The aim of this study is to identify new RF payload output section architecture concepts for the forward link of the next generation of broadband multimedia payloads in Ka-band when using new enabling technologies and to assess and quantify their potentialities and achievable performances.
The main objectives of the study are :
- To identify techniques and technologies that will allow the definition of advanced and improved architectural concepts of RF payload output section for the next generation of broadband multimedia payloads in Ka-band,
- To assess the key features of the possible solutions, as well as the nature of improvements and benefits they can allow, their development and recurrent cost, and the time scale within which they become available,
- To identify and to evaluate the new RF payload output section architectures when using enabling techniques and technologies,
- To give a clear view on the benefits associated to the introduction of these techniques and technologies and to provide recommendations for development as well as priorities and risk areas.
Ka-band broadband satellites currently being developed represent a significant milestone in making the satellite recognizable as an important component of global telecommunication infrastructure. But there is still considerable effort needed to improve their efficiency and flexibility to support the trends toward high on-board capacity.
The next multibeam Ka-band satellites main issues are:
- On-board capacity increase,
- High flexibility (in terms of power, bandwidth, coverage, connectivity, etc).
To give a clear view on the benefits associated to the introduction of these new enabling technologies for the next generation of broadband multimedia payloads in Ka-band and to provide recommendations for development as well as priorities and risk areas.
One obvious trend of a communications network is system integration in order to provide subscribers with more upgraded services of high quality. These evolutions have pushed satellites into high performance communications systems. Hence multibeam antennas (MBA) have become a key component in satellite communications systems.
Conventional bent pipe Ka-band multimedia payload
|However, since most of the current MBAs are still using fixed beams, satellite service providers who are running fixed beams could face some business risks when the service environment changes. Hence, several manufacturers are studying the feasibility of a Ka-hand multibeam antenna based on phased array technology in order to provide coverage flexibility. The main difficulties for this kind of payload are on the transmit part.||
AFR antenna architecture
Based on an Alphabus platform (18 kW Power consumption, 1 000 Kg Mass for the payload) the following forward link output section payload architecture will be addressed showing the interest or not of the new enabling technologies:
- SFB (Single Feed per Beam),
- Advanced SFB (Flexible TWTA, MPA, etc),
- AFR (Array Fed Reflector),
- DRA (Direct Radiating Array).
The study is divided into three tasks. The general logic of the study is depicted in the following figure:
Task 1 defines the candidate technologies for all the main parts of the transmit output sections, including the beam forming networks (BFN), the high power amplifiers (HPA) and the radiating elements.
These new technologies will be compared to the currently used technologies in order to identify the benefits they could bring.
Task 2 defines payload output section advanced architectures that use the advanced technologies identified in task 1. The capacity of the different architectures to satisfy this reference scenario will be evaluated but, in parallel, the possible system scenario that can satisfy selected architectures will be addressed.
The task 2 will be divided in two parts :
Task 2a = this task will define the selected architectures and their detailed definition. It will include a reference architecture consisting in a state of the art SFB architecture. Advanced architectures will include SFB antennas associated to flexible TWTA, multiport amplifiers (MPA), array fed reflector (AFR), direct radiating array (DRA).
Task 2b = this task will address the impacts and the benefits of the chosen enabling technologies on the selected architectures. This will highlight the potential benefits and drawbacks of technologies.
- Task 1 Survey on candidate technologies: completed,
- Task 2a Payload output section definition and evaluation: completed,
- Task 2b Trade-off analysis and recommendation: completed.
The bottom up / top down approach conducted during the study has highlighted the potential benefits and drawbacks of technologies within the selected payload architectures for the reference scenario.
The work evaluates the maximum system capacity, which different flexible payloads using the Alphabus platform can provide.
Fixed coverage scenario (with passive/active antennas)
- The SFB reference payload is the best solution for high capacity payload if no or little flexibility is required,
- The Advanced SFB payload is the best solution for high capacity payload if flexibility (connectivity, power flexibility, power exchange between beams) at repeater level is required,
- The Advanced FAFR payload is not well suited for missions requiring high payload capacity.
The study has extended the results and recommendations to the possible use of technologies used for satisfying other scenarios (like missions requiring flexible coverage with low capacity).
Flexible coverage scenario (with active antennas)
- The flexible coverage capacity with an active antenna is antagonist to high payload capacity requirements,
- Due to low radiated C/I level generated by active antenna, the frequency re-use will be difficult to implement and only possible for user beams with large distance separation
- The trend is to use Mini-TWTA associated with 'low directivity antenna', having a few tens of radiating elements (like AFSR with 64 R.E) and to use GaN SSPA technology with 'more directive antenna' including a few hundred of radiating elements (like DRA with 320 R.E).
Nevertheless, in order to confirm this first trade off a strong development effort must be done concerning active antenna (AFSR and DRA) including architecture, accommodation constraints, thermal control, AIT constraints, calibration, etc.
The study has also provided recommendations on required technology developments, including priorities and possible risk areas.