![]() Usually when you're introducing LFM, you'll show the modulated pulse itself as well as the phase progression in the time-domain. It also plays with the plot views and most likely unwraps the phase angles, which is usually required to see the phases you expect. ![]() The book presents the analytical expression for the LFM spectrum, which is an approximation. The book is not wrong, but it does present the concepts on LFM in a clunky manner and can be misleading. Note: see comments below accepted answer for further info. Update: turns out magnitude doesn't spike, but rather decays exponentially, which is far from the expected horizontal line - and, the phase is linear: Further, the left peak appears to scale with N, behaving more like an impulse in the limit, which won't yield zero energy as in Gibbs phenomenon. I figure, in the limit N -> inf, the amplitude spike has zero width (like in Gibbs) - but this appears contradicted in the "large N long padding" case, where a nontrivial portion of the amplitude decays with oscillations. Zero-padding appears to correct phase (quadratic if unrolled), and more samples tend to flatten the magnitude for an ever-growing portion of frequencies to the right. To address each, I try greater N, and zero-padding - below. Still, DFT should resemble a sampled DTFT.ĭFT time-domain periodicity, whereas DTFT assumes aperiodic, or "repeats at infinity" with infinite zero-padding. 223 claims so, yet my results via DFT differ:ĭFT vs DTFT: "frequency response" is computed via latter. ![]()
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