The Performance of a Far-Field-Steering Applebaum Array with a Finite Distance Signal Source

The effect of the finite distance of the signal source on the performance of a far-field-steering Applebaum type adaptive array is examined. The output Signal-to-Noise Ratio (SNR) is expressed in terms of (1) the distance between the signal and the array center, (2) the input SNR, (3) the element number and locations, and (4) the signal direction. From that expression a rule of thumb is drawn to determine the distance between the signal source and the array center at which the degradation of the output SNR is ldB. That distance is in general much larger than the far-field range of a conventional beamforming array.