N.J. McEwan

Wideband Printed MIMO/Diversity Monopole Antenna for WiFi/WiMAX Applications

A novel printed diversity monopole antenna is presented for WiFi/WiMAX applications. The antenna comprises two crescent shaped radiators placed symmetrically with respect to a defected ground plane and a neutralization lines is connected between them to achieve good impedance matching and low mutual coupling. Theoretical and experimental characteristics are illustrated for this antenna, which achieves an impedance bandwidth of 54.5% (over 2.4-4.2 GHz), with a reflection coefficient <;-10 dB and mutual coupling <;-17 dB. An acceptable agreement is obtained for the computed and measured gain, radiation patterns, envelope correlation coefficient, and channel capacity loss. These characteristics demonstrate that the proposed antenna is an attractive candidate for multiple-input multiple-output portable or mobile devices.

A new design of horizontally polarizedand dual-polarized uniplanar conical beam antennas for HIPERLAN

It is shown that a conical beam 5.2-GHz antenna suitable for HIPERLAN application, but working in horizontal polarization, can be realized as a group of microstrip patch radiators in a ring formation. Layouts with three and four patches are described, and radiation patterns are found to agree well with predictions from a simple array model. The three-patch form is smaller and gives a closer approximation to an azimuth-independent pattern. Patterns are very similar to those achieved in vertical polarization with previously reported disk antenna realizations, giving peak radiation at about 50/spl deg/ elevation. Two methods of impedance matching are found to give satisfactory results. A dual-polarized conical-beam microstrip antenna, with a strictly uniplanar conductor pattern, is also presented and realized as an array of three square patches whose corners meet a central feed point. For the second polarization, the antenna functions as a series fed array. Fairly good conical beam patterns have been obtained, though only moderate polarization purity appears to be obtainable from three-element arrays.

A Low-Profile Ultra-Wideband Modified Planar Inverted-F Antenna

A miniaturized modified planar inverted-F antenna (PIFA) is presented and experimentally studied. This antenna consists of a planar rectangular monopole top-loaded with a rectangular patch attached to two rectangular plates, one shorted to the ground and the other suspended, both placed at the optimum distance on each side of the planar monopole. The fabricated antenna prototype had a measured impedance bandwidth of 125%, covering 3 to 13 GHz for reflection coefficient better than -10 dB. The radiator size was 20×10×7.5 mm3, making it electrically small over most of the band and suitable for incorporation in mobile devices. The radiation patterns and gains of this antenna have been cross-validated numerically and experimentally and confirm that this antenna has adequate characteristics for short range ultra-wideband wireless applications.

Compact WLAN disc antennas

A novel conical beam patch antenna design, suitable for local area network applications, uses a central cylindrical connection from the disc to ground to achieve a large reduction in resonant size. Results on efficiency, bandwidth, and pattern are reported for several prototypes.

An approach for calculating the limiting bandwidth- reflection coefficient product for microstrip patch antennas

The bandwidth of a microstrip patch antenna is expressed in terms of minimum achievable reflection coefficient using an equivalent circuit and the Bode-Fano theory. The bandwidth-reflection coefficient product is found to be proportional to antenna height and largely independent of feed probe position, for small bandwidths. The product can be computed directly from a numerical evaluation of the first-order Bode-Fano integral. Curves are presented showing how the product becomes limited by the feed probe inductance at very large bandwidths. It is concluded that this effect is unlikely to be a limit on the potential bandwidth of a practical patch antenna. If as a minimal correction the feed inductance is tuned out, the realized bandwidth with low order matching or optimal over-coupling shows the expected relationship to the theoretical limit.

A power and efficiency measurement technique for active patch antennas

In this paper, the power input to the radiating element of an active microstrip patch antenna is measured using a small sensing patch, which is weakly coupled to a radiating edge. Combined with an estimate of patch radiation efficiency, this also yields a measurement of total radiated power. The method has advantages of convenience, insensitivity to room reflections, and a weakly frequency-dependent calibration factor.

Design and analysis of UC-EBG on mutual coupling reduction

A new Uniplanar Compact Electromagnetic Bandgap (UC-EBG) structure is proposed in order to achieve a smaller unit cell operating at lower frequency stop band. Its design is detailed and an experimental result is presented. The property of the proposed UC-EBG is compared with the distorted uniplanar compact EBG (DUC-EBG). The application of the proposed UC-EBG is examined. A parametric study on various thicknesses of dielectric substrate is also discussed.

OTS propagation measurements during thunderstorms

Otspropagation measurements are described which comprise a complete determination of the incoming polarizations for both linearly and circularly polarized beacons. Auxiliary equipment includes radars, E-field sensors and a microphone array. General trends in the propagation data are discussed and two basic models are proposed for the observed correlations between electrostatic field and cross-polarization. A detailed analysis, with radar data, is now given for one thunderstorm. A method for the prediction of the linear cross-polarization from the circular is shown to work well for this ice-dominated event. Fast lightning-induced, cross-polar jumps are described, and by relating them to acoustic thunder location data, the physical models for particle alignment are discussed.AnalyseOn décrit des mesures de propagation avec le satelliteOtscomprenant la détermination complète des polarisations reçues, pour les balises à polarisation rectiligne ou circulaire. L’équipement auxiliaire comprend deux radars, deux capteurs de champ électrique et un réseau de microphones. On analyse les caractéristiques générales de la propagation, en présentant deux modèles pour des corrélations entre le champ électrostatique et la transpolarisation. Un orage est analysé en détail à partir des données des radars. Une méthode de prévision de la transpolarisation en polarisation rectiligne à partir de celle observée en polarisation circulaire convient bien à ce phénomène dominé par des particules de glace. Des sauts rapides entre polarisations croisées sont provoqués par les éclairs. En les identifiant parmi les données de localisation acoustique, on discute des modèles physiques d’alignement des particules.

A modified radiometric method for measuring antenna radiation efficiency

Radiation efficiency of antennas is shown to be measurable by a modified radiometric technique where the antennas physical temperature is varied, rather than the noise temperature of its surroundings. The method is accurate, flexible and much more convenient for routine use. A means of avoiding errors caused by temperature-dependent antenna impedance is described. The accuracy of the method is verified by measuring the radiation efficiency of a horn antenna with a 3 dB attenuator to simulate a 50% efficient antenna, and by using microstrip patch antennas, whose measured efficiencies compared well with values computed from a transmission-line model.

Efficient autonomous heliostat system

In this work, an efficient autonomous solar energy system has been implemented for domestic use. It concentrates the solar heat to turn water into steam which in turn is channelled to drive an electricity turbine-generator. The prototype utilizes two heliostat reflector units, each of which has been designed to accurately and independently track the sun throughout the day and reflect its light constantly on a water tank through a Fresnel lens. The algorithm is flexible enough to accept up to 100 units and can accommodate the four seasons of the year. The performance of the system including the instantaneous generated power can be monitored wirelessly using a specially designed Computer User Interface. The final system produced a concentration efficiency of 86%-92%.