W-band Airborne SATCOM Power Amplifier

ABSTRACT:QuinStar proposes to develop an efficient, linear solid-state power amplifier (SSPA), operating over the 81 to 86 GHz band, for high data rate communications between Unmanned Aerial Vehicles (UAVs) and satellites. We will accomplish this by employing state-of-the-art wide-bandgap gallium nitride (GaN) HEMT devices in conjunction with several circuit innovations. First, we will employ a quasi-switching mode of operation for the MMIC amplifier to improve its efficiency. Phase I results presented in this proposal indicate that with this technique, drain efficiencies of up to 71% are possible. Second, we will utilize Envelope Tracking (ET) and Digital Pre-Distortion (DPD) to linearize the resulting switching-mode amplifier and extend its efficiency over a wide dynamic range. During Phase I, we demonstrated the power and versatility of this approach by using measured GaN MMIC data in conjunction with simulations. We were able to improve the amplifier average efficiency by more than a factor of 3, while simultaneously meeting the -36 dBc ACPR linearity requirement. Finally, to realize the 50W power levels required, we will employ innovative power combining techniques. We are proposing a 2-tier, 64-way combining structure with the 1st tier consisting of a new 4-way combining network and the 2nd tier, a 16-way radial combiner. With this combination, simulations indicate an overall 85% combining efficiency.BENEFIT:Future warfighters will require increased SATCOM capacity for improved situational awareness. Current SATCOM bands are already overly congested indicating the need to exploit nontraditional frequency spectra, such as the E-band up and down links at 81-86 GHz and 71-76 GHz, respectively. This proposal addresses the uplink requirement by proposing a 50 W high-efficiency linear power amplifier for the transmitter. High efficiency is required to reduce the UAV prime power requirements and to reduce self-heating. This, in turn, will increase the amplifiers reliability or lifetime (MTTF). Linearity (-36 dBc ACPR) is required in order to handle advanced spectrally efficient modulation schemes, such as 32-QAM, without distorting the information or generating adjacent channel interference. In addition to SATCOM UAV applications, this linear, high-efficiency SSPA technology can be utilized in space-based applications including broadband RF cross-link communications in satellite constellations and the Air Forces V/W-band communications system. Specific examples include the Joint Arial Layered Network (JALN) and AISR architectures. Furthermore, this high-efficiency power MMIC technology can be readily applied to other military/NASA missions in the adjacent frequency bands, V and W. NASA needs high-efficiency, W-band power amplifiers for many of its space-based missions. High-efficiency W-band amplifiers are required for the LO multiplier chain for the Scanning Microwave Limb Sounder on the Global Atmospheric Composition Mission and for SOFIA (Stratospheric Observatory for Infrared Astronomy). The output power levels and efficiencies for these NASA applications are in line with the requirements of this program. Finally, QuinStar is currently supplying the transmitter for the AARGM missile and the W-band high power amplifier technology described in this proposal is directly applicable. QuinStar, as a merchant supplier of high-rel microwave and millimeter-wave components, is uniquely positioned in the marketplace to capitalize on this opportunity to become a major supplier of high-rel, linear, high-efficiency SSPAs for airborne, space and terrestrial applications.