Slipstream Design Successfully Innovates a Modified Three-Level Doherty Amplifier Using NI AWR Software
Founded in 2011 and based in the UK, Slipstream Engineering Design Ltd is a growing design firm with a strong customer base of major original equipment manufacturers who rely on the company’s hands-on and flexible approach. Slipstream Design leads the way in innovative wireless and digital product development for applications including radar. The company’s high-speed, high-frequency designers are passionate about RF and digital technology and specialize in the development and test of sub-systems for the aerospace, communications, and security industries. The main areas of focus lie in RF and microwave design up to 60 GHz, high-speed field-programmable gate array (FPGA) design, and embedded system design.
The Design Challenge
Slipstream Design engineers were responsible for the design of a complex, modified three-level Doherty power amplifier (PA) for use in security-related counter-terrorism equipment. Modern communication systems routinely use complex modulation techniques that result in peak-to-average ratio (PAR) signals of 9 dB and higher. To achieve sufficient linearity, these high PAR levels require a PA to operate far below the power levels that would yield optimum power-added efficiency (PAE). The Slipstream Design PA had large-signal dynamic load-pull effects that had to be carefully modeled prior to fabrication and it was important to balance the PA performance to operate optimally at both high- and low-power levels. The project had a tight design schedule and pressure to deliver a right-the-first-time prototype.
The Slipstream Design team chose NI AWR Design Environment, specifically Microwave Office circuit design software, for its innovative three-stage Doherty PA design due to the software’s superior nonlinear large-signal harmonic balance technology. For the initial design, the team used small-signal S-parameters to obtain an approximate design solution. As the design developed, it was important to understand, in detail, the large-signal performance as it related to terminating load impedance, a key factor in determining Doherty PA operation. Using the large-signal modeling tools in Microwave Office, the team was able to implement the entire RF layout and simulate the full amplifier prior to committing to the printed circuit board (PCB).
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