Focus microwaves has a large collection of app notes about VNA calibration, load-pull measurements,
programmable tuners, and more. Most of these documents require that you login first, so I cannot
provide direct links to them.
from Cascade Microtech...
Cascade also has quite a lot of app notes and Frequently Asked Questions.
Someday I will get them listed here, but for now, you can browse through
them at these links: