Current spacecraft antenna design must confront the problem of how to mount and deploy large reflector antennas on spinning platforms. The reflector spins at approximately 10 to 40 rpm to cover the desired scanned area on Earth. One solution - a back-to-back reflector antenna with a reduced moment of inertia - has been proposed by Keyvan Bahadori and Yahya Rahmat-Samii from the University of California, Los Angeles (UCLA).When both back-to-back reflectors are utilized, this configuration vows to reduce the spinning speed by half for a given sampling rate.
The reflector's geometrical patterns are determined so that the rotating system's moment of inertia is reduced. These back-to-back reflectors suffer from a high cross-pol level in the asymmetrical place due to the large feed offset angle. To minimize that cross-pol level, a sub-reflector can be used to satisfy the Mizugutchi condition. Alternatively, a tri-mode matched feed horn can be utilized. See "Back-to-Back Reflector Antennas with Reduced Moment of Inertia for Spacecraft Spinning Platforms," IEEE Transactions on Antennas and Propagation, Oct. 2007, p. 2654.