Network Methods Applied to Multilayered Cylindrical Radiating Structures

Abstract

This work deals with the development of methods, algorithms and software implementations, for the analysis, design and optimization of multilayered radiating cylindrical structures.A method based on the integral equation method (IEM) in connection with method of moment (MOM) is developed. Dealing with IEM a key problem is the computation of the Green's function.A novel method to compute the Green's function for multilayered cylindrical structures is presented. Making use of the symmetry properties of the cylindrical structure a circuit description of multilayered cylindrical structure in spectral domain (SD) is developed. The circuit model is based on generalized transmission lines (GTL). The GTL method is used to compute the spectral domain dyadic Green's function components. The space domain Green's functions are computed using a quasi-analytical approach. This means that we approximate the spectral domain Green's functions using a poles/residues expansion into a series of exponential functions. The poles and residues are estimated using the generalized pencil of function (GPOF) method. Having the spectral domain components of the dyadic Green's function represented by exponential functions, the space domain Green's function is performed analytically.The convergence of the cylindrical Green's function near the source region are treated in details. For this purpose we consider that the Green's function is given in terms a series of cylindrical waves functions. Due to the singularity of the Green's function in the origin, the correct and fast convergence in the near field is an important issue. In this work we present a convergence analysis of the cylindrical Green's function. In this context the availability of simple and accurate reference models for the evaluation of the method in the near field region is a key point. From the analytical point of view, the problem is solved by the theory of distribution. In this iii iv Table of Contents work, we discuss the limitations of the classical description of the source region given by the theory of distribution from the numerical implementation point of view.In order to show the potentialities and to validate the method, we present several challenge applications. The Green's function is used with MOM for the modelling of conformal cylindrical antennas embedded in a cylindrical radome structure and circular conformal antenna array mounded around a cylindrical mast acting as reflector. In order to demonstrate one important advantage rotational symmetric structures, we present beamforming and azimuthal scanning algorithms combined with electromagnetic simulations of the antenna array without and with a three layers radome. Although beam-shaping has advanced properties, the proposed method for numerical modelling is rather fast and efficient. Indeed, due to the fast semianalytical approach presented in this work, we show that the computation can be carried out quasi simultaneously. The results are compared with measurements and with results obtained with others c...