Modular measurement systems have gained in respectability and use over the past decade, with most top-level test-and-measurement equipment manufacturers now offering modular versions of different test functions at RF and microwave frequencies. At one time considered lacking in accuracy and repeatability compared to traditional, benchtop instruments, newer instrument modules can typically match the performance of their larger benchtop counterparts, while sliding into a rack-mount mainframe with many other different-function modules.

One of the best known companies in modular instrumentation is National Instruments. At the recent 2013 International Microwave Symposium (IMS) in Seattle, WA, the firm announced that it is working with some of the more specialized companies in high-frequency test, with the intent of providing solutions for source and load-pull measurements.

More specifically, National Instruments is using its test signal and analysis hardware and measurement software in combination with companies that design and supply precision load-pull and source-pull tuners capable of varying the impedance shown to an amplifier under test—among them, Anteverta Microwave, Focus Microwaves, Maury Microwave, and Mesuro, The goal is  to provide practical measurement solutions for source and load pull characterization requirements placed on microwave power amplifiers for aerospace and defense and wireless infrastructure applications.

According to Steve Dudkiewicz, Director of Marketing and Business Development at Maury Microwave, “Modular PXI products such as the NI vector network analyzer simplify the load pull setup by merging all instruments into a convenient low-cost chassis, which improves overall measurement speed and usability.” He adds that “the system guarantees adaptability as new technologies and modulation schemes emerge because we can add PXI modules ad hoc, and users can modify and script custom load pull sequences using an NI open-source load pull toolkit in LabVIEW.”

Even with the space limitations of a modular measurement format such as PXI, National Instruments has managed to squeeze impressive capabilities into its modules. The NI PXIe-5672, for example (Fig. 1), is a 2.7-GHz vector signal generator (VSG) capable of controlling standard or custom waveforms with real-time bandwidths as wide as 20 MHz across a carrier-frequency range of 250 kHz to 2.7 GHz. The compact signal-generator module operates at a sampling rate of 100 MSamples/s with 16-b resolution and can command output levels from -145 to +10 dBm. Each module is shipped with a version of the company’s NI LabVIEW Modulation Tookkit software; this provides extensive tools for signal generation, signal analysis, signal visualization, and processing of waveforms for commercial, industrial, military, and even medical applications.

1. Built in the PXI format, the model NI PXIe-5672 is a 2.7-GHz vector signal generator with carrier-frequency range of 250 kHz to 2.7 GHz. (Photo courtesy of National Instruments.)

With its 3000 Series of RF Modular Instruments, Aeroflex has extended its PXI modular instruments to signal-generation speeds of 6 GHz and signal-analysis rates to 13 GHz. It supports the modules with its PXI Studio application software for signal generation and vector signal analysis, with large libraries of the type of signal formats found in wireless communications systems, including quadrature-amplitude-modulated (QAM) and phase-shift-keying (PSK) signals.

As an example of its PXI signal generators, its 3010/3011 synthesized PXI signal generators cover a frequency range from 1.5 to 3.0 GHz with 1-Hz frequency tuning and 250-μs frequency switching speed (with Option 01). These modules can operate with internal or external frequency references, achieving impressive phase-noise performance of -116 dBc/Hz offset 20 kHz from the carrier at 2 GHz and -140 dBc/Hz offset 1 MHz from the same carrier. The sources can be equipped for in-phase/quadrature (I/Q) modulation. These synthesized sources deliver as much as +3-dBm output power.

Mini-Circuits, perhaps best known for its RF/microwave components, also has designed and developed numerous portable test instruments with the Universal Serial Bus (USB) interface—including switch matrices and signal generators. The firm’s new model SSG-6400HS USB synthesized signal generator is reviewed in detail in this issue (see p. 90). It has a frequency range of 250 kHz to 6400 MHz and an 85-dB dynamic range that can be set in steps as small as 0.01 dB from -75 to +10 dBm.