The use of frequency modulated continuous wave (FMCW) radars is quite widespread in military applications and tank level measurements. In my thesis, I designed a horn antenna for a radar detection system. During my work I conducted analytical calculations in order to determine the properties of a pyramidal antenna with ideal aperture, and those of a general pyramidal antenna with phase error. With simulational tools I examined the radiation pattern and the input reflection of a horn antenna with the calculated dimensions. I considered the possibilities for the correction of the second order phase error, where I mentioned the effects of metal plate, hyperbolic and elliptic lenses as well as their potential problems and weaknesses. I also looked into the different methods for edge diffraction. In the next phase I used tuning screws to correct the reflectional problems that emerged during the first tests of the antenna equipped with the elliptic lenses. In the course of the project my main goal was to obtain the defined parameters, but at the same time I was trying to find the most cost-efficient and feasible solution. The final part of the design was the tolerance testing of the antenna in the 0-80 °C temperature range, which yielded positive results. Finally, I studied different manufacturing processes seeking for the optimal method, providing a short comparison at the and of my paper.