以单频正弦信号为激励测量系统频率响应

以单频正弦信号为激励测量系统频率响应

一、实验目的

1.加深对LTI系统频率响应物理概念的理解

2.掌握测量LTI系统频率响应基本方法

3.掌握频率域采样法设计FIR滤波器的原理

4.掌握根据实际需求正确选择DFT参数的方法

二、实验原理与方法

三、源程序：

clear;

b=[0.0002,0.0002,-0.001,-0.0006,0.0023,0.0009,-0.0036,-0.0004,0.0042,-0.0004,-0.0036,0.0009, 0.0023,-0.0006,-0.001,0.0002,0.0002];

a=[1,2.675,7.8559,13.6147,23.8512,30.8819,39.641,40.2748,40.3641,32.5164,25.859,16.1752,10 .0665,4.5598,2.1127,0.5587,0.1695];

freqz(b,a);hold on;

n=0:1000;

w=zeros(1,500);

i=1;

for w0=0:.002:1;

x=cos(pi*w0*n);%令A=1；初相为0；

y=filter(b,a,x);

xw=fft(x,1024);

yw=fft(y,1024);

%figure;

%subplot(2,1,1);

%stem(0:1023,abs(xw));grid on;

%subplot(2,1,2);

%stem(0:1023,abs(yw));grid on;

h=max(abs(yw))/max(abs(xw));

H=20*log10(h);

w(i)=H;

i=i+1;

end

%subplot(2,1,1);

%stem(0:511,abs(xw));grid on;

%subplot(2,1,2);

%stem(0:511,abs(yw));grid on;

%figure

%w=polyfit(0:0.001:1,w,3);

plot(0:.002:1,w,'r');grid on;

a1=unwrap(angle(yw));

hold on;

subplot(2,1,2)

plot(0:1/1023:1,-a1);grid on;

%figure

%plot(0:1023,abs(yw));grid on;title('测量系统的幅频响应')

绘得图形：

00.10.20.30.40.50.60.70.80.91

-40-20

20

40

00.10.20.30.40.50.60.70.8

0.91

-150-100

-50

050

Normalized Frequency ( rad/sample)M a g n i t u d e (d B

)