four arm feeding network
iearch it in basic book of antenna and net
The effects of antenna shape and the feeding network on the cross-polarization discrimination of four-arm planar antennas are examined using a novel characteristic parameter, the polarization stability factor; this quantitiy is considered for both the four-arm planar Archimedean and logarithmic spiral antennas. It is shown that, if the size of the antenna is sufficiently large, high values of the polarization stability factor, which allow the radiation of very pure circular polarization with no need for extremely optimized feeding networks, can be obtained.