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1 October 1999 Adaptive beamforming with TDI CCD-based true-time-delay processing
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We present an adaptation of the BEAMTAP (Broadband and Efficient Adaptive Method for True-time-delay Array Processing) algorithm, previously developed for wideband phased array radars, to lower bandwidth applications such as sonar. This system utilizes the emerging time or wavelength multiplexed optical hydro-phone sensors and processes the cohered array of signals in the optical domain without conversion to the electronic domain or digitization. Modulated signals from an optical hydro-phone array are pre- processed then imaged through a photorefractive crystal where they interfere with a reference signal and its delayed replicas. The diffraction of the sonar signals off these adaptive weight gratings and detection on a linear time- delay-and-integrate charge coupled device (TDI CCD) completes the true-time-delay (TTD) beamforming process. Optical signals focused on different regions of the TDI CCD accumulate the appropriate delays necessary to synchronize and coherently sum the acoustic signals arriving at various angles on the hydro-phone array. In this paper, we present an experimental demonstration of TTD processing of low frequency signals (in the KHz sonar regime) using a TDI CCD tapped delay line. Simulations demonstrating the performance of the overall system are also presented.
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Andrew M. Kiruluta, Gregory Kriehn, Paulo E. X. Silveira, Samuel P. Weaver, Shawn Kraut, Kelvin H. Wagner, and Dana Z. Anderson "Adaptive beamforming with TDI CCD-based true-time-delay processing", Proc. SPIE 3804, Algorithms, Devices, and Systems for Optical Information Processing III, (1 October 1999);

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