Jesús Rubio

Generalized-scattering-matrix analysis of a class of finite arrays of coupled antennas by using 3-D FEM and spherical mode expansion

A rigorous method for characterizing, in terms of a multimode scattering matrix, a finite array of antennas where each antenna can be described by means of spherical waves is presented in this paper. The procedure provides the impedance, coupling and radiating characteristics of the arrays and comprises two steps. First, the generalized scattering matrix (GSM) of each single antenna is numerically calculated over a wide band of frequencies. For this purpose we use a previously-developed methodology that combines the domain segmentation technique, the three-dimensional finite element method (3D-FEM), spherical mode expansion and a reduced order model obtained using a symmetric matrix Pade/spl acute/-Via-Lanczos (SyMPVL) algorithm. Second, the overall GSM of the finite array is calculated starting from the GSM of each antenna and using rotation and translation of spherical waves. A closed-form expression for the overall GSM is given and different examples are shown in order to validate the proposed method.

Analysis of cavity-backed microstrip antennas by a 3-D finite element/segmentation method and a matrix Lanczos-Pade algorithm (SFELP)

A methodology that combines the domain segmentation technique, the three-dimensional finite-element method (3-D FEM), and a symmetric matrix Lanczos-Pade algorithm, is used for the fast frequency-sweep analysis of cavity-backed microstrip antennas by using a spherical mode expansion on the radiation boundary. Results for a circular patch antenna validate the proposed method.

A CAD-oriented method to analyze and design radiating structures based on bodies of revolution by using finite elements and generalized scattering matrix

In this work, an efficient analysis of radiating structures based on bodies of revolution is dealt with. The procedure is a hybrid method based on a segmentation of the structure into two-dimensional regions, finite elements and a spherical computation domain surrounding the antenna, defining a boundary or port where a spherical mode expansion of the fields is used. A reduced order model is computed for a fast frequency sweep. To validate this method, some structures based on bodies of revolution as a rod dielectric antenna, conical dielectric-loaded horns, profiled horns and a monopole-dielectric resonator antenna are studied and results are compared with those demonstrated by other authors. The design of a smooth-walled horn by means of the optimization of the profile is also carried out

Efficient full-wave analysis of mutual coupling between cavity-backed microstrip patch antennas

A full-wave methodology for a broadband analysis of isolated cavity-backed and probe-fed arbitrarily shaped microstrip patch antennas is combined with an analytical method based on the properties of rotation and translation of spherical modes for obtaining an efficient scattering matrix description of the mutual coupling in a two-element array. The proposed procedure is validated and results are given for identical circular cavity-backed patch antennas.

ANN Characterization of Multi-Layer Reflectarray Elements for Contoured-Beam Space Antennas in the Ku-Band

The analysis of a 1.2-meter, contour-shaped reflectarray antenna through the use of Artificial Neuronal Networks (ANNs) is carried out in this paper. The analysis is a two-step procedure: reflectarray element modeling and pattern synthesis. In the first step, artificial neural networks are found to reproduce both the amplitude and the phase of the complex reflection coefficient of the three-layered reflectarray element. For this task, up to 9 free input parameters are considered: six geometrical parameters, the incident angle in terms of azimuth, θ, and elevation, φ, and the frequency. Because of this large number of free parameters, a new artificial neural network training methodology has been developed regarding both the training set and the training process itself. In the second step, extensive full wave electromagnetic computation is replaced by trained artificial neural networks to calculate the electric field on the planar structure and the radiation pattern. A good agreement is obtained compared to an analogous analysis carried out by Method of Moments. Thanks to this methodology, the speed up factor in terms of time is in the order of 7×102, which represents a significant improvement in Computer Aided Design (CAD) of reflectarray antennas.

Inclusion of the Feeding Network Effects in the Generalized-Scattering-Matrix Formulation of a Finite Array

The formulation of the generalized scattering matrix (GSM) of a finite array is revised to take into account the feeding network effects in the calculation of the external mutual coupling. It allows the analysis of finite arrays of externally coupled elements whose radiated field can be described by means of spherical waves on a ground plane, such as apertures, monopoles, cavity-backed patch antennas, or dielectric resonator antennas (DRAs), including rigorously the mismatching and internal coupling effects because of the feeding network.

Mutual Coupling Compensation Matrices for Transmitting and Receiving Arrays

A general method to obtain a matrix which allows the compensation of mutual coupling effects in transmitting arrays for the total field in all directions is introduced. This method is independent of the numerical method used in the analysis and it can include the effect of the antenna platform. The starting point can be the active element patterns or the spherical mode expansion from spherical near-field antenna measurements. Additionally, the spherical mode expansion is also used to find a matrix which allows the compensation of mutual coupling effects in receiving arrays. Through this theory, a simple relation between the compensation matrices of the transmitting and the receiving arrays is found. As a consequence, the scattering matrix of a circuit that allows the simultaneous compensation of mutual coupling effects for the transmission and the reception problem can be easily defined. Finally, it will be shown how the capabilities of the compensation in all directions depend strongly on the array element.

Multiobjective Optimization of Real and Coupled Antenna Array Excitations via Primal-Dual, Interior Point Filter Method From Spherical Mode Expansions

A novel method for the multiobjective optimization of arbitrary planar array excitations is presented. The optimization problem formulation, which inherently takes into account every array element pattern as well as all interelement couplings, is based on matrix-valued functions which are computed from the generalized-scattering-matrix characterization of an array and spherical mode expansions of its radiated field. It allows the maximization of the directive gain subject to a maximum sidelobe level, a maximum crosspolar level and a minimum aperture illumination efficiency, the setting of null-pointing directions and the dynamic range control. To solve the resulting non-linear optimization problem, we have developed a primal-dual interior point method specifically adapted to the presented formulation, which makes use of novel filtering techniques. Numerical examples of arrays of microstrip patches and dielectric resonator antennas covering a wide variety of requirements on these parameters are presented.

Full-wave analysis of the GALILEO System Navigation Antenna by means of the generalized scattering matrix of a finite array

A full-wave methodology has been used to analyse the GALILEO system navigation antenna for the space segment of the global positioning system. It is a multilayer array structure composed by cavity-backed microstrip patches in stacked configuration, and coaxial probe feeding. It follows a hexagonal regular lattice that makes possible to perform a modular analysis in two steps. First, each isolated array element is modeled considering a finite hexagonal metallic flange. A generalized scattering matrix (GSM) of each element is obtained in terms of coax and spherical modal expansions from a hybrid 3-D finite elements-modal analysis method (SFELP). Next, the GSMs of the array elements are analytically connected by using properties of rotation and translation of spherical modes to obtain the overall GSM of the array. This matrix provides the impedance, coupling and radiating characteristics of the array on a finite ground plane. Radiation patterns of the isolated element and the array have been obtained and compared with measurements.

Antenna Modeling by Elementary Sources Based on Spherical Waves Translation and Evolutionary Computation

A method based on spherical waves translation and evolutionary computation is used to model antennas efficiently. A set of infinitesimal dipoles is taken into account instead of the antenna, optimizing the number and positions of the dipoles by using a binary genetic algorithm (GA) for modeling the near field with a desired accuracy. It is shown how this approach can model volumetric antennas by a set of equivalent sources placed on a ground plane accurately. Moreover, large finite arrays can be quickly simulated since GA is only applied to analyze an isolated element, avoiding the need of distributing equivalent sources regularly over an equivalent surface.