Near field superdirectivity (NFSD)

In some array applications, the source of interest is close to the array, so that we have to use a near-field model. Almost always the near-field is considered as an additional difficulty. We contradict this point of view and show that if the desired source is in the near-field and the other sources are in the far-field, then even a small array can be at the same time highly directive and comparatively robust. Instead of relying on small phase differences for low frequencies, we fully exploit the fact that the amplitude vector of the source of interest is different from that of any other source. The array geometry should be chosen to enhance this effect. Unlike far-field superdirectivity, we can steer the main lobe to arbitrary directions without prohibitive loss of performance. We applied our method to microphone array sound pick up for workstations. Simulation results and measurements of a real time implementation on a fixed point DSP are provided.