On Mar 20, 11:49*pm, Art Unwin wrote:
*Intuition tells me that when using a perforated plate the lower the
frequency then the smaller the perforations in the shield to create a
blocking effect. ...* The books state for a mesh shield the perforations
should be less than 1/10 of a WL which on the surface opposes
the results obtained by the box experiment! ... Where has my intuition
gone wrong in opposing the books?

If reality will help shape your intuition, then you may be interested
in this paste-up from an IEEE paper linked below.

Note that the spacing of the conductors in the mesh forming these
cavities is much greater than your intuition says is required "to
create a blocking effect."

http://i62.photobucket.com/albums/h8...y_Radiator.gif

RF