Redirective and retrodirective antenna arrays

The problem considered is the redirection of a time-varying signal from one specified point to another by a set of arbitrarily spaced antenna array elements. The necessary and sufficient condition for signal redirection is determined without restricting the analysis to a monochromatic signal. This condition, which involves time delays only, is valid for signal redirection in general and hence, in particular, for retrodirection. Once the condition for redirection is satisfied, the amplitude of the signal retransmitted from each array element can be chosen at will Proper adjustment of these amplitudes will maximize the amplitude of the redirected signal as received at the specified point. The appropriate criterion for maximization is derived. In addition, the problem of noise (undesired signal) generation due to errors in the time delays is considered.