Effect of impurities in a waveguide?

Dear all,

Please let me know what effect impurities have in signal transmission through a wave guide.As far as i know that waveguides are made of purest form of copper.Hence if impurities are added to it what effect will it have in signal transmission?Secondly, what other factors effect transmission (other then impurities)?
Any related papers if possible please upload it for me.

Regards,

Rahul

Copper being a conductor will have effect in a waveguide. It will probably effect the impedance and thus, S11, S12 ...

It depends on how much of impurities, how are they position and shaped.

I would recommend the book by T.Moreno: Microwave Transmission design Data, , Dover, N.Y. 1948
There are several chapters devoted to waveguide loss due to materials, surface roughness and dielectric filling.
In general, a practical test is the best way to know. Years ago I was surprised how good a rusty steel pipe can be as an X-band waveguide.