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.

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The aim of this work is to get far field radiation patterns for any radiating source from transient acquisition, in a large frequency range. An outdoor transient Ultra-Wideband near-field measurement base will be installed, a single time pulse radiated by the source will cover the desired spectrum, and the accurate determination of far field radiations will be accomplished by means of cylindrical waves' modal development. This method uses simplified test equipments, easy to be installed, and it reduces measurement costs.

Abstract-An ultra wideband radar system based on a coherent emission of an ultra-wideband antenna array using photoconductive switching devices is proposed. The triggering process is obtained by the excitation of semiconductor samples in linear mode using a picosecond laser source. The emitting antenna system and the receiving antenna developed by the Research Institute XLIM present some specific qualities suitable for radiation and measurement of ultrashort pulses. The optical control of the sources allows to sum the The experiments realized with this optoelectronic array validate these two concepts. Another way of improving these systems is proposed. It involves using bipolar pulse generators.

We propose a novel ultrawideband (UWB) antenna designed specially for transient UWB radar applications. This work is a part of a new project concerning an optoelectronic UWB radar demonstrator with an array of four antennas. This project required the development of a new UWB antenna: the Valentine antenna. This antenna must be lighter and more compact in H-plane to allow the assembly of the array. This array must have a volume lower than 1 m . This antenna, which is composed of curved metallic strips, radiates ultrashort pulses in the frequency band 300 MHz -3 GHz with very low dispersion, a high gain and a low cross-polarization in the axial direction. The Valentine antenna must support 10 kV of peak voltage. This paper describes the Valentine antenna and its main radiation characteristics.

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