They are rather fascinating. After those guys came forward years ago I had written them off as pranks but I think there might be more to them than a couple of jokers with some wooden planks. I certainly don't think they're of extra-terrestrial origin but definitely man made.

I think a logical explanation is some sort of beam weapon due to the expulsion cavities found in some circles where the plants have been broken from some sort of energy, rather than mechanical action.

This is an interesting read. It mentions an eyewitness account of seeing something suspended in mid air, hidden by cloud cover in an area known for crop circles. Could be BS, could be something. It seems like they would have to operate like a 3D printer head, moving about the "canvas" just blasting directly down rather than staying stationary with a directable beam as there would be overhangs in the designs.

https://boingboing.net/2010/04/28/of-flattened-flora-a.html

This theory leads to a couple of questions. Why create this tech? Well, having some invisible energy weapon blasting down with point point accuracy would be very handy on a modern battlefield. Why test it on land that was public/not military testing ground/top secret? Plausible deniability. If they're testing this stuff in farmers fields, well, anyone can access these and create these designs. If these keep on appearing on military proving grounds, people are going to notice and they wouldn't be able to blame it on a few artists wandering around in the dark for a laugh.