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

QuinStar Technology proposes to develop an efficient, 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. 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 the 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 (Class F) to enhance the device efficiency. While this method has demonstrated PAE levels of >80% at 2 GHz, it has not yet been demonstrated at Ka-band. Computer simulations, contained in this proposal, indicate that by using this method, PAE levels ranging from 65% to 80% are possible. This was verified by device models from three different foundries. Finally, we will utilize our high-efficiency, H-tee combiner technology to combine 4 of these chips to achieve 20 W output power.

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 16 (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 potential to achieve PAE levels of 60%. Since the transmitter SSPA is usually the largest consumer of spacecraft power, our high-efficiency approach represents a high-value proposition for NASA. In addition to this telecommunications application, NASA employs active (radar) Ka-band sensors for a wide variety of Earth science applications, 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 SSPAs 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 of 80 W are readily attainable.

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