To improve the accuracy of mixer group-delay measurements, the PNA-X analyzers use a technique known as a vector mixer calibration. Group delay measurements require that the frequencies of the reference and test receivers are precisely the same. Because the two receivers will be used at the input and output of a frequency-translation component, an additional reference or calibration mixer is needed to ensure that the input signal to the reference receiver is the same frequency as the output signal to the measurement receiver.

The PNA-X analyzers are also well suited for amplifier measurements, including low-noise amplifiers (LNAs). Using a noise-figure-measurement approach known as the cold-source method, the analyzers eliminate the need for a noise source at the input of the amplifier under test. The analyzers use vector error correction to compensate for mismatch effects, and overcome noise-parameter-induced errors with the aid of a standard Agilent ECal electronic calibration module, which serves as a variable impedance tuner to vary the source match of the test system or each measurement frequency point. The approach allows the effects of switches, cables, fixtures, or probes to be removed from test results.

Perhaps the most powerful version of the new PNA-X VNAs is with the optional NVNA measurement capability and nonlinear X-parameters for device characterization and modeling (Fig. 2). X-parameters are a mathematical extension of S-parameters, but for nonlinear, large-signal conditions. The vector-corrected parameters can provide insight into a transistor, amplifier or other active device in its linear and nonlinear operating regions. In addition, the X-parameters can be readily extracted into Agilent’s Advanced Design System (ADS). The capability of applying X-parameters to active devices through 50 GHz provides the possibility of developing valid nonlinear models of devices even through their harmonic regions. Agilent has also partnered with companies such as Maury Microwave and their load-pull tuners (Fig. 5) to provide the capability of measuring X-parameters under different load conditions. Agilent Technologies, Electronic Measurement Group, 5301 Stevens Creek Blvd., MS 54LAK, Santa Clara, CA 95052; (877) 424-4536, (408) 345-8886, FAX: (408) 345-8474, Internet: www.agilent.com.