High-Efficiency, Ka-Band Solid-State Power Amplifier Utilizing GaN Technology

QuinStar Technology proposes to develop a high-efficiency, solid-state power amplifier (SSPA), operating at Ka-band frequencies, for high data rate, long range space communications. Specifically, we propose to develop a 20 W power amplifier with an associated PAE of 60% operating over the 31.5 to 34 GHz band. This will be accomplished by employing two major innovations. First, we plan to utilize wide bandgap Gallium Nitride (GaN) on Silicon Carbide (SiC) device technology to fabricate our high-efficiency MMICs. Operating at a higher voltage (typically 20-28 V versus 4-5 V for GaAs), GaN permits power densities which are 5-10 times higher than GaAs or InP. In addition to a higher power density, high-voltage operation results in lower matching and cell combining losses, making these MMICs more efficient. Secondly, we are proposing to utilize a switching mode of operation (Class-F) to enhance the device efficiency. While this method has demonstrated PAE levels of >80% at 2 GHz, these levels have not yet been realized at Ka-band frequencies. Computer simulations, contained in this proposal, indicate that by using this method, device PAE levels ranging up to 73% are possible at 32 GHz. Furthermore, this was verified by benchmark data from at least one GaN foundry showing a device, operating in Class-F, with a PAE of 80% at 3 GHz. Finally, simulations at Ka-band frequencies indicate that even with circuit losses, we can still maintain the efficiency (PAE) at or very close to 60%. The layout and performance of a multistage MMIC is included in this proposal, together with the overall SSPA configuration and performance.

Future NASA robotic and manned space exploration missions require high-efficiency power amplifiers, operating at Ka-band, for high data rate, long range space communications. Ka-band is the frequency of choice since it 1) provides more available bandwidth for higher data rates and 2) offers a theoretical benefit of 12 dB in EIRP compared with X-band (8.41 GHz) for the same antenna aperture size. Current technology can provide efficiency levels typically in the 20-25% range, and with packaging, combining networks and power conditioning, the efficiency rarely exceeds 15%. Employing GaN device technology together with switching mode (Class-F) device operation, our approach shows the potential to achieve PAE levels of 60%. Since the transmitter SSPA is usually the largest consumer of spacecraft DC power, our high-efficiency approach potentially represents a high-value proposition for NASA. In addition to this telecommunications application, NASA employs active Ka-band sensors (radars) for planetary landings and for a wide variety of Earth science missions, including Ka-band radar for cloud measurements, weather and climate variability studies. Since these sensors are airborne or satellite based, they would also benefit from this high-efficiency SSPA.

Applications for high-efficiency Ka-band amplifiers abound in the commercial segment as well as DoD. These include SATCOM applications for the Army in the 29.5 to 31 GHz band to radar applications for all military services in the radar bands (33 to 38 GHz). For radar, high efficiency is particularly important for airborne applications, such as UAVs and fire control radars, where the prime power is limited. In the commercial segment, a massive market exists for high-efficiency SSPA to replace tubes in SatCom terminals. Additional markets include airborne terminals for commercial airlines using SatCom (27 to 31 GHz), emerging communications applications in the 38-39 GHz range, weather and environmental monitoring radars operating in the 34 to 36 GHz band, aircraft landing systems to enhance or replace Synthetic Vision Systems (SVS) with EVFS at 35 GHz, Security and Surveillance radars for commercial, industrial and municipal applications and helicopter collision avoidance radars for brown-out and obstacle avoidance. Further, this technology is scalable. By using power combining technology, we can provide high-efficiency amplifiers with output power levels well beyond the current goals of this program. For example, with the current 5 W chip and a 16-way combiner, power levels approaching 80 W are readily attainable.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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