Broadband superdirective beamforming using multipole superposition

In sensor array processing, beamforming techniques are applied in order to form a directivity characteristic, the so-called beam pattern, allowing the sensor array to distinguish signals depending on their impinging direction. A common problem is that directivity is usually achieved only above a certain minimum frequency determined by the array size, such that effective beamforming at low frequencies requires large array dimensions. In this paper, a method is shown to build a desired beam pattern using compact, superdirective multipole sensor arrays which are sized far below the regarded wavelengths and at the same time produce an almost frequency-invariant beam pattern.