Until now, measuring the nonlinear behavior of RF components was not easy. And there were no scattering or S parameter equivalent for the nonlinear region. While S-parameters were developed as a method to analyze and model the linear behavior of RF devices, they have limitations and are defined only for small-signal linear systems.

To tackle this problem, researchers at Agilent Technologies have developed X parameters. Unlike S-parameters, X-parameters represent and analyze the nonlinear behavior of RF components in a much more robust and complete manner, said Chad Gillease, senior application engineer for Agilent’s Component Test Division, Electronic Measurements Group. As an extension of S-parameters under large-signal operating conditions, they are driven into saturation (the real-world operating environment for many components) and then measured under these conditions, added Gillease. When making this measurement, no knowledge is used or required concerning the internal circuitry of the DUT. Rather, the measurement is a stimulus response model of the voltage waves. In other words, he continued, the absolute amplitude and cross frequency relative phase of the fundamental, and all related harmonics, are accurately measured and represented by X-parameters.

In effect, X-parameters are the mathematically correct extension of S-parameters to large-signal conditions, noted Loren Betts, applications engineer with Agilent’s Component Test Division, Electronic Measurements Group. Like S-parameters, X-parameters are a simplified representation of the full nonlinear spectral map describing device behavior.

Consequently, Agilent has crafted a solution that employs both nonlinear component characterization and X-parameters to provide critical insight, essential to accurately measuring a device’s nonlinear behavior. Toward that goal, the company has developed a nonlinear vector network analyzer (NVNA) software that effectively converts a 4-port PNA-X into a high-performance nonlinear analyzer. Featuring nonlinear component characterization, new nonlinear scattering parameters called X-parameters, and nonlinear pulse envelope domain capabilities, it is aimed at R&D engineers and scientists researching and designing active RF components.

By understanding and being able to control and minimize a device's nonlinear behavior, engineers can create linear high-power solutions. Currently available tools and models for accomplishing this task can be difficult to use and often do not provide the required information, according to Agilent. Unlike others, its new NVNA capability provides a fast and powerful approach to solving this challenge, enabling characterization of a device's nonlinear behavior with the highest level of accuracy, speed and ease-of-use in the industry, noted the developer.

The new NVNA offers the ability to measure the calibrated amplitude and cross-frequency relative phase of measured spectra from 10 MHz to 26.5 GHz. Component characterization is enabled by measuring and displaying both the amplitude and phase of the full spectra -- fundamental, harmonics and cross-frequency products -- in the familiar and powerful PNA-X network analyzer. As a result, engineers are now able to better understand and more deterministically control the nonlinear behavior of their device under test (DUT), asserted Agilent. Data can be displayed in time, frequency, power or user-defined custom domains, providing additional insight into the nonlinear behavior of their components.

Another key feature is its ability to provide nonlinear scattering parameters or X-parameters. Such functionality extends linear scattering parameters into the nonlinear operating region and enables an accurate portrayal of both nonlinear device and cascaded nonlinear device behavior using measurement-based data. The X-parameters can be used in Agilent's Advanced Design System to accurately simulate and design using nonlinear components, module and systems. The result is the highest level of insight into nonlinear DUT behavior, making the NVNA capability especially useful for scientists researching new RF technologies and engineers involved in designing today's high-performance active devices.

The NVNA also provides a nonlinear pulse-envelope domain measurement, which enables researchers to gain a deeper understanding of the memory effects exhibited by their devices by displaying the harmonic pulse envelopes. Both the amplitude and phase of the pulse can be displayed in the time domain, which shows the changes over time.

Nonlinear test set-up using NVNA

According to Agilent, the new NVNA options for the N5242A PNA-X microwave network analyzer are available now. Option pricing starts at $56,000.

www.agilent.com

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