UPEND Power Amplifier Project
UAS Power amplifier for Extended range of Non-payload communication Devices (UPEND)
NASA SBIR Phase I & Phase II Project
The integration of Unmanned Aircraft Systems (UAS) into the National Airspace System (NAS) requires a robust and reliable Control and Non-Payload Communication (CNPC) system between the Unmanned Aerial Vehicle (UAV) and its operators. Simply put, constant communication is a necessity. One method to improve link uptime and extend link distance is to insert a Radio Frequency (RF) Power Amplifier (PA) into the communication system. However, current PAs fall short of delivering the necessary linear RF power and DC power efficiency in a package small enough for UAVs between 21 and 55 pounds in weight, known as Group II, which include the Insitu ScanEagle.
Significance of the Innovation
NuWaves Engineering and its partners have been researching, designing, and developing a high-efficiency, high-linearity C-band power amplifier based on a custom Monolithic Microwave Integrated Circuit (MMIC) design using Gallium Nitride (GaN) material. This MMIC technology features state-of-the-art analog predistortion linearization and a Doherty power amplifier topology enabling very efficient operation, especially for amplitude-modulated waveforms such as 802.11, 802.16, LTE, etc.
As part of the scope of the UPEND project, NuWaves is designing the power amplifier circuitry, including biasing, monitoring, and power supply circuitry, as well as a connectorized mechanical enclosure suitable for aircraft integration.
NuWaves Engineering had been developing high-efficiency Power Amplifier modules for nearly a decade and was awarded this Phase I SBIR from NASA in 2014. During the Phase I effort, a model was designed and simulated, achieving significant improvement in Error Vector Magnitude (EVM) and power efficiency over the current state-of-the-art in commercially available PA devices. Additionally, a proof-of-concept prototype was fabricated and tested that validated the model with respect to EVM performance improvement with linearization.
As a result of this Phase I research, NASA awarded NuWaves a Phase II SBIR in 2015. In the Phase II effort, NuWaves is addressing the amplifier needs of two different types of communication data links: those with amplitude-modulated waveforms (e.g. OFDM) and those with constant-envelope waveforms (e.g. PSK). Therefore, two unique GaN die — a high-efficiency power amplifier and a linearizer – have been fabricated, wire bonded, and packaged into surface-mount integrated circuit (IC) components.
Anticipated PA Module Performance
The table below provides the anticipated PA module performance with and without the linearizer MMIC.
1Taken with EVM of -28 dB (4%)
2Taken at Saturated Output Power
The plots below show the simulated Power Added Efficiency (PAE), Pout (dBm), and Error Vector Magnitude (EVM) as a function of Pin (dBm) for the prototype Doherty amplifier as well as for the linearizer and Doherty amplifier circuit at 5.05 GHz with a 10 MHz OFDM waveform. In both cases greater than 40% PAE is achieved with greater than 10 dB of input power back-off. The addition of the linearizer shows minimal change to PAE and output power curves, but improves the EVM for much of the power sweep. As referenced by the dashed horizontal marker, the addition of the linearizer allows the amplifier to provide more than 10 dB of additional output power and operate at 25% greater efficiency at the same linearity level in terms of EVM.
Simulation of prototype Doherty Amplifier circuit (left) and linearizer and Doherty Amplifier circuit (right) at 5.05 GHz under a swept input average power with a 10 MHz OFDM waveform.
(Phase I & II)
Future Work (Post Phase II)
Planned post-Phase II efforts include productization of the packaged MMIC PA ICs and connectorized PA modules. The former will allow OEMs to integrate these devices inside their data link transmitter and transceiver designs. The latter will allow for module-level integration of these devices into UAVs.
Additionally, the technology is scalable to different frequency bands (e.g., S-band, Ku-band, etc.) and power levels opening up this technology to additional markets and applications.
NuWaves is actively seeking post-Phase II commercialization partners for potential post-Phase II collaborative funding with the NASA SBIR Program.