Thursday, 28 July 2016

Why is signum function used to calculate Fourier transform of unit step function


I read in a standard textbook that the Fourier transform of unit impulse function is calculated with the help of approximations and signum function as the integration of unit impulse does not converge. What's so special about signum function that it is used to calculate Fourier transform? I tried to find out an approximation as:


$$ \lim_{ a \rightarrow 0 } \int_{-\infty}^{+\infty} e^{-at} u(t) e^{-j\omega t} dt $$


But I am getting wrong result. Why is this so?




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