TABLE OF CONTENTS The radar ambiguity function is defined as the absolute value of the envelope of the output of a matched filter when the input to the filter is a Doppler-shifted version of the original signal, to which the filter was matched [1]. If s( t) is the complex envelope of the signal, then the ambiguity function is given by ([1], p. 120)
| (3.1) |  |
The filter was originally matched to the signal at a nominal center frequency and a nominal delay. Thus, X (0, 0) is the output when the input signal is returned from a point target at the nominal delay and Doppler shift for which the filter was matched. The two parameters of the ambiguity function are an additional delay ? and an additional frequency shift v. Therefore, any value of ? and/or v other than zero, indicate a return from a target at some other range and/or velocity. The ambiguity function peaks at ? = 0, v = 0 and is zero everywhere else. This will correspond to an ideal resolution between neighboring targets. However, we will see that such a shape of the ambiguity function is impossible to attain. Furthermore, even if we could, such a narrow function would not permit a radar to find a previously undetected target, because the probability of that target lying within the response region would be near zero. One requirement on a radar waveform is that it must be possible...
