Penang writes:

What's your suggestion / opinion on how to construct an excellent
(pair) of MIMO antenna for wifi (802.11 b/g/n) ?

Not MIMO, but many weird looking, but mostly sound, ideas he

http://usbwifi.orconhosting.net.nz/

"Make 2.4GHz parabolic mesh dishes from cheap but sturdy Chinese
cookware scoops & a USB WiFi adaptor"

By placing the wi-fi adaptor in the antenna, you don't lose radio power in
cables and connectors. You have to be careful about waterproofing,
though.

Jon