J.C. Bregains

Signal Radiation and Power Losses of Time-Modulated Arrays

We review and formalize the mathematical background of time-modulated linear arrays (TMLAs); then, a number of issues are examined. First, for signal transmission applications, restrictions to the frequencies involved in the procedure are highlighted. Second, the sideband power losses associated to the technique are thoroughly examined, introducing a coefficient appropriate to evaluate the efficiency of the procedure. Finally, a closed form expression for the total power associated to sideband radiation is obtained, very convenient for the implementation of real-time optimization of the system. Relevance of additional research on the subject is highlighted.

Element failure detection in linear antenna arrays using case-based reasoning

The present work proposes a novel case-based reasoning system for fault diagnosis in moderate or large linear antenna arrays. This system identifies the set of elements that are most likely to be defective, helping to significantly reduce the computational costs of their detection (e.g., using an optimization technique such as a genetic algorithm).

New Toroidal Beam Antennas for WLAN Communications

The design of a number of new antennas that radiate linearly polarized toroidal beams is described. The developed procedures are based on the use of a method of moments commercial software tool. Several numerical examples, working at WLAN communication frequencies, are derived and analyzed. Two experimental prototypes validate the numerical results

Avoiding interference in planar arrays through the use of artificial neural networks

This article implements an artificial neural network to find, through computer simulation, the excitations of a square planar array. The array is composed of 52 uniformly spaced subarrays, and has a quasi-null in its radiation diagram. This simulation model includes the reduction of any signal interference in the shaped radiating zone after its position has been determined.

Analytical and optimization methods for linear arrays with high efficiency and low sidelobes

Array distributions that have a uniformly excited central segment and a monotonically decreasing outer segment have been shown to yield low sidelobe patterns with specified constraints on the effective radiated voltage (ERV). An analytical method has been previously presented for generating these distributions using a constrained least squares (CLS) method, given constraints on both the peak amplitude of the elements and the ERV. Simulated annealing (SA) is a versatile global optimization technique that has been effectively used for a wide variety of array applications. In this paper, we compare the results obtained from generating radiation patterns for linear arrays with high aperture efficiency and low sidelobes using the CLS method and SA optimization.

Visualizing the 3D polar power patterns and excitations of planar arrays with Matlab

This paper discusses the use of Matlab to create three-dimensional polar plots of the power patterns of planar arrays together with 3D plots of the amplitudes and phases of their excitations. A few lines of Matlab M-code suffice to create complex plots.

Optimal Synthesis Of Circular Apertures Based On Ludwig Distributions

Ludwig distributions are a generalization of circular Taylor distributions that generate radiation patterns with wide-angle side lobe levels decaying faster than for Taylor patterns. In this paper we show that by means of an appropriate optimization technique the zeros of Ludwig patterns can be perturbed so as to improve or modify pattern and/or aperture distribution characteristics without altering the wide-angle decay behavior. The examples presented include footprint patterns, pencil beam patterns with individually controlled side lobe heights, footprint beams generated by real excitations, and pencil beam patterns with aperture distributions that are smoother than the original Ludwig distribution.

Effects of measurement distance on measurements of symmetrically shaped patterns generated by line sources

Symmetrically shaped patterns, generated by real continuous linear apertures derived from Taylor distributions, resemble Taylor sum patterns in regard to the distance-dependence of their sidelobe heights. Their ripple shows negligible near-field degradation. If the aperture distribution is complex, however, the ripple and sidelobe levels show previously unreported degradation behavior, including a lowering of the first sidelobe level.

A first insight into the analysis of signal transmission and power losses in time-modulated linear arrays

In this paper it was demonstrated that signal transmission is possible with time-modulated arrays. In a second analysis, the power loss was explicitly written out, giving this to the designer the possibility of obtaining a precise calculation of its amount. The restrictions that must be imposed on the angular frequencies that are involved in the process, i.e., the carrier frequency, the time-pulse frequency and the (narrowband) signal frequency, should be also considered. Due to lack of available space, this was not done in this paper. Further details about this subject will be discussed during the presentation of this work in the Symposium

Almost uniformly excited arrays

Antenna arrays with good performance that are uniformly excited except for the amplitudes and/or phases of a small minority of elements can be synthesized using genetic algorithms. We consider only the achievement of low side lobe levels by symmetric linear and quadrantally symmetric square planar arrays in which either the phase or the amplitude of the excitation is uniform; although it must always be borne in mind that there is a trade-off between the demands put on the pattern and the simplicity of the aperture distribution, we note that in principle the same approach, possibly with alteration of both phase and amplitude, can be used to synthesize arrays generating more complex patterns.