Design and modeling of circularly polarized conical beam antennas for space missions

Space missions present antenna designers with a unique set of requirements. Not only does the antenna need to perform optimally from the electromagnetic radiation point of view, but also need to survive launch conditions, perform optimally at extreme temperatures, deter ionizing radiation, and provide electrostatic protection. Furthermore, without any prospect of repair, such antennas need to be robust enough to withstand the harsh environment on its own. This thesis work touches upon such multi-physics approach to antenna design. More specifically, the antennas concern the ones for the Lander Radioscience (LaRa) instrument intended for the surface platform of the ExoMars 2020 mission to Mars. The antennas would allow direct communication with Earth irrespective of the orientation of the surface platform when it lands, and allow observation throughout the year. This is possible through the conical radiation patterns, which have uniform elevation pattern over the azimuthal plane along the surface platform. For space communications, it is a necessity to have circular polarization as well. Therefore, the thesis proposes different topologies of circularly polarized conical beam antennas ideal for space communications, from planar antennas to 3D metallic antenna. Concerning the planar antenna technology, a circular slot array and a circular patch antenna were developed. The multi-layered PCB structure requires a careful design given the need for space qualification, due to the thermoelastic effect. Metallic antennas are deemed more appropriate to counter such effect, since the homogeneous material properties of the metallic antennas ensure better performance under the thermoelastic stress. To that end, a novel 3D metallic antenna is proposed which is based on gamma-shaped vertical posts surrounding a centrally radiating monopole. Moreover, a numerical method to analyze the near-field performance of the antenna has also been proposed. Especially in the case of space antennas, whose level of detail requires a dense mesh, the proposed method is effective. The method aims to improve the near-interactions in the well known Method of Moments (MoM) by making the integrals separable with respect to source and observation coordinates. This approach opens new avenues for fast electromagnetic analysis of complex structures.