Radar system for detecting relative velocity and relative speed of a preceding vehicle

A radar system comprising a transmit antenna for alternately transmitting two signals on different frequencies, a receive antenna for receiving signals which were transmitted from said transmit antenna and reflected back on a preceding object, a first digitizing means for sampling and digitizing respectively said received signals, and a first analyzing means for analyzing the frequencies of said digitized receive signals, extracting a peak spectrum, and computing a range rate of said object from the frequency of said peak spectrum;

• wherein said radar system further comprises a second digitizing means for sampling and digitizing respectively said received signals, a second analyzing means for analyzing the frequencies of said receive signals digitized by said second digitizing means, extracting a peak spectrum, and computing a range rate of said object from the frequency of said peak spectrum, and an output means for outputting selectively either the range rate computed by said first analyzing means or the range rate computed by said second analyzing means;
• said first analyzing means stores, as a threshold, a frequency which is within an analyzable low frequency range and higher than a minimum analyzable frequency;
• said second digitizing means samples and digitizes said received signals at a higher sampling resolution than the sampling resolution of said first digitizing means so that said second analyzing means may be able to analyze frequencies below said threshold;
• and said first analyzing means causes said second digitizing means and said second analyzing means to work when said received signals have a peak spectrum below said threshold.