Fourier transform

The Fourier Transform represents a function as a "linear combination" of complex sinusoids at different frequencies . Fourier proposed that a function may be written in terms of a sum of complex sine and cosine functions with weighted amplitudes.

In Euler notation the complex exponential may be represented as:

Thus, the definition of a Fourier transform is usually represented in complex exponential notation.

The Fourier transform of s(t) is defined by

Under appropriate conditions original function can be recovered by:

The function is the Fourier transform of . This is often denoted with the operator , in the case above,

The function must satisfy the Dirichlet conditions in order for for the integral defining Fourier transform to converge.

Forward Fourier Transform(FT)/Anaysis Equation

Inverse Fourier Transform(IFT)/Synthesis Equation

Relation to the Laplace TransformEdit

In fact, the Fourier Transform can be viewed as a special case of the bilateral Laplace Transform. If the complex Laplace variable s were written as  , then the Fourier transform is just the bilateral Laplace transform evaluated at  . This justification is not mathematically rigorous, but for most applications in engineering the correspondence holds.


× Time Function Fourier Transform Property
1     Linearity
2     Duality
3  , c = constant   Scalar Multiplication
4     Differentiation in time domain
5    , if   Integration in Time domain
6     Differentiation in Frequency Domain
7     Time reversal
8     Time Scaling
9     Time shifting
10     Modulation
11     Modulation
12     Frequency shifting
13     Convolution