waveguide beyond cut off

[greebling]

Consider a pipe of diameter 1.25 lambda and length 10 lambda. At far end of pipe is a larger chamber. At entrance of pipe is a cylindrical blockage approx lambda diameter and lambda long. Will the blockage be sufficient to prevent RF from propogating down the pipe into the larger chamber?

 

[TWW]

The lowest mode of propagation is TE01 with a cutoff of 1.64*diameter therefor your waveguide is cut off. 1/4 wavelength of cut-off waveguide is enough to extinct all of the evinescent energy.