X Band Downlink for CubeSat: From Concept to Prototype

TLDR: A first high performanc e X band transmitter was developed by Syrlinks in 18 months for CNES and ESA for PROBA-V mission and the development of a highly integrated micro transmitter, with a form factor and consumption compatible with 3U CubeSat or NanoSat is studied.

Abstract: This paper starts with a remind of the main perform ances of the transmitter which is able to modulate data up to 50 Mbps (up to 100Mbps with technical restriction), deliver 2 Watts with no more than 10W DC/DC consum ption in only 0.3U dimensions. Then, the architecture of the transmitter is presented with all the key function s such as the power amplifier, synthesizer, IQ modulator, filters . Some results achieved on the prototype are presen ted with particular attention to the consumption, BER measur ements and transmitter quality losses. The process used to select and qualify the key components is also described. INTRODUCTION Today, more and more complex and miniaturized payloads for CubeSat or NanoSat are in development for earth observation, astronomy or space spectrum survey missions. Such instruments generate large amount of data and require much higher data rate telemetry solutions than those which are currently available. If UHF and S bands are well adapted to usual teleme try needs, the channel bandwidth which is limited to maximum 6 MHz in S band can hardly fit with future high data rate telemetry needs, even with high spec tral efficiency options. In these conditions, X band appears to be a good solution as the gain at system level is really sign ificant, in particular with variable bit rate option. Nevert heless, the feasibility of such subsystem for CubeSat is no t trivial because the energy and size are again more restricted than on micro satellite platforms where X band is already tricky. Fifteen years ago, the design of S band equipment w ith COTS was a real challenge because most of the exist ing ground wireless applications were limited to UHF. Today, many wireless applications exist up to 5-6 G Hz. But only a few are located close to 8-9 GHz and alm ost no highly integrated chipsets exist that could ease the design of a miniaturized X band telemetry transmitt er. Despite these difficulties, a first high performanc e X band transmitter was developed by Syrlinks in 18 months for CNES and ESA for PROBA-V mission. In the follow up of this development, Syrlinks has started to study for CNES a highly integrated micro transmitter, with a form factor and consumption compatible with 3U CubeSat or NanoSat. The miniaturization is achieved both thanks to smar t choices of modulation, coding and architecture but also to a selection of high performances circuits and components. After the development of a first prototype which ha s showed promising performances, an Engineering Model realisation is now on the way. It will be followed by a qualification campaign. The qualification tests will be executed both at component level for the most critical parts and at the board level for rest of the equipment. The system aspects were already exposed in referenc e 1 where link budgets are presented. They show the capability of this solution to download several gigabytes per day with 3.4 or 5m diameter antenna ground stations and with 0 dBi gain board antenna.