Excitation peculiarity and frequency characteristics of spiral structures located on sphere-cylinder surface

In recent years more and more attention is given to elliptic polarization antennas for mobile terrestrial and space communications. A basic requirement of such antennas is obtaining a high value of polarization ellipticity in a wide sector of radiation angles. Spiral antennas located on a cylindrical surface allow one to obtain relatively high value of directive gain, however polarization ellipticity falls fast while deviating from the axis direction. On the other hand spherical structures have a high value of polarization ellipticity in a wide sector of radiation angles, but they are near-omnidirectional. A spiral antenna located on a sphere-cylinder surface is presented. It enables one to vary between directive gain and polarization ellipticity, obtaining the required relation.