Stefano Selleri

Differentiated Meta-PSO Methods for Array Optimization

The particle swarm optimization (PSO) method has been successfully applied to different electromagnetic optimization problems. Because of the complexity of this kind of problems, the associated cost function is in general computationally expensive. A fast convergence of the optimization algorithm is hence required to attain results in short time. Here few variations over the standard algorithm, referred to as differentiated meta-PSO, aimed to enhance the global search capability, and to improve the algorithm convergence, are introduced. In order to verify their effectiveness the different techniques have been first applied to benchmark test functions and then used for the optimization of a planar array.

Some Insight Over New Variations of the Particle Swarm Optimization Method

The Particle Swarm Optimization (PSO) method recently gained high popularity in electromagnetics. Here few variations over the standard algorithm, referred to as Meta PSO, are proposed and the results of their application to the optimization of a microwave microstrip-line filter are presented.

Genetic Algorithm Optimization of High-Efficiency Wide-Band Multimodal Square Horns for Discrete Lenses

By properly exciting higher order modes at an aperture it is possible to achieve higher aperture efficiencies. High efficiency antennas are mandatory in many applications, as discrete lenses, since the single element efficiency deeply affects the efficiency of the whole lens. In this contribution a genetic algorithm is applied to the mode matching analysis of square horns to achieve high radiation efficiency over a relatively wide band.

Characterization of dielectric materials with the finite-element method

A technique to characterize homogeneous and inhomogeneous dielectric materials based on measurements and computations is presented. The first step of the method proposed consists of measuring the resonant frequencies of an arbitrarily shaped cavity containing an arbitrarily shaped sample of the material under test. In the second step, the measured data are used in two different algorithms, both based on the finite-element method, to solve for the dielectric constant.

PHASE CENTRE OPTIMIZATION IN PROFILED CORRUGATED CIRCULAR HORNS WITH PARALLEL GENETIC ALGORITHMS

Achieving a high stability of the phase centre position in horn antennas with respect to frequency is a very desirable aim in reflector antenna design; a highly stable phase centre reduces efficiency dropping for defocusing at the frequency band extremes. By using an appropriate profile for the horn antenna it is possible to obtain horns both compact and with a stable phase centre. In this paper an automatic design procedure, based on Genetic Algorithms, to obtain such horns is described. The algorithm operates on many horn profile parameters, including corrugations, and is based on an accurate fullwave mode matching/combined field integral equation analysis code. To keep computing time down a full parallel algorithm over a 12 CPU parallel virtual machine is described.

Passive intermodulation on large reflector antennas

In this work, an analytical model for the study of passive intermodulation (PIM) on large reflector antennas is presented. Passive intermodulation, in the scattered field, arises when the scatterer is nonlinear, or when it presents junctions connecting linear materials. Its presence causes a degradation of some antenna parameters and, especially, the cross-polar level, which may rise by several tens of dB. It would then be useful to develop a technique to predict its influence, in order to take appropriate steps during antenna design. A heuristic model for the junction problem has previously been derived and validated with measurements in a time-domain physical optics (TD-PO) framework. These results are applied here to a TD-PO analysis of reflector antennas, in particular, for a satellite-communication antenna and for a radio-astronomy antenna.

Profiled corrugated circular horns analysis and synthesis via an artificial neural network

In many reflector and lens antennas profiled corrugated circular horns constitute one of the best feed solution thanks to their polarization purity and small size. In this paper, a method for the design of these feeds by using an artificial neural network (ANN) approach is described. The results obtained with such an approach are investigated both for the analysis and for the synthesis problem, and compared with the standard methods. This unconventional solution gives a good level of accuracy and shorter processing times especially for the synthesis problem, where there is still a lack of affordable and fully automated procedures.

Improved PSO algorithms for electromagnetic optimization

Some variations over the basic particle swarm algorithm are here proposed, aimed at a more efficient search over the solution space and exhibiting a negligible overhead in complexity and speed. The proposed algorithms are then applied to the test case of a microwave filter to show their superior capabilities with respect to the conventional algorithm.

A hybrid finite-element-modal-expansion method with a new type of curvilinear mapping for the analysis of microwave passive devices

A hybrid finite-element-modal-expansion procedure for the three-dimensional analysis of passive microwave devices exploiting higher order vector basis functions and an innovative class of curved elements is presented. If modal expansions on ports are not analytically known, they can be numerically obtained via a preliminary two-and-one-half-dimensional finite-element analysis; curved triangular and tetrahedrical elements are defined by a rational Bezier mapping, which provides a remarkable increase in accuracy and flexibility over the conventional polynomial mapping without a significant increase in computational burden. Numerical results are provided to illustrate the efficiency and feasibility of the proposed technique.

Numerical analysis of the diffraction at an anisotropic impedance wedge

A numerical approach to the electromagnetic scattering of a plane wave impinging at skew incidence on the edge of a wedge with two different anisotropic face impedances is presented. The diffracted field is obtained by applying the finite-difference (FD) method to solve two coupled parabolic equations. The solution obtained is valid in the high-frequency region.