A waveguide as it pertains to RF is just an enclosed hollow metal pipe that can carry RF energy. The size of the tube determines the ideal frequency it can carr

A waveguide as it pertains to RF is just an enclosed hollow metal pipe that can carry RF energy. The size of the tube determines the ideal frequency it can carry (without excessive losses). I believe at 2.4GHz, a common waveguide is roughly the diameter of a tennis ball cannister, so it's probably easy to put a directly a rat inside the waveguide (I can't read the article so I'm not sure if they do this). In theory though, there is no reason a directional antenna couldn't be used to deliver the same amount of power, the waveguide might simply be more convenient.