b,==if(t)sin(ko )dt==jf(t)sin(ko, t)dt=if(t)sin(ko, )dt f(t)sin(ko, t)d(o, t) T-π (1式还可写成r(t)=A,+Amco(0t+v)+A-c0(2ot+v,)+…+ A cos(kot+v)+…+=A+∑Ac0s(kot+y) .'cos(ko, t+y =cos ko, t cosYk-sin Yk sin ko,t 恒定分量→A0=a0 A=√a+b.2ak=A-mC0Svk kI b b,=-A, sin y Y=arct(k) k 周期信号=一系列谐波之和 2013 Kor 频谱图:将各个频率对应的振幅用线段画现来-振幅频谱 还有相位频谱:相位按频率的分布。周期信号 一系列谐波之和 恒定分量 式还可写成 = =   = → = = + =   +  =   −    +  + + = +  +  = +  +  +  +  + +    =   =  =  =       =  −  − ) a -b b -A sin arctg( A a A a b a A cos cos(k t ) cosk t cos sin sink t A cos(k t ) ... A A cos(k t ) ( ) f(t) A A cos( t ) A cos( t ) ... f(t)sin(k t)d( t) f(t)sin(k t)dt f(t)sin(k t)dt T f(t)sin(k t)dt T b k k k k m k k k am k 2 k 2 0 k m k k K K K k m k k m k 0 1 m m T T T k 0 1 2 1 2 2 1 1 1 1 1 1 0 1 1 1 2 1 2 1 1 2 0 1 2 2 1 0 1  Akm ω·1 2ω1 3 ω1 K ω1 频谱图：将各个频率对应的振幅用线段画现来------振幅频谱 还有相位频谱：相位按频率的分布