All our coaxial calibration kits can be used with the VNWA from SDR-kits. In fact Kirkby Microwave own a VNWA, in addtion 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.
**This is the model that should be chosen 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 characterised 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. Despiting 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 dependant. 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 insted of ω

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