RF VNA Calibration Kits are essential test and measurement hardware for nearly all types of VNA measurements. Though VNAs come with internal calibration from the manufacturers, there are a variety of environmental and temporal factors that could lead to significant measurement errors to take into account. This is the purpose of VNA Calibration Kits, of which, the most common type is the short, open, load, and thru (SOLT) calibration kit.
A VNA calibration kit is a set of VNA calibration standards that should be traceable to measurement standards, such as the US National Institute of Standards and Technology (NIST) standards. The calibration standards for VNAs are generally coaxial interconnect standards for a short, open, load, and through (VNA Short Open Load Thru (SOLT) Calibration Kits). Traditionally, these kits come with two shorts, two opens, two loads the same as the characteristic impedance of the transmission lines in the system, and a through (thru) standards. The most common coaxial VNA calibration kits are either 50 Ohm or 75 ohm, though there are others impedances.
It is common enough for a VNA calibration kit to also come with some precision adapters to common coaxial interconnect types. A VNA calibration kit is typically chosen to match the VNA test ports, or to match a frequently used coaxial connector type based on the devices-under-test (DUT) or what happens to be available in the test lab.
There are also VNA calibration standards that come in a combined format, such as 3-in-1 Short Open Load (SOL) Calibration Standard. These calibration standard units come with at least a short, open, and load port and are generally purchased in pairs. There are some calibration standard combined units that come with a through as well, but a precision inline adapter often provides this same function without the need to include it in a calibration standard.
RF VNA Calibration Kits also often include precision wrenches and torque wrenches specifically designed for use with VNA Calibration Kits. The wrench sizes and torque are specifically paired with the coaxial connector standard and the recommended torque specified for the coaxial connector type. In some cases, a calibration standard may be damaged or misplaced over time. In this case, individual 50 Ohm VNA Short Open Load Thru (SOLT) Calibration Components or 75 Ohm VNA Short Open Load Thru (SOLT) Calibration Components are often sold piecemeal instead of in a complete kit. This is a much more affordable approach if only one or two standards are needed instead of an entire kit.