the argument in the weighting function is newly defined by the Fresnel zone number instead of the actual distance from the scattering centers. These two revisions bring about the following three advantages; the uniform treatment of various types scattering centers, the smallest area in the localization and applicability to 3-dimensional problems.

On the huge-scale array antenna for SSPS (space solar power systems), the problem of faulty elements and effect of mutual coupling between array elements should be considered in practice. In this paper, the effect of faulty elements as well as mutual coupling on the performance of the huge-scale array antenna are analyzed by using the proposed IEM/LAC. The result shows that effect of faulty elements and mutual coupling on the actual gain of the huge-scale array antenna are significant.

In this study, we demonstrate an acceleration of flexible generalized minimal residual algorithm (FGMRES) implemented with the method of moments and the fast multipole method (FMM), based on a combined tangential formulation. For the implementation of the FGMRES incorporated with the FMM concept, we propose a new definition of the truncation number for the FMM operator within the inner solver. The proposed truncation number provides an optimal variable preconditioner by controlling the accuracy and computational cost of the inner iteration. Moreover, to further accelerate the convergence, we introduce the concept of a multistage preconditioner. Numerical experiments reveal that our new version of FGMRES, based on the proposed truncation number for the inner solver and the multistage preconditioner, achieves outstanding acceleration of the convergence for large-scale and practical electromagnetic scattering and radiation problems with several levels of geometrical complexity.

In this letter, the reliabilty of the generalized normal-Laplace (GNL) distribution used for modeling the multiple access interference (MAI) plus noise in time-hopping (TH) binary phase-shift keying (BPSK) ultra-wideband (UWB) systems is evaluated in terms of the probability density function and the BER. The multiple access performance of TH-BPSK UWB systems based on GNL model is analyzed. The average BER performance obtained by using GNL approximation well matches with the exact BER results of TH-BPSK UWB systems. The parameter estimates of GNL distribution based on the moments estimation method is also presented.

A novel design technique for two-dimensional (2-D) waveguide slot arrays is proposed in this paper that combines a full-wave method of moments (MoM) analysis and an equivalent circuit with the explicit restraint of input matching. The admittance and slot spacing are determined first in an equivalent circuit to realize the desired distribution of power dissipation and phase, with the explicit restraint of input matching. Secondly by applying a full-wave MoM analysis to the finite 2-D array, slot parameters are iteratively determined to realize the active admittance designed above where slot mutual coupling and wall thickness are fully taken into account. The admittance, treated as the key parameter in the equivalent circuit corresponds to the power dissipation of the slots but not to the slot voltage, which is directly synthesized from the radiation pattern. The initial value of the power dissipation is assumed to be proportional to the square of the amplitude of the desired slot voltage. This assumption leads to a feedback procedure, because the resultant slot voltage distribution generally differs from the desired ones due to the effect of non-uniformity in the characteristic impedance on slot apertures. This slot voltage error is used to renew the initial distribution of power dissipation in the equivalent circuit. Generally, only one feedback cycle is needed. Two 2427-element arrays with uniform and Taylor distributions were designed and fabricated at 25.3 GHz. The measured overall reflections for both antennas were suppressed below -18 dB over the 24.3-26.3 GHz frequency range. High aperture efficiencies of 86.8% and 55.1% were realized for the antennas with uniform and Taylor distributions, the latter of which has very low sidelobes below -33 dB in both the E- and H-planes.

In this paper, the performance of the induced dimension reduction (IDR) method implemented along with the method of moments (MoM) is described. The MoM is based on a combined field integral equation for solving large-scale electromagnetic scattering problems involving conducting objects. The IDR method is one of Krylov subspace methods. This method was initially developed by Peter Sonneveld in 1979; it was subsequently generalized to the IDR(s) method. The method has recently attracted considerable attention in the field of computational physics. However, the performance of the IDR(s) has hardly been studied or practiced for electromagnetic wave problems. In this study, the performance of the IDR(s) is investigated and clarified by comparing the convergence property and memory requirement of the IDR(s) with those of other representative Krylov solvers such as biconjugate gradient (BiCG) methods and generalized minimal residual algorithm (GMRES). Numerical experiments reveal that the characteristics of the IDR(s) against the parameter s strongly depend on the geometry of the problem; in a problem with a complex geometry, s should be set to an adequately small value in order to avoid the "spurious convergence" which is a problem that the IDR(s) inherently holds. As for the convergence behavior, we observe that the IDR(s) has a better convergence ability than GPBiCG and GMRES(m) in a variety of problems with different complexities. Furthermore, we also confirm the IDR(s)'s inherent advantage in terms of the memory requirements over GMRES(m).

Method of moments (MoM) is an efficient design and analysis method for waveguide slot arrays. A rectangular entire-domain basis function is one of the most popular approximations for the slot aperture fields. MoM with only one basis function does not provide sufficient accuracy and the use of higher order mode of basis functions is inevitable to guarantee accuracy. However, including the higher order modes in MoM results in a rapid increase in the computational time as well as the analysis complexity; this is a serious drawback especially in the slot parameter optimization. The authors propose the slot correction length that compensates for the omission of higher order mode of basis functions. This length is constant for a wide range of couplings and frequency bands for various types of slots. The validity and universality of the concept of slot correction length are demonstrated for various slots and slot parameters. Practical slot array design can be drastically simplified by the use of MoM with only one basis function together with the slot correction length. As an example, a linear waveguide array of reflection-cancelling slot pairs is successfully designed.

Locality of high frequency electromagnetic scattering phenomena is embodied and imported to the Method of Moments (MoM) to reduce computational load. The proposed method solves currents on small areas only around inner and edge stationary phase points (SPPs) on the scatterer surfaces. The range of MoM area is explicitly specified in terms of Fresnel zone number as a function of frequency, source and observer positions. Based upon this criterion, scatterer of arbitrary size and shape can be solved with almost frequency independent number of unknowns. In some special cases like focusing systems, locality disappears and the method reduces to the standard MoM. The hybrid method called PO-MoM is complementarily introduced to cope with these cases, where Fresnel zone number with analogous but different definition is used. The selective use of Local-MoM and PO-MoM provides frequency insensitive number of unknowns for general combination of source and observation points. Numerical examples of RCS calculation for two dimensional flat and curved surfaces are presented to demonstrate the accuracy and reduction of unknowns of this method. The Fresnel zone, introduced in the scattering analysis for the first time, is a useful indicator of the locality or the boundary for MoM areas.

A novel computational method is proposed to investigate electromagnetic scattering problems. It is error controllable and reliable simulation in time domain can be performed. We apply the proposed method to analysis of transient scattering from open-ended structures and discuss scattering mechanisms.

This paper presents flexible inner-outer Krylov subspace methods, which are implemented using the fast multipole method (FMM) for solving scattering problems with mixed dielectric and conducting object. The flexible Krylov subspace methods refer to a class of methods that accept variable preconditioning. To obtain the maximum efficiency of the inner-outer methods, it is desirable to compute the inner iterations with the least possible effort. Hence, generally, inaccurate matrix-vector multiplication (MVM) is performed in the inner solver within a short computation time. This is realized by using a particular feature of the multipole techniques. The accuracy and computational cost of the FMM can be controlled by appropriately selecting the truncation number, which indicates the number of multipoles used to express far-field interactions. On the basis of the abovementioned fact, we construct a less-accurate but much cheaper version of the FMM by intentionally setting the truncation number to a sufficiently low value, and then use it for the computation of inaccurate MVM in the inner solver. However, there exists no definite rule for determining the suitable level of accuracy for the FMM within the inner solver. The main focus of this study is to clarify the relationship between the overall efficiency of the flexible inner-outer Krylov solver and the accuracy of the FMM within the inner solver. Numerical experiments reveal that there exits an optimal accuracy level for the FMM within the inner solver, and that a moderately accurate FMM operator serves as the optimal preconditioner.

The conjugate gradient-fast multipole method (CG-FMM) is one of the powerful methods for analysis of large-scale electromagnetic problems. It is also known that CPU time and computer memory can be reduced by CG-FMM but such computational cost of CG-FMM depends on shape and electrical properties of an analysis model. In this paper, relation between the number of multipoles and number of segments in each group is derived from dimension of segment arrangement in four typical wiregrid models. Based on the relation and numerical results for these typical models, the CPU time per iteration and computer memory are quantitatively discussed. In addition, the number of iteration steps, which is related to condition number of impedance matrix and analysis model, is also considered from a physical point of view.

A novel analysis model for post-wall waveguide T-junctions is proposed. Equivalent solid-walls for the post-walls to have equal guided wavelength are corrected in the analysis model so that the wall thickness for the coupling windows is set to the difference in the width between the post-wall and the solid-wall waveguides. The accuracy of the proposed model is confirmed by comparing it to an HFSS analysis for the real structure of the post-wall waveguide T-junction including the post surfaces. 61.25 GHz model antennas are fabricated for experimental verification. The reflection of the antenna designed by the modified analysis model is suppressed to below -15 dB over a 5.6 GHz bandwidth, while that in the antenna designed by the conventional model is larger than -15 dB around the design frequency.

In this paper the SNR estimation is performed frame by frame, during the speech activity. For this purpose, the fourth-order moments of the real and imaginary parts of frequency components are extracted, for both the speech and noise, separately. For each noisy frame, the mentioned fourth-order moments are also estimated. Making use of the proposed formulas, the signal-to-noise ratio is estimated in each frequency index of the noisy frame. These formulas also predict the overall signal-to-noise ratio in each noisy frame. What makes our method outstanding compared to conventional approaches is that this method takes into consideration both the speech and noise identically. It estimates the negative SNR almost as well as the positive SNR.

An extreamly large scale periodic array antenna is required for transmitting power from space solar power systems. Analysis of the huge-scale array antenna is important to estimate the radiation property of the array antenna, but a full-wave analysis requires too much computer memory and excessive CPU time. In order to overcome these difficulties, the impedance extension method is proposed as a method of approximate analysis for huge periodic array antennas. From the results of actual gain pattern obtained by the proposed method and its relative error, it is shown that edge effects of a huge-scale array antenna can be ignored in calculating the radiation property.

In this paper, a design method of two-dimensional (2-D) orthogonal symmetric wavelets is proposed by using a lattice structure for multi-dimensional (M-D) linear-phase paraunitary filter banks (LPPUFB), which the authors have proposed as a previous work and then modified by Lu Gan et al. The derivation process for the constraints on the second-order vanishing moments is shown and some design examples obtained through optimization with the constraints are exemplified. In order to verify the significance of the constraints, some experimental results are shown for Lena and Barbara image.

The purpose of this study is the real-time estimation of Doppler spectral moments for precipitation in the presence of ground clutter overlap. The proposed method is a frequency domain approach that uses a Gaussian model both to remove clutter spectrum and to estimate weather spectrum. The main advantage of this method is that it does not use processes like several fitting procedures and enables to estimate profiles of precipitation in a short processing time. Therefore this method is efficient for real-time radar observation with high range and time resolution. The performance of this method is evaluated based on simulation data and the observation data acquired by the Ku-band broad band radar (BBR) [1].

An explicit expression for the impulse response coefficients of the predictive FIR digital filters is derived. The formula specifies a four-parameter family of smoothing FIR digital filters containing the Savitsky-Goaly filters, the Heinonen-Neuvo polynomial predictors, and the smoothing differentiators of arbitrary integer orders. The Hahn polynomials, which are orthogonal with respect to a discrete variable, are the main tool employed in the derivation of the formula. A recursive formula for the computation of the transfer function of the filters, which is the z-transform of a terminated sequence of polynomial ordinates, is also introduced. The formula can be used to design structures with low computational complexity for filters of any order.

In this paper, a novel independent component analysis (ICA) approach is proposed, which is robust against the interference of impulse noise. To implement ICA in a noisy environment is a difficult problem, in which traditional ICA may lead to poor results. We propose a method that consists of noise detection and image signal recovery. The proposed approach includes two procedures. In the first procedure, we introduce a self-organizing map (SOM) network to determine if the observed image pixels are corrupted by noise. We will mark each pixel to distinguish normal and corrupted ones. In the second procedure, we use one of two traditional ICA algorithms (fixed-point algorithm and Gaussian moments-based fixed-point algorithm) to separate the images. The fixed-point algorithm is proposed for general ICA model in which there is no noise interference. The Gaussian moments-based fixed-point algorithm is robust to noise interference. Therefore, according to the mark of image pixel, we choose the fixed-point or the Gaussian moments-based fixed-point algorithm to update the separation matrix. The proposed approach has the capacity not only to recover the mixed images, but also to reduce noise from observed images. The simulation results and analysis show that the proposed approach is suitable for practical unsupervised separation problem.