Modélisation et optimisation des structures rayonnantes par des méthodes hybrides.

Abstract

In recent years, a significant number of studies have focused on microstrip antennas and dielectric resonator antennas because of their many advantages. Two main components formed the body of this thesis. The objective of the first part of the thesis is to overcome the limitations of the spectral approach by introducing artificial neural networks in the analysis of stacked microstrip antennas. The evaluation of the performances of the neurospectral model reveals a net superiority over the conventional spectral domain approach in terms of simplicity, speed and accuracy. To test the validity of the proposed technique, four configurations of the stacked antenna have been analyzed, built, and measured. Since our model combines both precision and speed of calculation, we expect that it will find extensive applications in the CAD of stacked microstrip antennas. In the second part of this thesis, significant efforts were also made in order to design a new antenna for GNSS systems. Since the envisaged application requires that the designed antenna must cover the entire frequency band of the GNSS system (1150-1610 MHz), we have opted for the choice of a dielectric resonator antenna as the basic element of our structure. The majority of communication satellites transmit signals using circularly polarized waves to benefit from the advantages offered by this type of polarization. It is then necessary that the antenna of the receiver be also in circular polarization. Four sequentially rotating vertical metallic strips, with the same amplitude and phase rotation of 0°, 90°, 180° and 270° have been used to feed to the proposed antenna, using in the feed network a broadband 180° balun structure linked with two 90° balun structures. A prototype of the proposed antenna was manufactured in the RF laboratory of the INRS in Montreal, Canada. The antenna has -10 dB reflection coefficient bandwidth from 0.97 GHz to 1.66 GHz of 52 %. The axial ratio is under 2 dB over a large frequency band from 1.08 GHz to 1.78 GHz of 48.9%. The measurements have also shown that the maximum achieved gain peaked around 5.2 dB at 1.4 GHz, and remained above 2.75 dB over the entire band of the GNSS application. The proposed antenna covers the GNSS bands including the GPS, GLONASS, Galileo, BeiDou as well as the Indian Regional Navigation Satellite System (IRNSS) and the Japanese Quasi-Zenith Navigation Satellite System (QZNSS) bands. With these features, this antenna could be mounted for navigational use on vehicles or ships.