Techniques for Attenuating a 5GHz Signal Between?
If you stick some ECCOSORB in front of the antennas, it should attenuate the transmitted power pretty considerably.

Basically, you want some sort of microwave absorbing attenuator. There's a number of brands, but it's generally colloquially called "echosorb" or something like that. In general, it's a carbon-loaded open-celled foam substance, which attenuates broadband microwave energy.

The downside is it's pretty specialized, and kind of expensive.


http://www.panashield.com/emc_absorbers.asp
http://www.eccosorb.com/
http://www.ets-lindgren.com/RFAbsorbers
http://www.westernrubber.com/products/himag-microwave-absorbers/himag-reticulated-foam-absorbers/
http://www.lairdtech.com/product-categories/rfmicrowave-absorbers-dielectrics
http://www.masttechnologies.com/rf-absorbers/
http://www.djmelectronics.com/rf-absorber.html