ridged pyramidal horn antenna (rectangular), effect of freznel lens

[CopperCone]

I don't mean a lens horn (the conical shape one), but a regular pyramidal horn that has a lens on it. The lens I speak of looks like a ziggaraut made of concentric ovals, with the spacing between the elevation planes approximately 1cm and a depth of 1.5cm over the area of the horn apature.

How much of an effect does it have? Does anyone have pictures of radiation patterns differences because of lens being placed in front of the horn?