The present invention relates to a communications satellite transmission and reception architecture that includes phased array antennas. In particular, the present invention relates to a satellite payload that coordinates a transmit phased array antenna, packet switch, and a receive phased array antenna.
Satellites are a common feature of modern communications networks and have long provided communications services on a global scale. A communications satellite often flies in a geostationary (GSO) orbit (at approximately 35,784 km altitude with an inclination and eccentricity of zero) so that the satellite always appears in the same spot in the sky. Satellites, however, may also be placed in other orbits, including Non-geostationary orbits (NGSO).
A NGSO satellite typically orbits between 250 and 12000 km above the Earth. NGSO satellites orbit the Earth independently of the Earth's own rotation and therefore do not maintain a constant location in the sky. Because the orbit of a NGSO satellite periodically takes the NGSO satellite over various locations on the Earth, the NGSO satellite may be used to provide periodic communications services to those locations. A constellation of many NGSO satellites may be used to provide nearly continuous coverage to virtually all areas of the Earth.
As an example, Teledesic LLC, located in Kirkland Wash., United States, has proposed a NGSO constellation referred to as the Teledesic Network which flies 288 NGSO satellites. The Teledesic Network incorporates 12 orbital planes with 24 NGSO satellites per plane. Each orbital plane is approximately perpendicular to the equator and separated from adjacent orbital planes by approximately 15 degrees. The altitudes of the satellites in each orbital plane are staggered so that the satellites pass below and above one another at the North and South poles, where each orbital plane converges.
Two sets of intersatellite links (ISL) connect the satellites in the Teledesic Network. North-South links provide continuous connections between the satellites in individual orbital planes. Any first satellite in an orbital plane has a connection to a second satellite ahead of its current position and a third satellite behind its current position. Similarly, East-West links provide a connection between the satellites in a first orbital plane and the satellites in a second orbital plane and a third orbital plane on either side of the first orbital plane (the adjacent orbital planes).
In the past, satellite antenna technology has provided GSO and NGSO satellites with Multi-Beam Antennas (MBAs) which provide transmission and reception of fixed size and direction beams. Because the MBAs are fixed, the satellite using an MBA antenna cannot adjust its antenna pattern to accommodate the variations in user demand in a region of interest (ROI) as the satellite moves overhead. For example, an MBA pattern setup to cover the United States would not efficiently cover South America.
As a result, satellites in the past have required payloads using complex configurations of MBAs. Each MBA is selectively activated or deactivated to provide coverage for a ROI as the satellite moves from one ROI to another ROI. The complex configurations of MBAs require the satellite to include a complex switching network to activate and deactivate the MBAs. Furthermore, the complex switching network and additional MBAs increase the power demand on the satellite's limited power supply as well as drive up the size and weight of the satellite (making the satellite more expensive to build, transport, and launch).
In the past, satellites have attempted to cope with the complexity of MBA design by purposefully creating payloads with sub-optimal MBA configurations using fewer MBA components. Because an MBA design providing optimal coverage for one ROI generally results in very poor coverage for the other ROIs, a compromised, sub-optimal MBA configuration is typically used. The sub-optimal configuration reduces the complexity of the MBA design and relieves the very poor coverage for the other ROIs by providing sub-optimal coverage for all ROIs. The sub-optimal configuration also reduces the amount of communications capacity available to the ROIs and thereby limits the amount of information that may be transmitted and received as the satellite moves overhead. Revenues are correspondingly reduced.
A need has long existed in the industry for a satellite payload design that eliminates the added complexity, power requirements, and cost of complex MBA configurations.