RF Calibration Kit, Number of Mating Cycles and Proper Maintenance

Calibration is an essential step in any RF test and measurement procedure. By calibrating our measurement setup with known standards, we can reduce measurement uncertainty. For millimeterwave testing, SAGE Millimeter provides calibration kits that include precision machined shorts, open and loads accompanied by a set of in-series adapters with their respective connector type, see Fig 1. 

Table 1: SAGE Millimeter Coaxial Calibration Kits

Table 1: SAGE Millimeter Coaxial Calibration Kits

ModelFrequency RangeConnector Type
STQ-TO-3F3M-U3-CKIT1DC to 26.5 GHz3.5 mm
STQ-TO-KFKM-U3-CKIT1 DC to 40 GHz 2.92 mm
STQ-TO-2F2M-U3-CKIT1 DC to 50 GHz 2.4 mm
STQ-TO-VFVM-U3-CKIT1 DC to 67 GHz 1.85 mm

A common question is “How many mating cycles can each calibration component support over its life?” The standard answer for SAGE Millimeter’s coaxial calibration kits is 500 matings. The reality is a bit more complex and nuanced. As with any type of connector, there is a life cycle associated with it and some performance degradation with each connection. Proper handling and maintenance of the calibration kits along with the adoption of strict rules for usage and storage can help preserve and extend the life of the calibration kit. Likewise, improper handling can ruin a calibration kit in just a couple of incorrect connections [1]

Cleanliness is… A Must!

With any precision measurement set-up, inspection and maintenance is a key step that is often overlooked. It is important to inspect all calibration standards and mating connectors before every use. Often, burrs or nicks that develop from improper mating on a male connector can seriously damage any subsequent female connector and vice versa.

Dirt, grease and oil from our fingers and the environment can change a calibration standard’s impedance [2]. (Do you keep dropping that short on the floor? Pro-tip: Close the gap between you and the workbench using your chest.) The outer and inner surface of the connectors and calibration standards can be cleaned using isopropyl alcohol and a clean lint-free cloth. Often, a blast of compressed air can dislodge dirt or unwanted particles [3]. Don’t forget to periodically clean instrument connectors as well!

Making a Connection

Once our coaxial standard and instrumentation connectors are clean, it is time to make a connection. Be mindful when connecting any RF connector to an instrument or cable. Take care in the alignment of the connectors and be sure to turn the (male) connector’s nut only. Do not twist the connector body or cable. Failure to do so could easily damage the contact area and even the threading. If the connector is not tightening smoothly, back off and try again, do not force the connection. 

Be careful not to over-tighten the connections. In a lab setting, SAGE Millimeter recommends finger-tight around 6 to 10 inch-pounds. When using a torque wrench, the recommended proper torque is 8.0 ± 0.15 inch-pounds (0.90 ± 0.02 Nm). SAGE Millimeter torque wrench, model SCH-08008-S1 or STQ-CH-08008-U2 (provided with our calibration kits) is highly recommended.

Finally, after testing, take care to place each coaxial standard and adapter back into the calibration case for proper storage between uses. 

References:

  1. How to (not) Trash a Calibration Kit! Retrieved from https://www.microwaves101.com/encyclopedias/how-to-not-trash-a-calibration-kit
  2. Coaxial Systems: Principles of microwave connector care (for higher reliability and better measurements). (1986, July 1). Retrieved from http://www.hparchive.com/Application_Notes/HP-AN-326.pdf
  3. Rowe, Martin. (2000, May 01). Take Good Care of your RF Calibration Kits. Retrieved from https://www.edn.com/electronics-news/4379681/Take-Good-Care-of-Your-RF-Calibration-Kits

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