In this thesis, a set of software tools for improving and speeding up the predesign phase in antenna design workflow has been designed based on theoretical formulation. During an internship at IDS S.p.A, a number of Python-based tools have been developed and integrated in the software Galileo EMT, the electromagnetic toolkit of the CAE suite produced by IDS S.p.A. Initially, the theoretical design criteria of rectangular microstrip antennas, rectangular horn, double ridged horn antennas, archimedean spiral, equiangular spiral antennas and a microstrip to parallel stripline balun to feed spiral antennas have been analyzed. After the implementation of the tools, a design validation has been done through full-wave simulations, comparison with commercial products or scientific papers, prototypes and measurements. Furthermore, a cavity-backed spiral antenna for GNSS applications has been designed by using the proper developed tool. The proposed antenna was designed for direction finding application in L frequency band for GNSS monitors, context in which IDS S.p.A. realized a product to meet the new requirements set by the ICAO recommendations for civil air navigation systems.