Abstract: A method and apparatus for eliminating the sidelobe ambiguity in the range esponse of an FM-CW radar. An FM-CW signal with a periodic modulation frequency is transmitted and reflected from a target, received and combined with a sample of the transmitted signal to provide a combination signal. A portion of this combination signal including a selected harmonic and next adjacent harmonic is amplified and mixed with reference signals comprising the selected harmonic and next adjacent harmonic to provide two separate difference signals. These signals are in turn low pass filtered and further mixed to provide a range response with a mainlobe of one polarity and all side lobes of an opposite polarity. The energy under the mainlobe is detected and integrated to provide a voltage signal. When this voltage signal reaches a preset threshold level a further signal is generated.