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Original Publication Date: 2001-Mar-16
Included in the Prior Art Database: 2001-Mar-16
Document File: 3 page(s) / 10K

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Roger Dendy: AUTHOR [+1]



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This is the abbreviated version, containing approximately 43% of the total text.


by Roger Dendy and Bob Frederick


In Satellite Communication Systems, the number of users which can be supported depends on the critical parameters of payload size, weight, and power (SWAP). Modern multi-beam satellites achieve increased capacity through frequency reuse, and it is desirable to maximize the number of beams within the SWAP constraints.

In a multi-beam satellite system, the number of beams that can be served depends not only on antenna technology, but also on the number of travelling wave tube amplifiers (TWTA) which can be accommodated within the size, weight, and power budgets for the satellite bus.

In addition to the primary TWTAs serving each beam, it is necessary to have an adequate number of redundant TWTAs to ensure that the system's users can be served in the event of a TWTA failure and system availability is ensured.

In conventional satellite systems, redundant TWTAs are connected to the antenna through a network of wave-guides and semi-static switches. These semi-static switches are intended for switching only on the failure of a TWTA, and are not capable of extremely fast or repeated switching.

Some satellite systems, notably the experimental Advanced Communications Technology Satellite (ACTS) developed by the National Air and Space Administration (NASA), include fast ferrite-switch beam-hopping technology, which allows a single TWTA to serve multiple beams.

This publication describes a scheme to enable all the beams to be served in a beam-hopping satellite system, without requiring an excessive number of spare TWTAs needed for redundancy and system availability.


Prior art beam-hopping switches, such as those employed on NASA's Advanced Communications Technology Satellite (ACTS), enable one TWTA to be rapidly switched between two RF paths, leading to either of two antenna ports, or alternatively to a second switch. By cascading several layers of 1x2 switches, ACTS can serve over 20 beams with a single TWTA.

The current invention alters this approach by connecting two TWTAs to two antenna ports via a 2x2 switch, as shown in Figure 1. During normal full capacity operation, the switch remains static and each TWTA serves its respective beam. In the event of a TWTA failure, the single remaining TWTA can be rapidly switched between the two beams.

In this configuration, the capacity per beam is reduced by half, but neither beam is disabled (Figure 2). Thus, the satellite service is maintained without requiring extra redundant TWTAs.

If the traffic demand is not identical between the two beams, the per-beam dwell time can be adjusted accordingly. In this way, the per-beam capacity is tailored to meet the user demand while optimizing the efficiency of TWTA resources for different traffic profiles.

In addition to providing a failure...