In the last years, in order to fit the requirements of automotive radar application under the multi-target conditions, several proposals about Continuous Waveform (CW)have been developed. The transmit signal with Multiple Frequency Shift Keying (MFSK) technology was developed to analyze the target information in range domain and Doppler frequency domain simultaneously, but the MFSK waveform has lower estimation accuracy in phase measuring. A higher accuracy signal type is the chirp sequence waveform of monopulse radar, which is based on two-dimension independent frequency measuring. It can also get the range and velocity information, but might lead to ambiguities in Doppler domain. To avoid the Doppler ambiguity, a method is proposed in this paper, which uses the modified chirp sequence waveform. The carrier frequencies of the modified chirp sequence are different, which causes the Doppler frequency offset. Doppler ambiguities have no influence on the Doppler frequency offset and the speed of targets can be derived from carrier frequency offset and Doppler frequency offset. Thus, the modified chirp sequence avoids the ambiguities in velocity and guarantees the measurement accuracy even in multi-target conditions. It has advantages in the automotive radar applications.
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