Overview

High-power RF amplifiers are used in telecommunications, biomedical, and military systems. With output power levels ranging up to 1 kW, these amplifiers are typically designed to operate near or into compression in order to provide the maximum output power possible. This may result in the generation of harmonics, intermodulation distortion, and gain compression which are often undesirable byproducts. As a result, designing high-power amplifiers requires a detailed analysis on its nonlinear behavior.

Problem

In the past, when designing systems with high-power amplifiers, the designer would measure the S-parameters of the amplifier using a vector network analyzer (VNA), load the results into an RF simulator, add other measured or modeled circuit elements, and then run a simulation to predict system performance such as gain and loading effects. Since S-parameters assume that all elements in the system are linear, this approach does not work well for characterizing the nonlinear behavior of devices such as high-power amplifiers. The errors are particularly apparent if we measure the S-parameters of two devices that exhibit nonlinear behavior, simulate the cascade of those devices, and then compare the result to an actual measurement of the two cascaded devices. Simply stated, if an amplifier’s nonlinear behavior is measured using a linear assumption, then the result of the simulation will be wrong.

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While engineers may live with this inaccuracy, it invariably results in extensive and costly empirical-based iterations of the design, adding substantial time and cost to the design and verification process.

Solution

Testing today’s high-power devices demands an alternate solution—one that quickly and accurately characterizes the device’s nonlinear behavior and that is capable of dealing with its high power level. The Agilent nonlinear vector network analyzer (NVNA) and X-parameters* are the solution. Gain in-depth knowledge of testing high-power amplifiers with Agilent’s new high-power white paper. This 30-page paper discusses the unique challenges and solutions involved in characterizing high-power devices using Agilent’s NVNA and X-parameters.