High Power Transmitters for Q/V-Band Communications-Beyond Alphasat

Since the delivery of the Q-band Solid-State Power Amplifiers (SSPA) for Alphasat TDP5 in 2012 and their successful operation in space for over 5 years, very significant advances have been made in the technology and design of SSPAs thereby greatly enhancing their performance, suitability and reliability for space payloads. The most important of these developments is the improvement in the capabilities and maturity of Gallium Nitride (GaN)-based MMIC power amplifiers in Q/V-bands and higher. Other critical factors include innovative circuit integration techniques, novel manufacturing methods and advanced materials. Given the same mechanical outline, the emerging technology can generate more than four times the power output, two times the efficiency and an order of magnitude higher reliability than the original Gallium Arsenide (GaAs) MMIC-based SSPA for Alphasat Q/V Communications payload. Newly developed GaN MMIC power amplifier devices can generate two-to-three times the RF power output at twice the efficiency of their GaAs counterparts in the same frequency range thus increasing the power output per unit volume by a large factor while lowering the DC power consumption. Furthermore, GaN devices can operate at much higher channel temperatures (>165 deg. C) with reliability (MTTF) consistent with long-term (>15 years) use in space equipment. In this paper, we will present a design concept that is capable of generating 50 to 100 Watts of RF power over the 37.5-42.5 GHz band with power-added efficiency approaching 25-30% within approximately the same outline and weight as the original Alphasat SSPA. Highly efficient, robust and compact power combining methods developed for this family of SSPAs make use of novel materials and manufacturing processes to further enhance the capabilities of the Q-band SSPA. Another useful feature of the approach adopted for the SSPAs is modularity of their construction, which allows rapid development and manufacture of customized transmitters for various payload requirements.