I found a reference for calculating cascade VSWRS
using a linear combination method refer to web site
for equation

http://www.y1pwe.co.uk. I don't know how much
this differs from the one you provided.

I
would like to refer to a text reference on this
subject and how does this equation differ for when
you have two components and the worst VSWR is the
multiplication of each VSWR individual VSWR.

Thanks.