Thin Slotted Waveguide for 2.4Ghz

As I maybe mentioned in my previous post hlssa program gives some very strange results about thickness dimensions of the waveguides. The program says that is passable to build slotted waveguide whit an only 100mm to 25mm tube or waveguide for 2.4ghz band.
Till now I was unable to find anything that confirm this, but now I sow several interesting pictures :






Pictures are from here : www.starhill.org
Look at this - there is NO WAY that this is be 100×50 mm this looks like more like 20 or 25mm !!!
So this will make passable to use other, more easy to be found on the market tubes.
More pictures :
And finally one more thing - 20 to 22dbi omni directional slotted waveguide 25mm thin PDF file whit specification