Stepped-frequency radar has the ability of high range resolution(HRR).It normally adopts frequency-time transformation(IDFT) processing to get the range profile of targets.Alternatively stepped-frequency radar can also use time-frequency transformation(DFT) processing

with which it is seen as a kind of pulsed-doppler(PD) radars that use stepped-frequency pulses. Through parametric design and signal processing methods of the radar system

DFT method can achieve both unambiguous velocity and high resolution ranging in a single dwell under HPRF circumstances.The range ambiguity problem in HPRF PD radars can be resolved by careful design of parameters and signal processing methods.This paper analyzes the time-frequency transformation processing of stepped-frequency radars

based on which the HPRF PD stepped-frequency radar system’s parameter design principle

solutions to the frequency-time coupling issue and range ambiguity are also given.Both theoretical analysis and simulation result prove that this radar scheme can simultaneously achieve unambiguous velocity and high resolution ranging.