The design and development of real-time beamformers using multirate digital signal processing techniques

This thesis presents the design, development, and implementation of real-time beamformers for passive sonar applications requiring the production of a single beam. An efficient interpolation beamforming algorithm based on the polyphase filter structure is developed, and the adaptation of this algorithm for a near-field application is presented. The architecture of a real-time beamforming system based on the polyphase filter structure is discussed. Real-time processing concepts such as multiple data buffers, pipeline processing, and overlap-save processing are emphasized.

In addition, the thesis discusses circular convolution effects that occur when the delay property of the fast Fourier transform (FFT) is used to achieve fractional sample delays in a frequency domain beamformer. The concept of integer and fractional sample delays developed for the polyphase filter algorithm is applied to the frequency domain to eliminate the effects of circular convolution. The implementation of an FFT beamformer based on this concept is presented. Special emphasis is placed on the use of windowed delay filters for fractional sample generation and a set of prestored basis vectors for integer delay generation.