4 The continuous time Fourier transform 2)Fourier transform representation of Aperiodic sIgnal For periodic signal x(t) ae TJr x(te-jkootdt For aperiodic signal x(t x()=1im()或X()-120>x()4 The continuous time Fourier transform (2) Fourier transform representation of Aperiodic signal        = =   − + =− T j k t k k j k t k x t e dt T a x t a e 0 0 ( ) 1 ~ ( ) ~   For periodic signal : ( ) ~ x t For aperiodic signal x(t) : ( ) ( ) ~ ( ) ~ ( ) x t limx t x t x t T T = ⎯ → ⎯ → → 或