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We present the results of an efficient analysis–based on adaptive network fuzzy inference systems (ANFIS)–of the impedance an infinite array of rectangular microstrip antennas. In the proposed modeling approach, first, a number of input–output pairs (inputs include spacing between antennas, outputs include resonant frequency, quality factor, and input resistance) are computed from full-wave methods, and they are then used in the training process. An advantage of the proposed model in comparison with full-wave and approximate methods is that, after convergence of the training process, it bypasses the repeated use of complex computations for new inputs presented to it without any restriction. In addition, a comparison of the proposed model with those related to a single rectangular microstrip antenna shows considerable differences, especially for input resistance and quality factor, which is of importance in practical applications. [ABSTRACT FROM AUTHOR]

In this paper, different arrangements of infinite arrays of nonlinearly loaded antennas are analyzed in the frequency domain by an efficient approximate method and compared with the exact one which are respectively based on the nonlinear current and harmonic balance techniques. In one hand, although the exact method is suitable for strongly nonlinear load, it is suffering from gradient operation and initial guess in the iteration process especially under multi-tone excitations. On the other hand, although the approximate method is very efficient, it is limited to weakly nonlinear loads and low-valued incident waves. Finally, acceptable ranges for application of the approximate method versus different parameters such as nonlinearity effect of the load and the magnitude of incident wave are extracted.

This work presents an analytic model to derive the scan impedance of planar infinite phased arrays of dipoles at a dielectric interface when only the (0, 0) Floquet mode propagates. The proposed model builds on the boundary conditions met by the fundamental Floquet mode at the interface to provide a novel derivation of the equivalent circuit for the scan impedance. The analysis is also extended to include the effect of a sufficiently thick grounded substrate that does not affect the elements’ current distribution and does not interact with the evanescent fields. Next, formulas for the ratio of intensity radiated toward each half-space for an interfacial array are provided. In a consecutive step, an asymptotic approximation is derived for the current distribution in arrays of arbitrary loaded dipoles, and the reactance of a dipole in the array environment is related to the inductance of a grid of wires. This model constitutes a useful tool to clearly identify the role of the different array variables (dipole dimensions, relative permittivity of the substrate, periodicity, end load, and scan angle in the principal planes) on the scan impedance by simple expressions and equivalent circuits. The model predictions are in good agreement with full-wave simulations and with previously published works. [ABSTRACT FROM AUTHOR]

The problem of infinite array of slot impedance loads with dielectric coating excitation by plane wave is considered with the purpose of determining the equivalent surface impedance. Each array element consists of three areas and The area is the half space above the delimiter boundary. In this area the primary field is excited by the plane wave. The area does not contain any excitation sources and consists of dielectric layer of t thickness located between the planes and The area does not contain any excitation sources either and is bounded by parallel-plate waveguide walls with the distance b between them. The area is connected with the area by one or several slots in the top wall of the parallel-plate waveguide placed on the boundary of volumes and . A plane conductor is placed in the aperture of each slot. Excitation source characteristics and construction parameters do not depend on z coordinate (2D-problem). The problem is solved by the integral equation method and is calculated by the Krylov-Bogolyubov method so that the integral equation is reduced to the system of linear algebraic equations. To overcome mathematical difficulties dealing with logarithmic singularity in the kernel of the integral equation Kummer transformation is used. This allows not only improving the series convergence but also getting the logarithmic singularity in explicit form and integrating it analytically. Numerical results are given as equivalent surface impedance dependencies on the construction geometrical dimensions for fixed values of the averaging interval, the plane wave incidence angle and the thickness of the dielectric layer. It is shown that equivalent surface impedance can be varied by changing the slot width and the plane conductor width. A comparative analysis of the obtained dependencies possessing impedance load characteristics with no dielectric coating is carried out.

The problem of infinite array of slot impedance loads excitation by plane wave is considered in order to determine the equivalent surface impedance. Each array element is an aperture in the wall of parallel-plate waveguide. A plane conductor is placed in the aperture. Fields representation as expansion in Floquet harmonics was used, the solution is reduced to integral equation calculated by the Krylov-Bogolyubov method. Numerical results are obtained as an equivalent surface impedance dependency on the aperture size, strip conductor size in the aperture and on the plane wave incidence angle. A comparative analysis of obtained dependencies with single impedance load characteristics is carried out.

A nonstandard Schwarz domain decomposition method is proposed as finite-element mesh truncation for the analysis of infinite arrays. The proposed methodology provides an (asymptotic) numerically exact radiation condition regardless of the distance to the sources of the problem and without disturbing the original sparsity of the finite-element matrices. Furthermore, it works as a multi Floquet mode (propagating and evanescent) absorbing boundary condition. Numerical results illustrating main features of the proposed methodology are shown. [ABSTRACT FROM AUTHOR]

We address the task of modelling numerically turbulent flows within random arrays of circular cylinders, relevant for several industrial and environmental applications. Numerical simulations are employed to model infinite domains of randomly placed emergent and rigid cylinders validated by a laboratory database acquired by a PIV system. The main goals are: (i) to discuss the effect of the numerical domain size and the grid resolution on the first and second order moments; and (ii) to characterise the spatial distribution of mean flow and turbulence variables in the drag-wake controlled stratum. Five domains of different sizes (9–44 cylinders) and four grid resolutions were independently tested. The results show that the time-averaged velocity field and the Reynolds stress tensor were not significantly affected by the size of the tested numerical domains. The analysis of the grid resolution influence shows how the results improve with mesh refinement, while none of the tested meshes produces un-physical results. The present work provides guidance on the acceptable compromises, in terms of mesh resolution and domain size, when predicting, with eddy resolving computational fluid mechanics tools, first and second-order moments of turbulent flows within infinite arrays or randomly placed cylinders. [ABSTRACT FROM AUTHOR]

In this paper, analysis of free-standing periodic array of thin conducting strips using waveguide simulator is presented. The method of moment is applied to numerically obtain its scattering parameters. With only two elements inside the waveguide simulator, scattering response of the infinite array illuminated by plane waves is accurately achieved. Coupled integral equations, due to the presence of two elements, are solved using pulse expansion and point matching technique. Numerically obtained results are compared with waveguide and plane wave simulations in CST MWS and measurement results for validation. [ABSTRACT FROM AUTHOR]

A novel method for the analysis of an infinite array with a rectangular lattice geometry, which involves treating the space above the plane of the array with methods derived from the theory of classical microwave waveguides, is proposed. The equations demonstrated in this work, were implemented into computer codes which were subsequently employed for modeling the behavior of the array while scanned over the free half-space. The parameters calculated by the computer codes are in good agreement with the results provided by other methods. [ABSTRACT FROM AUTHOR]

This work proposes an efficient optimization methodology of antenna array excitations accounting for the effects of mutual couplings and real radiating patterns of array elements with complex geometry. The method is formulated as a linear programming problem providing multibeam patterns with specified beamwidths, constraints on sidelobe and cross-polar levels, and null pointing directions. A matrix formulation is used to integrate the optimization procedure and a finite-array analysis based on the infinite-array approach, in which the periodic radiating element is characterized by a full-wave and hybrid procedure, combining the domain decomposition technique, the finite-element method, and modal analysis. Numerical examples of arrays of open-ended waveguides, microstrip antennas, and dielectric resonator antennas are presented. [ABSTRACT FROM PUBLISHER]

The effect of dielectric substrate on the performance of infinite arrays of single-polarized Vivaldi antennas is studied by computing the input impedance of an antenna in an array environment by using full wave method of moments techniques. It is found that dielectric permittivity plays an important role in the wideband performance of such arrays, and comparison with dielectric-free cases for similar geometries is also included to bring out the impact of the substrate. In particular, increasing dielectric permittivity improves the bandwidth considerably (bandwidth up to 10:1 is predicted). The parametric variation due to permittivity is presented in detail, and optimization involving other design parameters is discussed. Results from a parallel plate waveguide simulator technique employed to assess and compare the array performance of Vivaldi with different dielectric permittivities qualitatively support the predicted effect of dielectric substrate. [ABSTRACT FROM PUBLISHER]

A new subclass of infinite arrays, called hv-local infinite arrays, is introduced. We prove that recognizable infinite arrays are projections of hv-local infinite arrays. We provide automata characterization to the class of hv-local infinite arrays, by introducing online tesselation local automata. A learning algorithm in the limit from positive data for the class of hv-local infinite arrays is given. [Copyright &y& Elsevier]