Waveguide calibration of VNA using 1/8 and 3/8 wavelength offset shorts.

There are a couple of common ways of calibrating a VNA with waveguide.

Method 1)

• Flush short
• Quarter wave spacer plus the short, to create a 1/4 wavelength offset short
• load

Method 2)

• 1/8 wavelength offset short
• 3/8 wavelength offset short
• load

The 1/8 and 3/8 offset shorts have a quarter wave difference between them, which is electrically the same as the quarter wave spacer achieves.

I'm trying to find a paper which shows any actual benefit of the 1/8 ad 3/8 wavelength offset short. The theoretical advantage is the join between the waveguide and calibration standard occurs at a low current point if using 1/8 and 3/8 offset shorts, but at a high current point if using the flush short or short + 1/4 wave shim.

I believe the work on this was done at an Australian standards laboratory, although I am not sure which one. Most likely it would have been the National Measurement Institute (NMI) in Australia.

Can anyone provide a reference?

Dave