ch3_02_bien_doi_f.pdf
TRANSCRIPT
2/5/20151Chng 3CHUI FOURIER V BIN I FOURIERNi Dung1. Mt s dng tn hiu quan trng2. Khi nim hm tun hon3. Chui Fourier Khai trin Fourier4. Tch phn Fourier Bin i Fourier5. Phn tch ph tn hiu2/5/201523.4 TCH PHN FOURIER BIN I FOURIERBin i Fourier Cp bin i Fourier dng phc: = 12
= ()
K hiu:
= 1 = () 1()2/5/20153VD: =
= ; <
; Tm bin i Fourier. = = =
2
2
=
/2/2= /2 /2= 2
sin 2VD: = = ; <
; = 2
sin 2
= 2
sin 2= 2
sin 2
2
2= 2
2 sin 2
2= Sinc 2= Sa 2Nhc li, Sinc = sin
S = sin
2/5/20154Tnh Cht Ca Bin i FOURIER Tnh tuyn tnh Tnh cht i xng Thay i t l thi gian Php dch min thi gian Php dch min tn s Vi phn min thi gian Tch phn min thi gian Vi phn min tn s nh l nhn chp tn s nh l moun Parseval nh l nhn chp trongmin thi gian nh l iu ch2/5/20155Tnh Cht Ca Bin i FOURIER
()1) Tuyn tnh
1
1()
2
2()
1
1 +2
2
1
1() +2
2()2) Thay i t l thi gian 1
3) Tnh cht i xng
2()4) Dch min thi gian 0
0
Tnh Cht Ca Bin i FOURIER
()5) Dch min tn s
0 06) Tch phn min thi gian
+ 0 7) Vi phn min thi gian
8) Vi phn min tn s
2/5/20156VD: = =
; < ; Tm bin i Fourier. = = =
= =
+ 2
2
2
sin 2
+ 2
+
2
2
sin 2;
2
2
2
sin 2; = =
2
sin 2
2
2
= 2
2
sin 2
2
2
2= 2
2
sin 2sin 2VD: = =
; < ; 2/5/20157VD: = =
; < ; = 2
2
sin 2sin 2 =
22
sin2 2
=
= 1
22
sin2 2= sin2 2
22= Sa2 2VD: = =
; < ; = 2
2
sin 2sin 2 =
2
cos 1
=
= 1
2
cos 1=
2
2 cos 12/5/20158Tch Chp nh ngha =
1 . 2 = 1 2 = 2 1 nh l Parseval = =
=
2 =12
2 1) Tch chp min thi gian
1 2 12
1 2 2) Tch chp min tn s
1 2
1 2 nh l iu ch
() Tnh cht dch tn s
0
0
0 +0 nh l iu ch cos 0 12 0 + +0 sin 0 12 0 +02/5/201593.5 PHN TCH PH TN HIUWD: Phn Tch Ph Tn Hiu Phng php phn tch ph Tnh X(): = ()
Khi : th biu din bin ca F() theo tn s gi lph bin ca tn hiu f(t). Biu din gc pha ca F() theo cc tn s cachng gi l ph pha ca tn hiu f(t)2/5/201510VD: = . ; > Tm ph tn hiu. = = 0
+ = 1 + + 0=1 + = Ph bin : =1
2 +2 Ph pha: =
Ht chng 3