514 research outputs found
Error analysis of the harmonics-based plane wave method
No full textInhomegeneous plane waves are used to represent 2D and 3D Green's functions in free space. A special sampling scheme allows a compensation between aliasing and truncation errors. An error model is provided for the 2D and 3D cases. Very high accuracy is obtained with very few points in spectral domain, which confirms the sub-Nyquist nature of the approach
Complex patterns devoted to physical compression of MoM matrices
No full textThe acceleration of Method-of-Moment (MoM) calculations often relies on compression of blocks of the MoM impedance matrix. This can be carried out algebraically, operating exclusively on lines and columns of the matrix. Here, we focus on physically-based compression techniques. Approaches based on multipole decompositions and on complex plane wave expansions are compared from the perspective of the rank of the interaction matrix and its dependence on distance. A drawback of the complex plane-wave expansion is mitigated by defining a set of patterns that can be reused when computing interactions between any pair of blocks. © 2013 EurAAP
Harmonics-Based Inhomogeneous Plane-Wave Method (HIPW)
No full textA formulation is presented for fast interactions between subdomains in two-dimensional (2-D) scattering problems. The formulation combines inhomogeneous plane waves with cylindrical harmonic decompositions of fields radiated by the subdomains. It is shown that the complexity of interactions naturally decays with the distance between subdomains and that very few elementary operations are involved at the lowest level. An example of iterative solution for scattering by a collection of cylinders validates the proposed approach
Statistics of the MLE and approximate upper and lower bounds-Part I: Application to TOA estimation
Get PDFIn nonlinear deterministic parameter estimation, the maximum likelihood estimator (MLE) is unable to attain the Cramér-Rao lower bound at low and medium signal-to-noise ratios (SNRs) due the threshold and ambiguity phenomena. In order to evaluate the achieved mean-squared error (MSE) at those SNR levels, we propose new MSE approximations (MSEA) and an approximate upper bound by using the method of interval estimation (MIE). The mean and the distribution of the MLE are approximated as well. The MIE consists in splitting the a priori domain of the unknown parameter into intervals and computing the statistics of the estimator in each interval. Also, we derive an approximate lower bound (ALB) based on the Taylor series expansion of noise and an ALB family by employing the binary detection principle. The accuracy of the proposed MSEAs and the tightness of the derived approximate bounds are validated by considering the example of time-of-arrival estimation
Multibeam and Beam Scanning With Modulated Metasurfaces
No full textMultibeam and beam-scanning capabilities of metasurface (MTS) antennas using multiple feeds are investigated. The MTS synthesis is performed by direct inversion of an electric field integral equation (EFIE) obtained after expanding the unknown equivalent impedance profile into Fourier-Bessel basis functions. Two approaches are explored. The first one assumes a priori a discrete azimuthal symmetry in the impedance profile, so as to constrain the solution to a subspace which automatically provides multiple beams when illuminated with feeds regularly arranged along azimuth. In the second approach, there are not a priori assumptions on the impedance profile, but the systems of equations corresponding to each beam are stacked and solved simultaneously in the least-squares sense. This second approach can also be used to obtain polarization diversity. More importantly, it also enables continuous beam scanning. The latter functionality is achieved through the generation of two embedded patterns in a common azimuthal window with opposite phase slopes, followed by a continuous phasing of the two feed points. Various designs are presented in this article. All the results are validated with the method of moments (MoM)
Numerically stable eigenmode extraction in 3-D periodic metamaterials
No full textA numerical method is presented to compute the eigenmodes supported by 3-D metamaterials using the method of moments. The method relies on interstitial equivalent currents between layers. First, a parabolic formulation is presented. Then, we present an iterative technique that can be used to linearize the problem. In this way, all the eigenmodes characterized by their transmission coefficients and equivalent interstitial currents can be found using a simple eigenvalue decomposition of a matrix. The accuracy that can be achieved is limited only by the quality of simulation, and we demonstrate that the error introduced when linearizing the problem decreases doubly exponentially with respect to the time devoted to the iterative process. We also draw a mathematical link and distinguish the proposed method from other transfer-matrix-based methods available in the literature
Multiple object tracking combining camera and radar
No full textAs the demand for accurate real-time multiple object tracking methods increases, the idea of developing a device combining multimodal sensors is proposed. This master thesis proposes an implementation of a pedestrian tracking algorithm based on a camera and a radar and explores the benefits and drawbacks of this type of setup. The intent behind this fusion is to combine the advantages of each of the sensors in order to gain accuracy in situations deemed challenging for methods making use of only one of the two sensors. The final solution uses a state-of-the-art 2D pedestrian detector to extract target positions from images taken by the camera and signal processing to extract observations from the radar. A particle filter is used to combine both information streams by primarily combining the azimuth angle as computed from camera detections with probable ranges observed by the radar. Its accuracy and precision are tested through a series of challenging tests. From the results, it is concluded that, while the camera offers accurate detection, angular localisation and appearance recognition it struggles with too large distance variations, which is why, in these situations, the use of a radar can be highly beneficial. Further improvements to the current method are also suggested for future worksMaster [120] : ingénieur civil mécanicien, Université catholique de Louvain, 201
Radiation Pattern of the SKALA antenna in the vicinity of a finite ground plane
No full textOne of the challenges regarding the SKA radio-telescope is the determination of the radiation pattern of the low frequency antenna in presence of a finite ground plane. In this Master Thesis, a methodology based on a spectral approach is built to calculate relatively fast the current induced in a finite ground plane placed under a given source. The field radiated by the source is estimated thanks to a method based on the decomposition into inhomogeneous plane waves and the current induced in the ground plane is calculated by solving a Method of Moments linear system of equations. The method is applied to the low frequency antenna of the SKA for different frequencies and ground plane diameters. The results are validated against the ones obtained with the EM simulation software FEKO.Master [120] : ingénieur civil électricien, Université catholique de Louvain, 201
On the connection between multiple-scattering based Macro Basis Functions and Krylov subspace methods
No full textA fast impedance and pattern computation scheme for finite antenna arrays
No full textA fast numerical method, well-suited to the analysis of moderate-size arrays made of complex elements, is presented. It combines macro basis functions and multipole approaches, without an iterative procedure. This method is exploited to estimate the impedance matrix and active element patterns. For the latter, an efficient formulation is provided, as a series of pattern multiplication problems. Examples are shown. for arrays of broadband dipoles. The computational gain obtained for the reduction of the original method of moments system of equations is briefly described
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