Septum polarizer design for antenna feeds produced by casting

Many septum polarizer components are manufactured by casting. A parameter inherent to this production process is the draft angle, which leads to a linear reduction of housing dimensions with component length and which has been neglected in many polarizer designs over the years. With 25 dB return-loss/isolation and 0.5 dB axial-ratio specifications, however, the draft angle can no longer be neglected, since a slight increase in, e.g., septum thickness can already result in a considerable performance degradation. Therefore, this paper takes the casting manufacturing process fully into account. Moreover, matching transformers are incorporated under the same restrictions.