A dverse effects of nonlinear behavior in active and passive high-frequency components can disrupt communications systems. As a result, it is desirable to understand such behavior, which requires the right test equipment. To help, Agilent Technologies (www.agilent.com) has announced nonlinear vector network analyzer (NVNA) capability for its PNA-X series of microwave vector network analyzers (VNAs). Working with new software, the analyzers can perform both nonlinear component characterization and directly measure nonlinear scattering parameters called X-parameters from 10 MHz to 26.5 GHz.
The Agilent NVNA software transforms one of the firm's fourport PNA-X VNA systems into a nonlinear VNA (see figure). The NVNA capability is based on a standard PNA-X microwave network analyzer, which maintains its linear measurement capabilities.
A four-port PNA-X with NVNA capability measures all of the input and output spectra for a device under test (DUT), including fundamental input and output signals, harmonics, and cross-frequency products generated by the DUT's intermodulation distortion (IMD). The analyzer can display all amplitudes and phases of these products, along with the relative amplitude and phase of any frequencies of interest. Such information can be used to develop a matching circuit and/ or filter to minimize unwanted distortion from a power amplifier (PA). The test data can be shown in frequency, time, or power domains, as well as in terms of user-defined ratios. For example, if a DUT's output is distorted in the time domain, a user can switch to the frequency domain to identify the amplitude and phase of individual frequency components. Input test power can be varied to study the sensitivity of a DUT to different power levels.
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. The pulse amplitude and phase can be displayed in the time domain, showing changes as a function of time.
The NVNA measures X-parameters to better understand a DUT under saturated signal conditions. In contrast to the four standard S-parameters, the number of X-parameters for a given measurement can be much higher, since X-parameters represent a DUT's crossfrequency dependencies under nonlinear conditions. One X-parameter might be the gain of the output fundamental frequency as a function of the input third-harmonic frequency. Because of the synergy of Agilent's test and computer-aided-engineering (CAE) tools, the X-parameters measured with the NVNA system can be used in Agilent's Advanced Design System to accurately simulate and design using nonlinear components, module and systems. P&A: $56,000 and up (Agilent N5242A PNA-X with NVNA options); stock. Agilent Technologies, Electronic Measurements Group, 5301 Stevens Creek Blvd., MS 54LAK, Santa Clara, CA 95052; Internet: www.agilent.com.