It would depend on what you have in mind. For just a basic communications satellite, a probe or advanced probe (depending on the capability you envision) makes a good model. This would be part of a constellation - probably about a dozen would be needed to provide (basic) worldwide coverage, with more satellites providing more thorough and higher (effective) bandwidth communications. A larger, more capable installation, capable of covering and enhancing communications for a roughly continental range, could be designed using the Robots and the Vehicles handbooks, and High Guard could be used to design a 10 or 100 Dt space station (even an unmanned space station) to handle global telecommunication over a quarter or more of the globe, maybe over the entire thing with smaller satellites to act as over-the-horizon relays. In fact, most technologically advanced worlds are probably going to handle their telecommunications networks with a tiered approach of this nature, probably having two or three of the space station facilities (for redundancy - one of these is quite likely enough to handle the bandwidth for a world, but having a backup is going to be considered the intelligent approach), with dozens or hundreds of the smaller satellites to act as relays.