Hello, i want to construct a pin fed horn antenna,for this i need a coaxial to circular waveguide adapter.
from the article shown bellew we have three parameters:
guided wavelength
cutoff wavelength
free space wavelength.
I cant imagine these types of wavelength
is there some example i could use so i could see from where to take these parameters?
Thanks.

 

This is waveguides 101. How you learn it is up to you, but I'd suggest you find some good lectures from some university site that suit your learning style and work through them. Probably start with rectangular guides as the maths is easier, but as I said - find something that suits you - there's plenty out there.

Here's a general treatment that looks OK: https://www.wtamu.edu/~cbaird/BLecture5.pdf