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In the context of the optimization of a versatile type of metasurface consisting of intertwined spirals printed on a dielectric substrate and loaded with discrete impedances, we propose a simple development of the method of moments interaction matrix that allows obtaining the scattered field almost instantly for any distribution of discrete loads. Simulation results for a sample design are presented...
Frequency-domain Method of Moments (MoM) is a mature numerical technique that is formulated in the frequency domain, as opposed to time-domain methods. For that reason, computation time can increase rapidly when results are required over a large number of frequencies. This is also true when material properties are varied. In this paper, we show that rapid computation of the impedance matrix for various...
Fast methods for the evaluation of the EFIE operator at a given current distribution undergo some difficulties at low frequency. In particular, it is well known that the MLFMA at low frequency undergoes a breakdown due to the translation operator that becomes unstable. In this paper, an innovative method that provides a fast way to calculate the evaluation of the EFIE operator at a given current distribution...
The Square Kilometre Array — Aperture Array Mid-frequency instrument will be part of the largest next generation radio telescope. To meet the scientific requirements while maintaining a lower number of antenna elements, the University of Cambridge is developing a sparse random array solution using log-periodic dipole array antennas. In this paper we present the application of HARP, a numerical method...
A reflect-type metasurface with phase gradient discontinuity is proposed. It is formed by planar intertwined spiral conductors loaded with inductors. A pattern of conductors is initially designed under the assumption of locally periodicity and the phase response of uniform arrays. Simulations are performed with a fast proprietary code based on the periodic Method of Moment and the Array Scanning Method...
The full-wave simulation of semi-infinite metamaterials is a key tool to the understanding of surface-bounded wave phenomena. In this paper, we present a method that can be used to model a semi-infinite metamaterial using full-wave simulations based on the Method of Moments. First, the impedance matrices describing one layer of the metamaterial are transformed in order to obtain the response of a...
Closed-form analytical expressions are derived for the numerical integration of the spectral Green's function with Contour-FFT. Results indicates that a proper uniform grid of spatial points enhances the convergence rate of the truncation error, that the Nyquist-Shannon theorem can be generalized to inverse Laplace transforms on linear path and that the relative error specific to Contour-FFT is a...
A fast method for the radiation analysis of arbitrary oriented planes is presented. It combines an adaptive spectral integration scheme and a recently proposed unequally-spaced fast Laplace transform algorithm [F. Andersson, “Algorithms for Unequally Spaced Fast Laplace Transforms,” Applied Computational Harmonic Analysis, vol. 35, pp. 419–432, 2013]. It is illustrated on the free-space Green's function...
Full-wave simulations of 2D periodic arrays using the Method of Moments (MoM) are investigated. A method based on plane wave decomposition is used to fill the MoM impedance matrix. For pair of basis and testing functions that are close to each other, a singular term is removed before extrapolating the value of the impedance matrix using a Taylor expansion. The two main advantages of this method are...
Krylov subspace iterative techniques consist of finding the solution of a scattering problem as a linear combination of “generating vectors” obtained through successive matrix-vector multiplications. This letter extends this approach to domain-decomposition. Here, on each subdomain, a subspace is obtained by constructing the segments of each generating vector associated with the subdomain and by weighting...
This paper focuses on the direct computation of the interactions between the Macro Basis Functions (MBFs) defined on distinct sub-domains using their complex patterns. They are computed using a set of inhomogeneous plane waves, which can be viewed as an extension of the Fast Inhomogeneous Plane Wave Algorithm (FIPWA), using a new spectral-domain sampling. Examples of slot antennas and 3D frustum array...
The Physical Optics aperture radiation is decomposed into an inhomogeneous plane-wave spectrum, for which a sub-nyquist sampling is achieved, despite a 2-digits accuracy. Validation with a Hertzian dipole and observations are made for large planar surfaces. The Spectral Physical Optics (SPO) seems particularly well-suited for multiple interactions between large facets in complex scattering environnements.
The low-frequency instrument of the SKA radiotelescope will be made of large arrays of log-periodic antennas. Their mutual coupling may be strong and needs to be modeled in terms of embedded element patterns. The HARP method is based on Macro Basis Functions and computes their interactions versus relative positions, based on a limited number of explicit calculations in the near field. This paper shows...
The orthogonality properties of the eigenmodes inside 2D periodic structure such as the wire medium are investigated. We propose a scalar product for which eigenmodes are orthogonal if the material has no losses. Prospective applications such as accuracy check or quasi-analytical solution of scattering problems are suggested.
Modeling the electromagnetic behaviour of metamaterials is a challenge that is still being addressed. The computation of the propagative modes inside the materials is necessary to understand the way periodic structures interact with electromagnetic fields and to develop methods to characterize them. In this paper, we present a numerical method based on the PMCHWT formulation of the Method of Moments...
We present a post-compression method based on the Singular Value Decomposition that can be used to retrieve the low-rank representation of the Method of Moments interaction matrix after using the shielded-block preconditioner. A compression ratio of more than 17 has be achieved without significant loss of accuracy. The time needed to compress the preconditioned matrix is negligible with respect to...
In this paper the effect of local variability of soil moisture within the antenna footprint on GPR data is studied. A combination of GprMax3D with GPR full-wave model of Lambot and André (2013) is used for an errorless set of measurements. The GprMax3D simulations are used as real GPR measurements regarding several physical-based configurations. The Greens functions of the simulated data are extracted...
A technique is presented for the efficient analysis of finite printed antenna arrays made of identical elements. A multipole expansion can be obtained for planar layered medium GFs, and exploited to provide a fast evaluation of the reaction integrals between the Macro Basis Functions used to compress the original problem after decomposing it into subdomains (the array elements). The computational...
The design and fabrication of an ultrawideband (UWB) imaging radar system for near-field applications is presented. First, the geometric parameters related to the elliptical curve of Vivaldi antenna, i.e. major and minor radii and center, are introduced as additional design parameters. Second, the complete circular UWB radar imaging system is fabricated. Finally, time-domain responses of a target...
Modern aperture array radio-telescopes at MHz frequencies (like the SKA-low instrument) will be made of a very large number of wideband antennas possibly arranged in an irregular configuration, with many imperfections to be corrected for, like mutual coupling. Here, low-order beam representations of array beams are given by using simulated embedded element radiation patterns, multiplied by low-order...
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