Determination of optimum setting of primary feed ellipticity to obtain circular polarization from reflector type antennas

To effectively utilize circular polarization, we must be able to ensure that the radar antenna beam is in fact circularly polarized. When it is impossible to use a perfectly circularly polarized source we must use another method to obtain circular polarization on the secondary beam. If a primary feed is used that is circularly polarized on the peak of the beam but becomes elliptical off axis, then the secondary pattern will most likely be elliptical. A simple approach to determining the necessary primary feed ellipticity has been developed. The approach is applicable to reflector-type antennas whose contours are either totally or partially parabolic. Since a large number of radar antennas are in this category, the method is expected to find wide application. The new method involves measurement of the primary feed only, ad. simple conrputations to determine the optimum primary feed characteristics necessary to obtain circular polarization on the peak of the secondary beam. These results have verified the validity of this procedure for determining the optimum primary feed setting for obtaining circular polarization from reflector-type antennas.