How does this horn/waveguide work?

From https://audiohorn.net/tweeter-waveguide/

1751036702863.png

It looks like a normal phase plug we see in smaller 1 inch voice coil compression drivers with 1 inch throat.
A cloth/silk dome tweeter works in breaks up mode, how can a horn/waveguide produce a plane wave?
Can somebody please explain what is happening? @Patrick Bateman

Thanks and Regards,
WonderfulAudio
 
Last edited: