Linearization of HF Power Amplifiers using Direct Digital Predistortion at RF

Nonlinearity of RF Power Ampifiers (PAs) produces harmonic and intermodulation distortion of communication signals, significantly limiting overall system performance. This is a particular problem for multi-carrier signals in a very broadband channel, especially those spanning multiple octaves, such as HF (2-30 MHz). Conventional approaches to deal with this problem are intrinsically narrow-band and of limited effectiveness. Based on our Phase I analysis, HYPRES proposes to demonstrate a unique digital-RF approach - true RF predistortion in the digital domain. In this approach, a broadband, multi-carrier RF signal is digitized directly, and predistorted in real-time using high-speed digital electronics. This will produce performance enhancements well beyond those achievable by conventional approaches. First, hardware prototype test-bed will be developed using commercial silicon-based technologies, including a high-speed ADC, RAM, and DAC. In parallel, HYPRES will implement the same predistortion techniques using ultrafast superconducting electronics, which can be extended in the future into the multi-GHz range (well beyond the capabilities of commercial silicon), for application to other RF bands. This will extend HYPRES' projects in digital-RF receiver components, to a full set of digital-RF transceiver products for military and commercial markets.