slide 17

Scientists have developed a method to increase range resolution without reducing pulse width. They use a chirped signal, which is a series of signals with increasing frequencies. Cross-correlation between low and high-frequency signals is low unless the template signal overlaps with the received signal. This method allows detection of high correlations even if objects are closer than half the pulse width. Range resolution now depends on the bandwidth of the chirped signal, not the pulse width. This process is called range compression. Some scientists developed an approach to increase the range resolution without shortening the pulse width, so the signal still has enough power to keep high SNR. The method transmits the chirped signal. The chirped signal is a series of signals whose frequencies increase linearly from low to high. The upper part of the figure is an easy illustration of the chirped signal in the spatial domain, and the lower part is the corresponding waveform. During the cross-correlation, the correlations between low-frequency signals and high-frequency signals are low. The correlation only becomes higher when the template signal overlaps with the received signal. Through this method, even if two objects are closer than half of the high-speed time's pulse width, their highest correlations still can be detected. The range resolution becomes dependent on the width of the bandwidth of the chirped signal, rather than the pulse width. The whole process is called range compression. We will see the illustration next slide.