Hi, The attenuation resulting from puting a signal into a parallel plate waveguide is dependent on the excited mode. Why does the TM mode have greater attenuation than the TE mode? I can see in the maths it 'works out' to be that, but what would be a more conceptual/physical reason? Is the TM mode in contact with the boundary more than the TE mode This image seems to indicate that there is more electric field touching the conductor in TM polarisation, so my guess is that this would cause the greater conductor loss (because there would be a larger evanescent field in that would be lost in the conductor). loss.png shows the attenuation curves for various modes (the image is from the textbook by Pozart). Thanks.