Broadband Beamforming and Direction Finding Using Concentric Ring Array

Sensor arrays have been used widely in applications including radar, sonar, seismology, biomedicine, communications, geophysical exploration, astronomy, and imaging. A very popular type of sensor array is circular array. It has several advantages such as the fact that it can perform 360 scan around its center very conveniently and during the scan the array pattern can be kept almost invariant. In our research, we consider beamformer design and DOA estimation for a wideband source using concentric ring array(CRA) that contains many concentric rings of different radii. Such structure yields several advantages including the flexibility in array pattern synthesis and adaptive array design. Previous works on controlling the array pattern of CRA only address narrowband scenario. The research on CRA conducted here is aimed for broadband beamforming applications. The design of deterministic broadband beamformer, adaptive broadband beamformer and broadband direction of arrival(DOA) estimation using CRA are addressed in this research. The proposed deterministic as well as adaptive broadband beamformer designs use the novel idea of decomposing the weights of the array into two sets: inter-ring weights and intra-ring weights, and they are chosen separately using different criteria. The deterministic broadband beamformer design is based on the sidelobe level control method proposed by Stearns and Stewart for 2-D narrowband beamforming using continuous ring antennas. We propose three methods to design inter-ring weights to achieve desirable sidelobe and/or mainlobe in the array pattern at a range of frequencies. Method I uses an interpolation technique to derive the inter-ring weights at a range of frequencies that can yield the desired sidelobe level. Method II uses MMSE optimization to find the inter-ring weights that can reduce the pattern synthesis error when array elements are not enough. Method III improves on previous methods by selecting appropriate desirable prototype array pattern at different frequencies to achieve