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英文誌(2004-)

Journal of Medical Ultrasonics

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1997 - Vol.24

Vol.24 No.12

Original Article(原著)

(1809 - 1825)

4周期法による高限界速パルスドプラ計測における不等間隔パルス送波方式の信号対雑音比の改善

Four-Pulse Repetition Time Method (4-PRT) to Improve Signal-to-Noise Ratio in Non-equally Spaced Pulse Transmission

西山 久司

Hisashi NISHIYAMA

(株)日立製作所防衛技術推進本部

Defense Division Hitachi, Limited

キーワード : Four-Pulse Repetition Time Method, Nonaliasing, Non-equally spaced pulse transmission, Pulsed Doppler, S/N

Methods have been developed for improving the signal-to-noise ratio (S/N) in the non-equally spaced pulse transmission method (NST or 2-PRT) for non-aliasing pulsed Doppler measurement. 2-PRT can be provided for the region T/Ts times the Nyquist frequency without decreasing the range when two pulse repetition times (PRT), T and T+Ts (Ts<<T), are known. Blind speed results from null frequency of the moving target indication (MTI) filter, however, as well as when S/N is degraded by the complex autocorrelation of correlation signal. We used the proposed 4-PRT method, applying the MTI filter based on either the respective-PRT-MTI or the sum-PRT-MTI technique to prove that the problem of blind frequency can be resolved. The S/N improvement method in 4-PRT makes it possible to increase the numbers of the addition of the difference vector between two phase differences without transmitting additional pulses, so that its S/N can be improved. In the proposed phase difference correction algorithm, the reference parameter obtained by 4-PRT is used to correct aliasing of phase difference, while Doppler frequency can be obtained with the conventional S/N. Measurement results obtained using synthesized Doppler signals and white noise show the respective PRT-MTI technique to be superior to the sum-PRT-MTI from the point of view of S/N in the calculation of 2-PRT. We further demonstrate that 4-PRT used in conjunction with the respective-PRT-MTI can remove blind frequency, and its S/N improvement method can reduce estimated error. The phase difference correction algorithm provides the Doppler frequency measured in the region 5 (T/Ts) times higher than the Nyquist frequency, but with almost the same S/N.