As the project progressed, the final architecture of the payload communications subsystem were finalized. The payload communications subsystem encompasses Ku Band Downlink, X Band Downlink, and S Band Bidirectional links. In particular, it was necessary to identify the relevant interfaces that the Spacebourne communications payload would use to communicate with the rest of the payload systems, as well as the bus itself. Power also had to be provided for the communication subsystems.

Defining these interfaces are essential to successfully integrate the communications payload into the satellite

At the heart of the systems lies the Link SX radio. The radio is controlled via the bus wide CAN bus, with the CSP protocol. Payload data is transferred to/from the payload computer through a bidirectional Spacewire Link; a secondary redundant link is provided through RS422, albeit at a slower pace.

The Link SX out generates a Intermediate Frequency with modulated data at 1150 MHz. This is routed either to the S, X or Ku Band radio front ends. In the case of S Band, data is modulated according to the CCSDS standard. For X and Ku Band, the data is modulated according to the DVB-S2 standard, with an encapsulation method that is proprietary to Gomspace (known as the Gomspace Stream Encapsulation, GSSE). This differs from Generic Encapsulation and the standard MPEG Transport Stream Encapsulation.

The S and X segments provided by Gomspace upconvert and amplify the IF signal to the correct RF frequency for transmission. The Ku band segment is developed inhouse, and is the subject of this report. The Ku Upconverter segment is controlled by an SPI interface, which configures the correct LO frequency for transmission. The IF is then mixed and Ku band RF is generated, which is fed to the HPA which drives the Ku band patch antenna. The upconverter board also provides attenuated coupled RF outputs from the LO lines and the post mixing stages, for functional testing and diagnostics.