Saving SWaP in Payload-Borne Phased Arrays with Multibeam Beamformers (Download)
Most common satellite communications were once based on geostationary (GEO) satellites, when only three satellites were required for global coverage. Then, launch vehicles would typically carry only one of these large satellites (>1,000 kg). While such deployments were beneficial for broadcast applications in television and radio, there were limitations.
One limitation is the latency involved in communications imposed by the great distance between the user and the satellite. Typical GEO orbits are near 36,000 km, which has an approximate end-to-end latency of 400 ms, approximately 10X higher than point-to-point fiber-optic connections in the United States. Secondly, while the GEO satellite covers much of the Earth, it can’t effectively cover its northern or southern poles. As an example, Inmarsat’s Global Xpress GEO satellites cover approximately ±75° off the equator.