Developpement de composants SIW dans la bande 3 d'ALMA (84--116 ghz) et conception d'une jonction OrthoMode (OMT) dans la bande 1 d'ALMA (31--45 ghz) en technologie guide d'onde

The first section of this thesis is to determine which would be the best option from the available substrate integrated circuits (SICs) for use in applications in the field of the millimetre-wave radio astronomy. The substrate integrated waveguide (SIW), whose vertical electric walls are synthesized by two rows of metalized holes made using a laser, has proven to be a good choice in terms of insertion losses and bandwidth compared to the Substrate Integrated Non-Radiative Dielectric (SINRD) and Substrate Integrated Image Guide (SIIG). After having chosen the SIW technology, a very precise and quick method, taking into consideration the losses due to radiation and the presence of stopbands, due to the periodic nature of this structure, was proposed to design SIW guides. Next, wideband SIW passive components were designed and manufactured. The operating frequency of these passive circuits is in the 84 to 116 GHz bandwidth, which corresponds to Band 3 of the ALMA project. Using the same RF architecture as the Band 3 RF circuit, which was developed by the millimetre wave group of HIA-NRC Victoria and using the waveguide technology, we proposed two wideband SIW couplers with a coupling factor of 3 dB and 23 dB, respectively, an SIW power divider and a termination for SIW guides. Performances were compared with those obtained with the equivalent RF circuit developed using waveguides (WR–10). In order to evaluate the RF performance of SIW circuits designed, a back-to-back transition from SIW to rectangular waveguide (WR–10) guide was designed in the 75–115 GHz band.;Two ALTSA (Antipodal Linearly Tapered Slot Antenna) planar antennas fed by an SIW line were also developed. The operating bands for these antennas are: 21–30 GHz, and 90–115 GHz. It was shown that if the antenna's parameters are chosen correctly within this final frequency band, an average gain of 15 dBi—a difference of almost 24 dB between the main and secondary lobes—a cross-polarization level of about 20 dB in relation to the main lobe, a difference of less that 7 ° between the main lobes and H plane and E at −10 dB, and finally, a matching at the antenna input better than –20 dB can all be achieved. The antennas presented are very efficient and are a viable planar alternative to traditional horn antennas. A transition from an SIW guide toward a microstrip line was designed to allow the measurements of the 21–30 GHz antenna. The transition is wideband with minimal radiation losses. A transition from SIW toward WR10 waveguide was used in order to measure the RF performance in the 90–115 GHz frequency band.;The promising results achieved with SIW planar technology proves its aptness with regard to traditional technologies, such as the microstrip and CPWs lines, to operate in the millimetre band, over a large bandwidth and with very low insertion losses. The flexibility offered by SIW technology offers, when combined with planar antennas a good candidate for the next generation of radio telescopes.;The last objective of this thesis was to design an OMT (Orthomode Transducer) prototype—a diplexer which allows the separation of orthogonal polarisations within the same frequency band and within Band 1 of the ALMA project, 31 GHz to 45 GHz. This said band will permit, among other things, the detection of HC3N and OH molecular lines or even the spectral line of silicon monoxide (SiO). The OMT was designed using the waveguide technology with the aim of considerably reducing the insertion losses when it is operated at 15K. The specifications were defined as follows: matching at the input and outputs of the OMT of at least –25 dB, isolation between the two polarisations higher than 40 dB and insertion losses lower than 0.3 dB. (Abstract shortened by UMI.).