An implementation of the chirp transform algorithm for performing a real-time Fourier transform is described. The implementation is based upon an acousto-optic convolver with a large time-bandwidth product An instantaneous bandwidth of about 75 MHz was achieved for the Fourier transformer with a dynamic range in excess of 60 dB for a cw time-gated waveform. By using an almost-uniform light-beam intensity across the device, the measured sidelobe amplitudes were within 0.5 dB of the theoretical values. The corresponding measured phase errors were less than 5°. The adaptability of this acousto-optic implementation is demonstrated by the ease with which one can vary both the sidelobe weighting function and the time rate of the transform.
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