Satellite Communications

Abstract

Orthomode Transducers (OMTs) are passive microwave devices whose function is to discriminate between the two orthogonal single signals received by dual-polarization antenna systems. In transmission, they combine these signals and route them to the antenna (typically a horn-type antenna with revolution symmetry). Satellite communication systems and radio astronomy are typical environments where OMTs are found. Their use in communication systems allows to double the capacity of the system, since two different signals can share the same frequency spectrum, as long as they are associated to different orthogonal polarizations. This project is focused on OMTs in waveguide transmission systems. These devices have been developed over the last decades, though they are not widely dealt with in the literature. The design of these structures requires a good comprehension of some notions about electromagnetic theory and waveguides analysis. To set the framework of this project, a detailed bibliographic study of OMT components will be carried out. One of the most typical structures found in wideband OMTs is the so-called Turnstile junction. This particular structure holds some symmetry properties that grant a broadband performance. Among all the aspects involved in the design of a Turnstile junction, the design of its internal matching obstacle is one of the key elements. The aim of this project is to address an exhaustive study of all the components involved in the design of an OMT based on the Turnstile junction. For that reason, besides the theoretical study of electromagnetic concepts and the Turnstile junction, some routing structures such as bends, transformers and recombiners will be also studied and analyzed. Two complete OMT designs will then be carried out: the first one will follow some typical OMT specifications and it will include a new internal obstacle for the Turnstile junction based on mitered bends, proposed for the first time in this project; the second one will represent an effort to improve existing wideband OMTs performance. For the latter, the addition of a new degree of freedom for the Turnstile junction will be proposed. It consists of a configuration of angled branches for the junction, using the same obstacle of the first design. The aforementioned will result in a more compact structure with even better performance.