Current Issue : January - March Volume : 2013 Issue Number : 1 Articles : 6 Articles
A single varactor-tuned element is investigated as effective solution for the realization of reconfigurable reflectarray antennas. The\r\nproposed configuration is successfully implemented for the design of an X-band reflectarray prototype of 3 Ã?â?? 15 radiators. A\r\ndedicated electronic control board is designed as an integral part of the antenna. Good performances in terms of beam-scanning\r\ncapabilities are obtained from measurements....
A reverberation chamber is a convenient tool for over-the-air testing of MIMO devices in isotropic environments. Isotropy is\r\ntypically achieved in the chamber through the use of a mode stirrer and a turntable on which the device under test (DUT) rides.\r\nThe quality of the isotropic environment depends on the number of plane waves produced by the chamber and on their spatial\r\ndistribution. This paper investigates how the required sampling rate for the DUT pattern is related to the plane-wave density\r\nthreshold in the isotropic environment required to accurately compute antenna correlations. Once the plane-wave density is above\r\nthe threshold, the antenna correlation obtained through isotropic experiments agrees with the antenna correlation obtained from\r\nthe classical definition, as has been proven theoretically. This fact is verified for the good, nominal, and bad reference antennas\r\nproduced by CTIA. MIMO channel capacity simulations are performed with a standard base station model and the DUT placed\r\nin a single-tap plane-wave reverberation chamber model. The capacity curves obtained with the good, nominal, and bad reference\r\nantennas are clearly distinguishable....
A novel high-gain textile antenna array system, fully integrated into a rescue-workerââ?¬â?¢s vest and operating in the Industrial,\r\nScientific, and Medical wireless band (2.4ââ?¬â??2.4835 GHz), is presented. The system comprises an array consisting of four tiptruncated\r\nequilateral triangular microstrip patch antennas (ETMPAs), a power divider, line stretchers, and coaxial cables. The array\r\nis vertically positioned on the human torso to produce a narrow beam in elevation, as such reducing fading and allowing to steer\r\nthe maximum gain in a small angular sector centered around the broadside direction. To allow simple low-cost beam steering, we\r\nspecifically minimize mutual coupling by using a relative large distance between the patches and by selecting the ETMPA element\r\nas the most suited topology from three potential patch geometries.Moreover, we investigate the stability of return loss and mutual\r\ncoupling characteristics under different relative humidity conditions, when bending the array, when placing the system on-body,\r\nand when covering it by different textile layers. Reflection coefficient and gain patterns are simulated and measured for the antenna\r\nsystem in free space and placed on the human body....
Lightning electromagnetic field is obtained by using ââ?¬Å?engineeringââ?¬Â models of lightning return strokes and new channel-base\r\ncurrent functions and the results are presented in this paper. Experimentally measured channel-base currents are approximated\r\nnot only with functions having two-peaked waveshapes but also with the one-peaked function so as usually used in the literature.\r\nThese functions are simple to be applied in any ââ?¬Å?engineeringââ?¬Â or electromagnetic model as well. For the three ââ?¬Å?engineeringââ?¬Â models:\r\ntransmission line model (without the peak current decay), transmission line model with linear decay, and transmission line model\r\nwith exponential decay with height, the comparison of electric and magnetic field components at different distances from the\r\nlightning channel-base is presented in the case of a perfectly conducting ground. Different heights of lightning channels are also\r\nconsidered. These results enable analysis of advantages/shortages of the used return stroke models according to the electromagnetic\r\nfield features to be achieved, as obtained by measurements....
This paper presents a formulation for shaping the main reflector of an axis-symmetric dual-reflector antenna designed to offer\r\nan omnidirectional coverage with an arbitrary radiation pattern in the vertical plane. The subreflector is generated by an axisdisplaced\r\nconic, and the main reflector is shaped to achieve a prescribed far-field radiation pattern. The procedure is based on\r\ngeometrical optics (GO) principles. Two distinct far-field ray structures are explored and their limitations are identified. The GO\r\nshaping results are validated by analysis provided by the accurate method of moments technique....
The vision and ideas of wearable computing systems describe future electronic systems as an integral part of our everyday\r\nclothing that provides the wearer with such intelligent personal assistants. Recently, there has been growing interest in the antenna\r\ncommunity to merge between wearable systems technology, ultrawideband (UWB) technology and textile technology. This work\r\naimed to make closer steps towards real wearability by investigating the possibilities of designing wearable UWB antenna where\r\ntextile materials are used for the substrate as well as the conducting parts of the designed antenna. Two types of conducting\r\nmaterials have been used for conducting parts, while a nonconducting fabric has been used as antenna substrate material. A set\r\nof comparative results of the proposed design were presented and discussed. Moreover, effects on the return loss by means of\r\nmeasurements for each fabricated antenna prototype under bent and fully wet conditions were discussed in more details....
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