Novel multirate processing of beamspace noise eigenvectors

A novel implementation of Root-MUSIC is introduced based on the observation that the MUSIC null spectrum created with a beamspace noise eigenvector is bandpass exhibiting nulls at the locations of in-band sources. Thus, after telescoping to element space and modulating to broad-side, the telescoped noise eigenvector may be decimated yielding a small order polynomial with the separation between signal roots increased by the decimation factor. Depending on the out-of-band response of the beamformers, the telescoped noise eigenvector may be passed through a lowpass filter prior to decimation to preserve in-band source nulls. A low cost algorithm is realized by invoking linearity and performing the modulation, filtering, and decimation operations a-priori on the beamformers yielding a transformation to be applied to the beamspace noise eigenvectors