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In this paper we exhibit a novel approach to the problems of topic and speaker identification that makes use of a large vocabulary continuous speech recognizer. We present a theoretical framework which formulates the two tasks as complementary problems, and describe the symmetric way in which we have implemented their solution. Results of trials of the message identification systems using the Switchboard corpus of telephone conversations are reported.

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International audienceWe describe here an optimization procedure to shape the radiation pattern of planar two-dimensional (2-D) leaky-wave antennas. The structures under investigation are superstrate configurations made by partially reflecting screens (impedances sheets) over a ground plane and excited by open-ended waveguides. The antenna configuration providing the required radiation pattern is obtained by resorting to an ad hoc optimization procedure that minimizes the mean squared error between the target pattern and the actual radiated far field. The radiated field is analytically evaluated using a Green's function spectral approach to speed up the optimization process. Several kinds of radiation patterns can be obtained using the proposed algorithm. In this work, we focus our attention on flat-topped radiation patterns, suitable as element pattern for phased array antennas covering a limited angular field of view such as those considered for space applications. The proposed procedure is validated by full-wave results and measurements

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International audienceWe proposed a synthesis method to design thinned leaky-wave-based arrays. The array elements are small waveguide apertures opened on a ground plane. A superstrate (impedance sheet, dielectric slab, etc.) is placed above the array. The array elements excite leaky-wave modes between the ground plane and the superstrate, enhancing the aperture efficiency of the final antenna. An iterative optimization procedure based on a convex l1 minimization is used to reduce the number of array elements, maintaining the radiated field within a predefined mask. All the embedded element patterns are evaluated for each source through a fast Green's function spectral approach, taking into account the effects of the mutual coupling during the optimization procedure. The use of a superstrate provides array structures with a reduced number of elements and enhanced aperture efficiency with respect to configurations without superstrate. The level of the grating lobes is also controlled during the optimization. A parametric study is performed to understand the capabilities of the leaky-wave-thinned array varying the reflectivity of the superstrate. As an example, an array of 18 elements working over a 7% fractional bandwidth is synthesized, providing a reduction by a factor of 4 in the number of elements when compared to a configuration with the same requirements, but without superstrat