This thesis is framed in the context of advanced waveguide antenna feeders. More speci cally, it is devoted to the development of modelling techniques that can be applied in the design of new antenna systems, either to increase the performance of already known antennas or to create designs with completely novel characteristics. To achieve this goal, the thesis is divided into three main parts: 1) computation of the radiation pattern produced by radiating apertures and radiation pattern synthesis in apertures, 2) quasi-analytical horn antenna simulation and its application to horn antenna design, and 3) innovation in other non-radiating devices used in antenna feeders. The two pillars that sustain the modelling ideas presented in this thesis are the radiating aperture eld equivalence principle, which relates the aperture electromagnetic eld distribution to the far-zone radiated eld, and the waveguide modal eld expansion, which allows to express any aperture eld distribution as a weighted summation of modal eld functions. Thanks to the combination of these two concepts, the total radiation pattern produced by the aperture can be expressed as the weighted summation of the radiation patterns corresponding to each of the modal eld functions that exist in a waveguide with the same cross-section as the aperture. One application of this analysis approach is the synthesis of an aperture eld distribution that generates a radiation pattern with certain speci ed characteristics, including the speci c case of monopulse di erence patterns. This radiation pattern calculation strategy can also be used for the fast analysis of horn antennas. The mode-matching method is a waveguide device analysis technique well-known for providing accurate results and being computationally e cient. By a modematching analysis of the horn pro le it is possible to determine the electromagnetic eld distribution at the horn aperture, from which the radiation pattern produced by the horn antenna can be obtained. The accuracy of this analysis strategy is comparable to that achieved by general purpose numerical tools, but the computation time is signi cantly reduced. Therefore, this mode-matching analysis can be e ciently integrated with an optimization routine in order to tune the design parameters of a horn pro le. To show the usefulness of this optimization scheme a sophisticated W frequency band monopulse horn feed with a triple radiation pattern is designed. Finally, the design of two innovative waveguide devices is presented: a recon gurable phase shifter completely implemented in waveguide technology and a compact circular polarizer. Although they are not directly responsible for radiating or receiving electromagnetic waves, these devices also play a key role in the feed chain of many wireless applications like radar, phased arrays or satellite communications among others.