: It is often troublesome

or even difficult

for the narrow band system in a coherent-pulse instrumentation radar to precisely track the radial speed of the target under conditions of low pulse repetition frequency of the radar and high speed and acceleration of the target.A method is given in this paper to bring about an all digital tracking system on the basis of modified DFT. Such system can track not only the radial speed of the target

but also its acceleration directly in conditions of low repetition frequency and high target speed and acceleration.The first part of the paper describes the influence of target radial acceleration on DFT. the modified DFT which can eliminate the said influence

and the two dimensional response characteristics of the frequency and the frequency changing rate of this modified DFT. The second part explains the method of eliminating speed ambiguity by repetition frequency agility. This method is based on solving residual equations for root and does no depend on target range information. The third part deals with the narrow band tracking loop based on modified DFT. Two dimensional error characteristics of the frequency and the frequency changing rate are presented

and a block-diagram of the system is also given.The author has conducted mathematical simulation of the above system. The results show that the accuracy in the measurement of radial speed and acceleration is quite satisfactory under the condition of comparatively low signal-noise ratio.