In one embodiment, a source device includes one or more tunable elements associated with an antenna. The source device is operable to modulate an impedance of one or more tunable elements based on a sequence of tuning vectors, measure a reference signal amplitude for each tuning vector, and determine field amplitudes for an array of reference points that circumscribe at least a portion of the source device based on the reference signal amplitude for each tuning vector. The source device is further operable to determine a target tuning vector that defines a target radiation pattern based on the field amplitudes, and transmit a target signal to a target device based on the target radiation pattern.