What if you could design a satellite dish or microwave antenna with the feed horn behind the reflector instead of in front of it? That may be possible, thanks to research by Cesar Monzon, a senior scientist at Enig Associates presented in the paper Anomalous Power Flow and 'Ghost' Sources published in Physical Review Letters (payment required to view the full paper).

The abstract describes the effect this way:

"It is demonstrated that EM radiation from complex sources can result in real power in restricted regions of space flowing back towards the sources, thereby mimicking 'ghost' sources. This counterintuitive mechanism of radiation does not rely on backward waves, as ordinary waves carry the power. Ways to harness the effect by making it directional are presented, together with selected applications, of which deception is a prime example due to the nature of the phenomenon."

It goes on to say that this concept could be to such areas as mechanics, acoustics and others with technology that is already available.

The article In radiation 'ventriloquism,' electromagnetic waves travel backwards on Physorg.com describes how the waves are generated and listed some of the possible applications. Obviously hiding transmitters and radar emitters is desirable in military environments.

Physorg.com quotes Monzon describing how the technology could be used with dish antennas: "On the case of satellite antenna feeds, the theory indicates it may be possible to build these behind the main reflector dish, which will offer a clear field of view without blocking or the disadvantages derived from feed offsetting. The same principle applies to both transmit and receive antennas."