Ka-Band Efficient, Linear Power Amplifiers for SATCOM Ground Terminals

ABSTRACT:QuinStar Technology proposes to develop a high-efficiency, linear, solid-state power amplifier (SSPA), operating at Ka-band frequencies, for low-cost ground terminals. The key performance goals are an output power of 70 W with an associated PAE of 35%, while operating with complex modulation. These goals will be achieved by employing three major innovations. First, we are employing state-of-the-art wide bandgap GaN (Gallium Nitride) devices. These GaN devices have demonstrated power densities of 5 to 8 times higher than competing technologies, GaAs or InP devices. Further, we are proposing to operate these devices in a switching mode (Class F). Simulations presented in this proposal indicate that by using this approach, drain efficiencies approaching 70% are possible. Secondly, we are proposing to utilize a low loss, H-tee combining approach to combine 4 of these high-efficiency chips to achieve 70 watts. Finally, we plan to utilize envelope tracking (ET) to maintain the amplifier in saturation, operating at highest efficiency, and then use Digital Pre-Distortion (DPD) to linearize the resulting amplifier characteristics. Simulations described in this proposal indicate that with this innovative approach, we can simultaneously achieve the output power, linearity and efficiency goals of this program.BENEFIT:High-efficiency, linear power amplifiers are required for Wideband Global SATCOM (WGS) ground based terminals and for AF airborne terminals. Linearity is required in order to prevent spectral regrowth, i.e., extraneous power from one channel interfering with signals in adjacent channels, and high efficiency is required to minimize both power consumption and self-heating, which in turn causes thermal stress. Currently available Ka-band solid-state amplifiers simply do not have the combination of output power, efficiency and linearity required for this application. The efficiency SOA for Ka-band MMICs is in the range of 25%. With practical packaged amplifiers, including matching and combining networks, the amplifier efficiency rarely exceeds 15%, and is even less when operated as a linear amplifier. Employing an innovative switching-mode amplifier concept in conjunction with Envelop Tracking (ET) and DPD linearization, our approach produces a SOA high-efficiency, linear power amplifier. Military applications for high-efficiency, linear amplifier technology include SATCOM applications for the Army in the 29.5 to 31 GHz band, and radar applications for all the military services in the Ka radar bands. There is also a need to replace aging SATCOM satellites such as MILSTAR, with broader ground coverage and increased data throughout. Once again, the same set of amplifier requirements exists higher output power and higher efficiency at Ka-band frequencies. Potential commercial and industrial applications for this technology are summarized below: Ka-band satellite communications. Ground terminal manufacturers are utilizing SSPAs to replace tubes in the 27 to 31 GHz frequency range, with power levels ranging from 10 W to over 1000 W. This market has experienced explosive growth in the last few years with the exploitation of Ka-band for satellite-based broadband communication. The PA (tube and SSPA) market size of this segment is estimated to be $100M/yr with over a dozen major suppliers of tubes and SSPAs. Airborne terminals for Broadband Access in commercial airliners using SARCOM (27 to 31 GHz). This is a new market which is just now evolving. The estimated market size is 10M/yr. and growing rapidly. Ka-band Deep Space communications for NASA at 31.8-32.3 GHz for downlink and 34.2-34.7 GHz for uplink Emerging Ka-band communications applications in new frequency bands. For example, 38-39 GHz for ESAs Alphasat program Weather and environmental monitoring radars operating in the 34 to 36 GHz band. There are airborne and ground-based applications. Potential customers include commercial instrument makers, avionics, etc. NASA 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 technology. Emerging aircraft landing systems to enhance or replace Synthetic Vision Systems (SVS) with EVFS. Imaging and mapping. Frequency: 35 GHz. SSPAs are a superior option to tubes. Security and Surveillance radars for commercial, industrial and municipal applications. These modern radar-based sensors present much higher resolution and ranging than other sensors. Helicopter collision avoidance radars for brown-out and obstacle avoidance.