The present invention relates to satellite beam patterns. In particular, the present invention relates to overlapping beam patterns that support the bandwidth requirements of non-uniform population distributions.
Satellites carry antennae that provide communications bandwidth between the satellite and a region of interest (ROI). The ROI, for example, may include the entire United States, or any other selected portion of the Earth. Because many ROIs, including the United States, have a non-uniform population distribution, it is often the case that areas of a particular size within the ROI have much greater bandwidth requirements than equal sized areas elsewhere within the ROI.
In the past, however, satellite antennae have either produced a single beam which covers an entire ROI, or have produced a set of equal sized beams laid out on a regular grid pattern to cover the ROI. The past approaches to beam coverage have a number of undesirable characteristics. First, the bandwidth provided by the beam coverage may not be adequate for areas of high bandwidth demand (generally corresponding to areas of high population density). Thus, suppliers of communications services, for example, Internet service providers or cable TV operators in a particular Nielsen region, cannot establish accounts with consumers who might be willing to pay for those services. Similarly, the bandwidth provided by the beam coverage may greatly exceed the bandwidth need in sparsely populated regions. As a result, bandwidth which may be needed elsewhere is wasted.
Furthermore, when a grid pattern is used, the portion of the frequency spectrum (typically selected from the K or C frequency bands) occupied by the beams simply alternates across the grid. As a result, prior beam patterns required transmitting the same information on several beams to cover a wide area. For example, in the West, a particular market region may be much larger than a single beam. The same information must, therefore, be transmitted on several beams that cover the market region. As a result, the amount of bandwidth provided in a grid pattern may be more than twice the amount actually necessary to support the total bandwidth demand.
The inability of prior antenna to produce efficient beam coverage for non-uniform populations is a result of beam pattern design tradeoffs including antenna size, coverage area, and power limitations. Production of smaller, tightly focused beams for densely populated areas, sometimes referred to as spot beams, requires a very large antenna. Very large antennas, in turn, are expensive to manufacture and launch, and require more power during operation the most conventional satellites can generate. On the other hand, a smaller antenna may be used to produce a larger beam, but the larger beam cannot focus its bandwidth on a small area of high bandwidth demand.
As a result, it is desirable to project a beam pattern on the ROI which uses numerous beams of various sizes to provide the appropriate bandwidth for each area in the ROI. In other words, a set a tightly focused beams (referred to as "spot beams") might be directed towards areas of high bandwidth density, while a smaller set (or even a single beam) of less tightly focused beams might be appropriate for a much larger area with a lower bandwidth demand (for example, some of the sparsely populated Western states). Directing the appropriate amount of bandwidth to the appropriate areas results in less expensive, more efficient, and less complex beam pattern coverage. Appropriate beam pattern coverage also tends to create more communications services available at a lower cost to more individuals.
Therefore, a need remains for improved antenna beam patterns which overcome the disadvantages discussed above and previously experienced.