TABLE OF CONTENTS Many of the ELINT signals of interest consist of pulses particularly radar signals. Determining the character of the intrapulse modulation gives valuable insight into the radar s function and design. The term intrapulse refers to the shape of the pulse envelope (or amplitude modulation function) and also to the frequency or phase variations within the pulse. If the carrier is not frequency modulated, the pulse is sometimes referred to as a CW pulse. (This term is sometimes used in radar literature and simply means a pulse with no intentional frequency or phase modulation.) If there is no intentional FM or PM within the pulse, the envelope of the pulse determines the range resolution of the radar. If there is intentional FM or PM, demodulating it (or determining its bandwidth) gives insight into the range resolution or other functions of the radar. Examining the unintentional AM and FM or PM can sometimes provide insight into the transmitter type and may help to identify the signal.
The radar waveform designer, of course, does not consider the individual pulses as an isolated parameter but must consider the entire modulating function, including the pulse intervals and phase or frequency modulation. The radar waveform determines its ambiguity function, [1] which is essentially the autocorrelation of the waveform with itself as it would appear if reflected from a point target having range delay ? and Doppler shift f d. This function is plotted in three dimensions as magnitude versus range delay and radial...
