European Space Agency

XBDL Compact High Speed X-band Downlink


The project is developing an X-band transmitter (8.025GHz to 8.4GHz) using a high-speed baseband processor, coded and modulated to the latest CCSDS standards, in a compact highly integrated and power efficient design. The modulation drives a nonlinear SSPA followed by an integrated post-amplification RF shaping filter (as specified by ECSS-50-05C). Such an approach offers high efficiency at high data rates with low risk. In addition to this mode of operation, the system architecture readily supports linear modulation scheme such as QPSK. 

To meet parallel to serial data stream processing as well as baseband processing the intention is to leverage the latest commercial FPGA technology, including commercial IP cores where needed. 

The project takes an evolutive approach that will allow a stepped development to more advanced coding & modulation techniques. 

The result is a more flexible, software configurable product designed to give mission assurance with optimised cost of ownership for the evolving small sat world.

Picture credit: COM DEV Europe Ltd, Heritage C-band product


The key challenges are in appropriate component selection for the given design philosophy and the system architecture choices to meet the exacting radiation, thermal, mechanical and electrical environmental factors, while maximising product functionality and configurability. Key experiences in flexible TT&C and heritage flight datalink products, where pragmatic qualification approaches were validated are essential to development success. Our development also requires inputs from as many potential users as possible to ensure that its capabilities meet customer needs.


The software defined architecture allows for reconfigurability and fine tuning to individual end customer needs. Software configurability also enables:

  • flexible modulation
  • flexible data-rate
  • flexible output power

 Connecting the baseband processor directly to an X-band modulator and subsequent high power high-efficiency GaN based power amplifier delivers savings in mass, power and volume. 

  • Software defined radio (SDR) based implementation
  • Non-ITAR commercial-off-the-shelf (COTS) components
  • Low mass and low volume unit
  • Programmable output frequency
  • Selectable coding
  • High efficiency Gallium Nitride (GaN) amplifier-based design for low power consumption

This solution is aimed at missions in low earth orbit (LEO) with a balance of affordability, flexibility and total cost of ownership in mind, enabling smaller, lower cost, more agile platforms in our evolving industry.


Units are built in accordance with ECSS class 3 (NASA level 2) standards taking a radiation tolerant rather than radiation hardened approach to deliver mission assurance. 

  • Low mass, low volume unit
  • SDR based implementation with flexible modulation, data rate and output power
  • QPSK/8PSK modulation schemes
  • Programmable output frequency
  • LVDS synchronous data ports with auto detection
  • Low power consumption
  • High efficiency GaN amplifier based design.

 Full product specification is available from

System Architecture


  • MS1 PDR: Architecture development, Concept development & breadboard design
  • MS2 CDR: detailed design and MAIT of EM unit
  • MS3 TRR: EQM MAIT, test system development and release
  • MS4 FR:  Qualification of EQM and development.

Current status

Project KO meeting held Aug 2018, early preliminary design presented with work ongoing towards PDR.

Status date

Monday, January 28, 2019 - 11:00