Horn antennas are widely used in communication systems. They are typically used as feeds for re ector antennas and, due to its robustness, they can also be mounted on the fuselage of airplanes and are used on-board satellites. Horn antennas also present great directivities, gains, and e ciencies. The main drawback of this antenna family is (as it happens with most microwave devices) that they are complicated to simulate with full-wave electromagnetic methods. Most of the commercial tools available at the market for simulating microwave devices (CST Microwave Studio, HFSS,…) use general numerical methods such as nite elements or nite di erences in time or frequency domain, whose main advantage is that they can tackle a wide range of problems. The main drawback of these general methods is that this generality makes the simulation ine cient, causing long computation times for some problems in comparison with other more analytical techniques. This leads to the rst goal of this work, which consists in developing a software tool capable of analysing, simulating and designing horn antennas e ciently based on a numerical method, called Mode-Matching, which is known to be very e cient for this type of problems. In order to compute the radiation pattern of the antennas, the radiation integral of the electromagnetic eld at the horn aperture has to be calculated. An important part of this work will be devoted to the derivation of the necessary formulas that will allow to compute these integrals, since the literature does not usually cover these derivations with enough detail (typically the integrations are just solved for a simpli ed case), while here we will address the complete modal excitations. The use of this software would not only lead to shorter simulation and design times but would also permit to design horn antennas using low/moderate performance computers like notebooks. The construction of horn antennas (and once again, of most microwave devices) is usually a process with a high economic cost. But in the recent years, additive manufacturing techniques like 3D printing have opened the door to the low cost manufacturing of three-dimensional structures. Therefore the second goal of this work is to develop a construction process for the prototyping of horn antennas using a 3D printer. This process must be fast and inexpensive. To test the validity of these manufacturing techniques di erent devices will be constructed like conical, pyramidal and choke horns. In addition hollow and gap waveguides will be also studied and their performance will be evaluated. The fabrication of these devices will be performed locally by the author of this work. Moreover, the resulting devices will be also fully experimentally characterized in this work, in order to compare their characteristics with the simulations performed using the developed models. This will produce a convergence of the two goals of the work, joining the advanced electromagnetic modelling of microwave devices with one of the newest and trendiest manufacturing techniques.