|John Hoffman, Louis Vasquez,
Charles Farthing, and Clarence Ng
Systems Engineering Group, Inc.
tel: (410) 381-8740, ext. 131
Abstract The system level clutter improvement factor (CIF) in heavy distributed clutter environments, such as the littoral environment, is limited by radar instabilities. In many radar systems the two largest instabilities are transmitter intrapulse noise and A-to-D converter quantization noise. A-to-D converter dynamic ranges are increasing at typical radar sampling rates leaving transmitter intrapulse noise (IPN) as the limiting factor for CIF performance. A pulse Doppler mode can be used to increase CIF through coherent integration gain, but the additional pulses required put a severe load on radar resources particularly for horizon search modes.
An alternative approach to improving radar system CIF performance is to employ MTI and cancel the transmitter IPN using advanced signal processing techniques. One approach is to measure the in-phase and quadrature components of the pulse compression coded transmit pulse on a chip-by-chip basis. The measured transmit pulse data is then applied to the radar return during signal processing to cancel the IPN.
A frequency domain de-convolution approach for transmitter noise cancellation is being developed. The time domain radar return from distributed clutter is the convolution of the coded transmit pulse and the distributed clutter field. By taking the Fast Fourier Transform (FFT) of the distributed clutter return, the IPN contribution of the noisy transmit waveform can be removed by dividing it by the frequency spectrum of the measured transmit waveform. An IFFT is used to return to the time domain for subsequent MTI processing.
The ADDCIF approach and its overall system performance capability will be summarized. Simulation results for coded waveforms will be presented which show the potential of the approach for canceling radar transmitter intrapulse noise. The results of MTI processing of measured radar return data from the AEGIS Combat System Center (ACSC) in Wallops Island, Virginia using the ADDCIF algorithm will be compared with simulation results.
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