Column Control DTX

Going Beyond S-parameters with an Advanced Architecture for VNA

Article Reprints

In both R&D and manufacturing, engineers face a number of significant challenges when testing radio frequency (RF) components. In R&D, solving design challenges faster and with fewer design iterations is paramount. Manufacturing demands ever-lower test times and test costs, while maintaining accuracy and maximizing yield.

One way to ease the pressure is with a flexible, highly integrated measurement solution such as the Keysight Technologies, Inc.N5242A PNA-X microwave network analyzer. With its advanced architecture, the PNA-X not only delivers excellent performance and accuracy, but it also can be configured for a variety of measurements beyond the traditional scattering parameters (S-parame­ters) associated with network analyzers. Built-in elements such as a second signal source and frequency combiner enable accurate, informative characterization of nonlinear behavior in RF and microwave devices, particularly amplifiers, mixers and frequency converters.

Ensuring accurate system simulation

Accurate magnitude and phase measurements are crucial to modern wireless and aerospace/defense systems. During the design phase, system simulations need highly accurate component characterizations to ensure that the system will meet its performance requirements. In manufacturing, accurate measurements verify that each component meets its published specifications.

S-parameters are the most widely used measurements of RF components — filters, amplifiers, mixers, antennas, isolators and transmission lines. These measurements characterize the complex-valued (magnitude and phase) reflection and transmission performance of RF devices in the forward and reverse directions. They also fully describe the linear behavior of RF components, which is necessary, but not sufficient, for full-system simulation. Deviations such as non-flat amplitude response versus frequency or non-constant-slope phase response versus frequency can cause serious system degradation.

System impairments also result from the nonlinear performance of some RF components. For example, amplifiers exhibit gain compression, amplitude-modula­tion-to-phase-modulation (AM-to-PM) conversion and intermodulation distortion (IMD) if driven at power levels that exceed their linear range.

Outlining the core measurements

The most commonly used instrument to characterize RF components is the vector network analyzer (VNA). A traditional VNA contains a single RF signal generator that provides a stimulus for the device under test (DUT) and multiple measurement receivers to measure incident, reflected and transmitted signals in both the forward and reverse directions (Figure 1). The source sweeps in frequency at a fixed power level to measure S-parameters and sweeps its power level at a fixed frequency to measure amplifier-gain compression and AM-to-PM conversion. These measurements characterize linear and simple nonlinear device performance.

For basic S-parameters and compression testing, the source and receivers are tuned to the same frequencies. By offsetting the source and receiver frequencies, how­ever, amplifier harmonics can be measured by tuning the receivers to integer multiples of the stimulus frequency. The ability to offset the source and receiver frequencies also enables measurements of magnitude, phase and group-delay performance of frequency-translating devices such as mixers and frequency converters.

While these measurements are typically done with a continuous-wave (CW) stimulus, many devices require testing with a pulsed-RF stimulus, which means the test signal must be gated on and off with a specific pulse width and repetition rate.

Traditional VNAs have two test ports, which was sufficient when most RF devices had only one or two ports. With the rapid rise of wireless communication, three- and four-port devices have become commonplace, and as a result, two- and four-port network analyzers are equally prevalent.

Simplifying amplifier and mixer measurements

Available with two or four ports, the PNA-X features four major improvements to the traditional VNA architecture:

Two sources: Frequency and power level settings for the second internal source are independent from those of the main source. The second source can be used for nonlinear amplifier tests such as intermodu­lation distortion (IMD) or as a fast, local oscillator (LO) signal for testing mixers and converters.

Signal combiner: The internal signal combiner can sum the two sources prior to the associated test-port coupler of the instrument. This simplifies the setup of amplifier tests that require two signal sources.

Switching and access points: Additional switches and RF access points enable flexible signal routing and the addition of external signal-conditioning hardware (e.g., a booster amplifier) or external test equipment (e.g., a digital signal generator or vector signal analyzer).

Pulse capabilities: Internal pulse modulators and pulse generators provide a fully integrated pulsed S-parameter solution.

These improvements simplify test setups and improve test times when measuring amplifiers, mixers and converters. They also work together to expand the range of measurements that can be made with a single set of connections to the DUT. Figure 2 shows an example of simultaneous measurements of S-parameters, gain and phase compression and fixed-signal IMD on an amplifier.

Enhancements in both sources also simplify amplifier and mixer measurements. For example, the maximum signal power available at the test ports is typically +13 to +20 dBm (depending on model and frequency). This is very useful for driving amplifiers into their nonlinear region and is often required when using a source as an LO signal for testing mixers. The sources also contain low harmonics (typically –60 dB or better), which improves harmonic and IMD measurement accuracy. Also, a power sweep range of typically 40 dB makes it easier to characterize an amplifier’s transition from linear to nonlinear operation.

×

Please have a salesperson contact me.

*Indicates required field

Preferred method of communication? *Required Field
Preferred method of communication? Change email?
Preferred method of communication?

By clicking the button, you are providing Keysight with your personal data. See the Keysight Privacy Statement for information on how we use this data.

Thank you.

A sales representative will contact you soon.

Column Control DTX