Our solutions are based on automatic data collection from VNA and our Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) routines. You may find more information in the following links for the application note references.

High-Speed Interconnection Characterization using Time Domain Network Analysis
by Roger B. Marks, Donald C. DeGroot, and Jeffrey A. Jargon

Optimizing Time-Domain Network Analysis
by Donald C. DeGroot and Roger B. Marks