Microstrip Archimedean spiral antennas are suitable for wideband satellite communications when CubeSat is used because of its light weight and small size. The wide band frequency response of the spiral antennas can be achieved by properly choosing their outer and inner radius .In this paper a spiral microstrip antennas are designed on FR-4, giving an ultra-wide band from 6-to-22GHz which covers all working satellite bands. High gain directive beam with suitable radiations in multiple frequencies for on-board satellite communications is obtained.