Found another pic that you might find of more use.
The grille had a plastic mesh behind it to begin with but this got cracked so i replaced it with some aluminium punched plate painted black...then just a few weeks latter a pheasant flew up and cracked the grille. I might get round to repairing it some day with some filler and fibreglass. http://www.dhendry.plus.com/images/zx/DCP_0688.JPG