Ku-band spot beam antenna for the Intelsat VIIA spacecraft

Intelsat VII is the seventh-generation telecommunication satellite designed to provide a global community of well over 100 nations with satellite communication capabilities. The three-axis, body-stabilized satellites will be positioned above the Atlantic, Pacific, or Indian Oceans, thus linking the adjacent continents via multiple antenna beams. A major modification to that satellite is termed Intelsat VIIA, which resulted in a contract award to Space Systems/Loral by the International Telecommunications Satellite Organization (Intelsat) in December 1990. The Intelsat VII baseline Ku-band spot beam antennas termed S1, S2 and S3 were replaced on Intelsat VIIA with dual polarized antennas that permit frequency reuse operation. Two transponders which operate on new polarizations were added in the S1 and S2 coverages. This increased the total number of simultaneously operating transponders to 14. The new transponders can be individually switched by ground command for operation in the 10.95-11.2, 11.45-11.7, 11.7-11.95, or 12.5-12.75 GHz frequency bands. The paper describes in detail the design of the most complex of these spot beam antennas which is called S2. The RF measured radiation amplitude patterns of the prototype hardware is shown. The excellent correlation achieved between the measured and computed results substantiates the quality of the hardware design. The primary electrical performance requirements driving the antenna design are outlined