All our coaxial calibration kits can be used with the VNWA from SDR-kits. In fact Kirkby Microwave own a VNWA, in addition to several higher end VNAs. The VNWA supports three calibration models:

- Ideal calibration standards. These just assume simple theoretical text-book standards, and are not suitable for use with any professional VNA calibration kit.
- Simple model custom calibration standards. These allows delays of standards to be entered, but not the fringing capacitance, so again is not suitable for use with professional calibration kits.
- Arbitrary model custom calibration standards.
**The arbitrary model should be selected**to use Kirkby Microwave calibration kits, as the other models are too simplistic. See the image below.

This model is very flexible, but is not as easy to use as other VNAs. The calibration standards are represented as a mathematical model, which can be expressed as either S-parameters (S), an admittance (Y) or as an impedance (Z).

For the load use the impedance, and enter a value of 50. Our loads are characterized for a low reflection coefficient from DC up the maximum
frequency of the calibration kit. Do **not** use the DC resistance, as SDR-kits suggest. Despite having a calibrated HP 3457A 6.5 digit multimeter,
with support for 4-wire resistance measurements, we do not measure the DC resistance, and suggest this is not done, even if you have a suitable
bench multimeter. This is because the DC resistance tells you nothing about how the device acts at RF frequencies.
Set either **S=0** or
**Z=50** for the load. Just set the delay to 0, as that's irrelevant. Press carriage return to compile the data entered.

Set either **Z=0** or **S=-1** for the short. Set the delay to the NEGATIVE value of the of the standard
in the Kirkby Microwave kit. Typical values that would need setting would be from -75 ps to 0 ps, depending on the model of kit,
and the gender of the calibration standard.

The open standard is the most complicated to define. It is possible to compute the S-parameters, impedance or admittance of the open standard, but using the admittance is easiest. The open standard has a fringing capacitance C, which is frequency dependent. The admittance of a capacitor is:

Y=j*ωC where j=sqrt(-1) and ω = 2*πf

The fringing capacitance of the open calibration standards follows the method used by almost all VNA manufacturers - a 3^{rd} order polynomial.

C_{fringing}=C0x10^{-15} + C1x10^{-27}f + C2x10^{-36}f^{2}+C3x10^{-45}f^{3} farads, where f is in Hz.

If a kit had an offset delay of 50 ps, and the fringing coefficients were C0=60, C1=70, C2=80 and C3=90, the admittance would be written in the VNWA as below, where the VNWA uses w instead of ω

Y=j*w*(60e-15 + f*70e-27 + f*f*80e-36 + f*f*f*90e-45)

Kirkby Microwave Ltd is registered in England and Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT.