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Precise calibration of test equipment is one of the most important requirements for reliable testing of RF devices. In this article, we explain why you can rely on your RF results when using SPINNER calibration kits.
The scattering parameters of a device under test (DUT) are measured using a vector network analyzer (VNA). Before starting, however, the VNA should be calibrated applying a set of known calibration standards to identify and minimize systemic errors. Accurate calibration is a must for reliable results. The quality of calibration depends on various factors. They include the test setup, laboratory practices, mechanical quality, and last but not least the electrical modeling approach underlying the calibration standards applied by a kit.
SPINNER calibration kits
SPINNER supplies top-quality calibration kits with OPEN, SHORT, LOAD and THROUGH lines for performing top-quality measurements in labs, on production lines, and on site at customers.
OPEN-SHORT-LOAD (OSL) calibration kits are used for single-port testing and OPEN-SHORT-LOAD-THROUGH (OSLT) kits are used for testing devices with two or more ports. All SPINNER calibration kits are mechanically highly robust and optimized for high repeatability of connections. They include calibration data for various accuracy levels of the electrical modeling.
SPINNER applies the strictest standards of laboratory practice based on ISO 17025 (General Requirements for the Competence of Testing and Calibration Laboratories). Mechanically reliable calibration kits with outstanding connector repeatability and all levels of calibration data are available.
Connector repeatability of a SPINNER short male 1.85 mm for angular positions 0°, 120° and 240°. Repeatability is better than -48 dB for frequencies up to 67 GHz. SPINNER calibration kits let you perform measurements with maximum accuracy and reliability. They are available for numerous connector types including 7-16, N, 4.3-10, NEX10, 2.2-5, 3.5 mm, 2.92 mm, 2.4 mm, 1.85 mm, and 1.35 mm and as a practical 3-in-1 OSL or 4-in-1 OSLT compact kit, and include an array of boxed individual calibration standards.
Electrical modeling of a calibrating kit’s calibration standards can be performed to various levels of accuracy. The standard level is based on a polynomial model for OPEN and SHORT that approximates the scattering parameters of the standards. In addition, the LOAD is assumed to be ideally matched, and the THROUGH is defined by its electrical length. This polynomial model can be "global" – in other words, every OPEN and every SHORT of a particular design share the same model across the product series – or it can be "differentiated" with a different polynomial assigned to each OPEN and SHORT.
The intermediate level uses the measured scattering parameters of each calibration element and is referred to as data-based. The highest level of calibration is achieved with a calibration kit that applies scattering parameters and the associated measurement uncertainties. The International Vocabulary of Metrology (VIM) defines “measurement uncertainty” as “a parameter characterizing the dispersion of the quantity values being attributed to a measurand, based on the information used.”
When working with a uniquely characterized calibration kit, special polynomial model, or scattering parameters, great care must be taken with the calibration data, which only apply to a particular calibration kit of a certain type and unique serial number. The calibration data can change after a recalibration and must therefore be updated on the VNAs used. These kits are therefore mainly used in laboratory applications that call for the highest level of accuracy.
In contrast to the above, kits based on a global polynomial model – like the compact 3-in-1 and 4-in-1 kits available from SPINNER – are very easy to use. The calibration data only have to be entered in a VNA once, and there is no need to change them after it has been recalibrated or replaced with a new kit of the same type. The best solution for ensuring simple, convenient use combines all of the calibration standards in a single handy housing. Its low weight, small size, and ergonomic configuration make it ideal for use at construction sites and in production environments.
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