A novel ultrawideband (UWB) antenna, called the Shark antenna, and designed especially for transient applications is proposed in this paper. A Shark antenna array is also conceived in order to obtain a high power UWB pulse radiation source through the frequency band [800 MHz-8 GHz]. For this application, the elementary antenna must be compact, non-dispersive, and the array must have a high transient front to back ratio. The geometry of the Shark antenna and its radiation characteristics are detailed. Moreover, an approach which evaluates the transient front to back ratio of a square array is presented. Index Terms-High power radiations, miniature ultrawideband (UWB) antenna, transient array.
The conception of a novel Ultra-Wideband (UWB) antenna array, designed especially for transient radar applications through the frequency band (300 MHz–3 GHz), is proposed in this paper. For these applications, the elementary antenna must be compact and nondispersive, and the array must be able to steer in two dimensions. The geometry of the elementary antenna and its radiation characteristics are presented. The array beam steering is analyzed and a technique making the increase of the transient front-to-back ratio possible is described.
Today’s techniques to recover heavy oil are mining, when possible, or steam injection. For steam injection, once the oil is heated, its viscosity is reduced; it becomes mobile and can be extracted. In some cases, when steam injection isn’t efficient, other methods should be developed, one of them is based on electrical technology. One solution studied by Total to reduce viscosity when steam injection isn’t possible or efficient, is to use Radio Frequency heating. The electromagnetic waves have the capability to heat immediately deeper than steam. To improve efficiency of this process, we developed a downhole Radio Frequency generator composed of triodes. An antenna is added to form a complete assembly. Here, we will present the advantages of this original solution patented by Total. The optimization of this device concerns the impedance adaptation between generator and the antenna. But the impedance of this antenna depends also on the electrical characteristics of the reservoir. The reservoir’s impedance is mainly determined by the water in liquid phase. One critical parameter is the complex electric permittivity. This parameter impacts directly on the conversion from the electrical energy to heat, the dissipated power in the reservoir being related to the complex part of the permittivity. In this paper, we will show a solution to keep an optimum conversion ratio from high frequency electrical energy to heat. As the impedance varies with time and reservoir heating, the optimum radiating frequency of our system has to vary too. The choice of the central frequency could also depend on the presence of iron oxide in shale layer in the hydrocarbon reservoir. In this paper, we will choose a frequency around 10 MHz and we will show different spatial repartitions of the applied electrical field and the corresponding heated zone. The frequency band is a compromise between fast heating and depth of penetration: the lower the frequency, the deeper the electromagnetic waves penetrate in the reservoir.
Y. Jacques : directeur de recherche au Cnrs. 1. Anegon : chargé de recherche à l'Inserm. M. M. Hallet : maître de conférence des universités. A. Godard : maître de conférence des universités, praticien hospitalier. J.-P. Moisan : maître de conférence des universités, praticien hospitalier. J. P. Soulillou : professeur d'immunologie, directeur de l'U.211 de l'Inserm. Inserm U.211, insti tut de biologie, 9, quai Moncousu,
This paper deals with miniaturization techniques and radiating optimization on UWB antenna in order to make an antenna array. The hard point with size reduction of an antenna is the back radiation, the cross polarization and the antenna adaptation. Several methods to keep the antenna adapted to our bandwidth [300MHz -3GHz] are studied. A detailed study of the travelling wave elementary antenna is proposed. Some techniques are applied to reduce back radiation and cross polarization by the use of slots in order to reduce back radiation and resistive loads in order to reduce surface current levels and side cross polarization.
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