Superdirectivity and SNR constraints in wideband array-pattern design

Wide instantaneous and tunable-bandwidth arrays pose a challenging design problem. Since the elements are usually spaced close to one-half wavelength at the highest frequency of operation, at lower frequencies the array may be considerably oversampled spatially. In a conventional time-delay-steered array the result is a beamwidth that is proportional to frequency. With a FIR filter at each element, however, superdirectivity can be achieved at lower frequencies, improving the beam characteristics. Constraints on efficiency, sensitivity, and SNR are derived to limit the undesirable effects of superdirectivity.