The linear FM waveform that provides the desired range resolution can be constructed as follows. Now, explore the linear FM waveform in detail. This improvement occurs even though the Doppler resolution of a linear FM waveform is still given by the reciprocal of the pulse width. The longer pulse width also improves the Doppler resolution. Instead, the range resolution is determined by the sweep bandwidth.Ī system that transmits a linear FM waveform can afford a longer pulse width, which alleviates the power requirement. The range resolution of a linear FM waveform no longer depends on the pulse width. Linear FM waveform is just such a waveform. One can then improve the resolution in both domains simultaneously. Therefore, one way to solve this issue is to come up with a waveform that decouples this dependency. The root issue here is that both the delay and the Doppler resolution depend on the pulse width in opposite ways. Apparently, there exists a conflict between range and Doppler resolutions of a rectangular waveform. At the same time, the range resolution of a rectangular waveform is proportional to the pulse width. In fact, the Doppler resolution of a single rectangular pulse is given by the reciprocal of the pulse width. One can see from the previous section that a single rectangular pulse has poor Doppler resolution. In practice, producing such power can be very costly. Hence, a narrow pulse width requires very high peak power at the transmitter. At the same time, the system also needs to be able to send out enough energy to the space so that the returned echo can be reliably detected. Thus, to achieve good range resolution, the system needs to adopt a very small pulse width. Another issue with the rectangular waveform is that the range resolution is determined by the pulse width.
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