Why must X(s) occur in conjugate reciprocal pairs for a real x(t)?

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For a real x(t), the Fourier or Laplace transform X(s) typically exhibits conjugate reciprocal pairs unless x(t) is of a specific form. When x(t) is an exponential function like e^{at}, X(s) can have a real pole at s = a, indicating that not all transforms yield conjugate pairs. In contrast, sinusoidal x(t) results in complex conjugate poles in X(s). This distinction highlights the relationship between the nature of x(t) and the characteristics of its transform X(s). Understanding these properties is crucial for analyzing signal behavior in the frequency domain.
khdani
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Hello,
if i said that x(t) is real,
why X(s) must occur in conjugate reciprocal pairs ?
 
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It does not.
If x(t) = e^{at}, then X(s) = \frac{1}{s-a}, which has a real pole at s = a.
In the other way, if x(t) is a sinusoid, then X(s) will have complex conjugate poles.
 
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