Spatial encryption using a retrodirective antenna array

In this paper we show how a 2.4 GHz retrodirective array operating in a multipath rich environment can be utilised in order to spatially encrypt digitally encoded data. For the first time we show experimentally that digital data which has no mathematical encryption applied to it can be successfully recovered only when it is detected within a highly constrained spatial region co-located close to the position of the CW reference signal. This means that the signal cannot be intercepted and its modulated data recovered at locations other than the constrained spatial region around the position from which the retrodirective communication was initiated. Thus we say that it is spatially encrypted.