On Thu, 7 Feb 2008 10:10:30 -0800 (PST), wrote:

Lets be silly. Take a commercial yagi TV aerial, take a strip of
cardboard, and make a full size copy of the layout using bits of 2.5mm
T&E cable for the elements, and the cardboard to replace the spine.

How well would it work?

Perfectly well on the single frequency it was designed for. The
diameter of the elements affects the range of frequencies the antenna
will remain effective on so its bandwidth would be less than the
commercial equivalent as the wire is thinner than the aluminium tube.