Antenne Triplaque Omnidirectionnelle

Le développement de la technologie Ultra Large Bande (ULB) doit s'accompagner de la mise au point de nouvelles antennes capables de fonctionner classiquement sur la plage de fréquence 3.1 – 10.6 GHz tout en présentant un comportement temporel adéquat à la transmission de pulses courts. Une structure proposée ici est l'antenne large fente triplaque possédant une alimentation en forme de fourche, étudiée avec et sans plan de masse. Cette dernière offre une adaptation de 123 % avec une bonne stabilité de rayonnement (bi-directionnalité dans le plan E et omni-directionnalité dans le plan H). L'utilisation de diagrammes de rayonnement 2D en amplitude et en phase en fonction de la fréquence ainsi que l'analyse du pulse émis par cette structure permettent de mettre en évidence ses caractéristiques de rayonnement temporel. L'antenne triplaque est capable de transmettre une impulsion brève sans apporter de distorsion

Enhancement of the quadrupole interaction of an atom with guided light of an ultrathin optical fiber

We investigate the electric quadrupole interaction of an alkali-metal atom with guided light in the fundamental and higher-order modes of a vacuum-clad ultrathin optical fiber. We calculate the quadrupole Rabi frequency, the quadrupole oscillator strength, and their enhancement factors. In the example of a rubidium-87 atom, we study the dependencies of the quadrupole Rabi frequency on the quantum numbers of the transition, the mode type, the phase circulation direction, the propagation direction, the orientation of the quantization axis, the position of the atom, and the fiber radius. We find that the root-mean-square (rms) quadrupole Rabi frequency reduces quickly but the quadrupole oscillator strength varies slowly with increasing radial distance. We show that the enhancement factors of the rms Rabi frequency and the oscillator strength do not depend on any characteristics of the internal atomic states except for the atomic transition frequency. The enhancement factor of the oscillator strength can be significant even when the atom is far away from the fiber. We show that, in the case where the atom is positioned on the fiber surface, the oscillator strength for the quasicircularly polarized fundamental mode HE$_{11}$ has a local minimum at the fiber radius $a\simeq 107$ nm, and is larger than that for quasicircularly polarized higher-order hybrid modes, TE modes, and TM modes in the region $a<498.2$ nm

Frequency tunable antenna for digital video broadcasting handheld application

International audienceIn this paper, we present a frequency tunable antenna suitable for Digital Video Broadcasting Handheld applications. Due to the narrow operating frequency band of the antenna derived from a monopole coupled loop antenna, a tuning system has been proposed to sweep the narrow band on a large frequency range in order to cover the DVB-H frequency bandwidth [470-702] MHz. We provide results of this antenna mounted on a circuit board simulating a terminal handset