Modular or software-defined instruments have become common in design, validation, and production test systems. With capabilities spanning high-accuracy DC to RF, the need to service these products globally can become a challenge for calibration organizations. Modular instruments operating at RF or microwave frequencies specifically present a unique set of requirements to the world of metrology. Architecturally, engineers build many of these RF modular instruments from multiple individual devices. For example, a vector signal generator (VSG) might be a combination of three separate modules; an I/Q modulator, arbitrary waveform generator, and RF source to serve as the local oscillator. When calibrating this instrument, engineers must consider both the individual module perspectives as well as the assembled system, which in this case makes up the VSG. Furthermore, due to the nature of the instruments and high number of test points verified during calibration, automation is a necessity to meet time and cost requirements. This paper discusses the challenges faced in developing automated module and system calibration procedures for two such RF modular instruments: a 6.6 GHz vector signal analyzer (VSA) and 6.6 GHz VSG.
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