Spatially focusing a radio signal and simultaneously nulling it at another location using time-reversal signal processing

Phased array antenna techniques for beam-forming are thwarted in a cluttered environment. The time-reversal method utilizes the clutter (and associated multipath) to focus beyond the Rayleigh limit. This method makes use of the reciprocity of wireless propagation channels. Time-reversal can also be used to null signals, either to reduce unintentional interference or to prevent eavesdropping. We present a simple technique that nulls the transmitted signal at a specific location, while simultaneously focusing the signal at a desired location. This technique can also be used for the reverse problem of reception of a desired signal while nulling out an interfering source.