George Craven was one of the pioneers
of evanescent mode filters and other circuit elements
realized in waveguide below cut-off. He therefore
has left a legacy of very many papers and books
on the topic, if you search on the IN for his name
I am sure you will turn up a lot of data.
this, for example:
It discusses the equivalent circuit of the interface
to an inductive section of evanescent waveguide.