For distance transmission at these frequencies, quasi optical systems are usually used. As you rightly point out, TE10 mode waveguide would be completely imprac

For distance transmission at these frequencies, quasi optical systems are usually used. As you rightly point out, TE10 mode waveguide would be completely impractical. See here for a good explanation of quasi optical transmission: https://www.bridge12.com/learn/what-are-quasi-optics/ https://www.bridge12.com/learn/what-are-quasi-optics/