J. A. Rodríguez-González

Genetic algorithms in the design and optimization of antenna array patterns

This paper demonstrates the application of genetic algorithms (GAs) in array pattern synthesis. GAs have the ability to escape from local minima and maxima and are ideally suited for problems where the number of variables is very high. We present three examples: two for linear arrays and one involving linear and planar arrays.

Rapid Method for Finding Faulty Elements in Antenna Arrays Using Far Field Pattern Samples

A simple and fast technique that allows a diagnosis of faulty elements in antenna arrays, that only needs to consider a small number of samples of its degraded far-field pattern is described. The method tabulates patterns radiated by the array with 1 faulty element only. Then, the pattern corresponding to the configuration of failed/unfailed elements under test is calculated using the error-free pattern and the patterns with 1 faulty element. The configuration with the lowest difference between the calculated and the degraded patterns is selected. Comparison of the performance of this method using an exhaustive search and a genetic algorithm for an equispaced linear array of 100 lambda/2-dipoles is shown. Mutual coupling as well as noise/measurement errors in the pattern samples were considered in the numerical analysis.

Fast Array Thinning using Global Optimization Methods

A simple and fast method to accelerate the global optimization approaches used in array thinning is described. This method tabulates the contribution of every array element to the far-field pattern in order to improve the numerical efficiency of the optimization algorithm employed. Experiments using our proposal alongside with a genetic algorithm reduce the search computation time about 90%.

Synthesis of Very Large Planar Arrays for Prescribed Footprint Illumination

Footprint patterns can be efficiently synthesized by means of planar arrays with hundreds or thousands of elements: an efficient combination of Woodward-Lawson and Orchard-Elliott-Stern roots optimization procedure is suggested. This hybrid technique is applied to a footprint covering Europe by using planar arrays with isotropic elements and linearly polarized circular patches. The proposed method keeps under control both the side lobe and ripple level of the synthesized pattern.

Electromagnetic fields at 2.45 GHz trigger changes in heat shock proteins 90 and 70 without altering apoptotic activity in rat thyroid gland

Summary Non-ionizing radiation at 2.45 GHz may modify the expression of genes that codify heat shock proteins (HSP) in the thyroid gland. Using the enzyme-linked immunosorbent assay (ELISA) technique, we studied levels of HSP-90 and HSP-70. We also used hematoxilin eosin to look for evidence of lesions in the gland and applied the DAPI technique of fluorescence to search for evidence of chromatin condensation and nuclear fragmentation in the thyroid cells of adult female Sprague-Dawley rats. Fifty-four rats were individually exposed for 30 min to 2.45 GHz radiation in a Gigahertz transverse electromagnetic (GTEM) cell at different levels of non-thermal specific absorption rate (SAR), which was calculated using the finite difference time domain (FDTD) technique. Ninety minutes after radiation, HSP-90 and HSP-70 had decreased significantly (P<0.01) after applying a SAR of 0.046±1.10 W/Kg or 0.104±5.10−3 W/Kg. Twenty-four hours after radiation, HSP-90 had partially recovered and HSP-70 had recovered completely. There were few indications of lesions in the glandular structure and signs of apoptosis were negative in all radiated animals. The results suggest that acute sub-thermal radiation at 2.45 GHz may alter levels of cellular stress in rat thyroid gland without initially altering their anti-apoptotic capacity.

Low-Sidelobe Patterns From Small, Low-Loss Uniformly Fed Linear Arrays Illuminating Parasitic Dipoles

Low-sidelobe radiation patterns with good directivity can be generated by antennas consisting of a linear array of parasitic dipoles in front of a smaller linear array of active dipoles fed uniform voltages, a configuration that facilitates the task of feed network design. The fundamental effect of the parasitic array is to allow the length of the active array to increase by a factor of 2 or more, thereby narrowing beamwidth while the parasitic elements keep side lobes low to ensure good directivity. For a given number of active elements, performance improves as the number of parasitic dipoles increases, levelling off when there are about twice as many parasitic as active elements. The method is easily generalizable to planar arrays.

Synthesis of Taylor-Like Patterns With Uniformly Excited Multi-Ring Planar Antennas

In this paper, we describe the synthesis of circular-Taylor-like patterns for antennas composed of concentric rings of uniformly excited elements. Optimization of the ring radii achieves close approximation to the envelope of the desired pattern within a given cone about the main beam. An alternative approach, using annular subarrays, speeds computations by limiting the number of between-ring spacings. Examples illustrate the potential of these methods.

Synthesis of Array Radiation Pattern Footprints Using Radial Stretching, Fourier Analysis, and Hankel Transformation

For the synthesis of radiation patterns using antenna arrays with thousands of elements, the combination of direct methods with non-stochastic optimization can be more efficient than stochastic optimization. Here we describe an efficient method for the synthesis of footprint patterns that combines Hankel transformation with Fourier analysis following angle-dependent homothesis (i.e., radial stretching and/or shrinking) of an axisymmetric Elliott-Stern pattern for a circular aperture. The new method can in principle be applied to arrays of radiating elements with arbitrary locations and element patterns.

Design of Planar Arrays Composed by an Active Dipole Above a Ground Plane with Parasitic Elements

In this paper, several simple antenna designs based on the use of an active dipole placed above a ground plane with an array of parasitic dipoles are presented. The parasitic dipoles are used to modify the pattern of the active dipole yielding a pencil beam of moderate gain. The use of one active element provides a very simple feeding network that reduces the complexity of the antenna. The proposed technique optimizes the geometry and conflguration of both active and parasitic elements. It is shown that the performance of the designed antennas is considerably better than that of a similar antenna without parasitic elements.

Experimental Results on a Planar Array of Parasitic Dipoles Fed by One Active Element

A planar array composed of 41 parasitic dipoles above a ground plane, fed by an active dipole at 5 GHz was designed to obtain a pencil beam pattern with a moderate gain and bandwidth. Experimental results are in good agreement with the theory and show a pattern with an 18.78 dB gain, a sidelobe level (SLL) of −15 dB, an impedance bandwidth of 16.53% (the frequency range over which the value of S11 is below −10 dB) and a 2.7% bandwidth that is achieved within 1dB gain variations.