Best Paper Award

  In recent years, even small cameras or sensors that can be mounted on small satellites weighing less than 100 kg have high capability for earth observation. As social demand for disaster risk management and environmental monitoring increases, great attention is being paid to small satellites which require shorter development periods and lower budgets.
   In order to expand the application scope of small satellites, high-capacity downlink telecommunication is needed to transmit large amounts of observation data from high-performance sensors. But, such earth observation satellites are generally in low earth orbits at altitudes of several hundred kilometers; thus, we have, at most, only 10 minutes of communication window.
   Therefore, we have developed a high-speed X-band downlink transmitter for small satellites. By using this higher frequency instead of conventional S-band, we can get a wider frequency band and use a small middle-gain antenna (MGA) that can be easily mounted on a small satellite. However, in order to make efficient use of frequency which is a limited resource, multi-level amplitude phase modulation, which is more complicated, must be used. Gallium nitride high electron mobility transistors (GaN - HEMT), which lately have evolved to a significant degree, enabled us to design a highly efficient solid state power amplifier (SSPA) system. As a result of its stable low distortion characteristics, we successfully overcame the disadvantage that multi-level amplitude phase modulation requires high power consumption for signal quality, without a complicated signal quality compensation system.
   Our transmitter can be efficiently mounted on small satellites with low power and weight resources. Weight: Approx. 1.3 kg; Power consumption: Approx. 22 W, with multiple modes for experiments. We carried out a reception experiment with a ground-based 3.8 m class antenna mounted on a 60 kg class earth observation satellite and obtained a bit rate of 348 Mbps, including error correction by turbo code.