2、5,Rp=1dBws2=0.8,As=50dB根据设计要求查表知海明窗和布莱克曼窗都可以满足阻带衰减在50dB以上,在此我选择海明窗,因为海明窗的过渡带更窄。ws1=0.2*pi;wp1=0.35*pi;wp2=0.65*pi;ws2=0.7*pi;as=50;tr_width=min((wp1-ws1),(ws2-wp2));M=ceil(6.6*pi/tr_width)+1%计算Hamming的阶数n=[0:1:M-1];wc1=(ws1+wp1)/2;wc2=(wp2+ws2)/2;hd=ideal_lp(wc2,M)-ideal_lp(wc1,M);
3、%利用低通实现带通w_ham=(hamming(M))';h=hd.*w_ham;[db,mag,pha,grd,w]=freqz_m(h,[1]);delta_w=2*pi/1000;rp=-min(db(wp1/delta_w+1:1:wp2/delta_w))as=-round(max(db(ws2/delta_w+1:1:501)))subplot(2,2,1);stem(n,hd);axis([0M-1-0.40.5]);xlabel('n');ylabel('hd(n)')subplot(2,2,2);stem(n,w_ham);title('海
4、明窗')axis([0M-101.1]);xlabel('n');ylabel('w(n)')subplot(2,2,3);stem(n,h);title('实际的脉冲响应')axis([0M-1-0.40.5]);xlabel('n');ylabel('h(n)')subplot(2,2,4);plot(w/pi,db);axis([01-15010]);title('db形式的幅度响应');gridxlabel('以pi为单位的频率');ylabel('decibels')仿真波形仿真波形线性相位图用函数freqz(b,1,512)Rp=0.0448As
5、=53M=45对已给的信号进行滤波t=0:1/800:1;fs=1000;sig=sin(2*pi*80*t)+0.5*sin(2*pi*280*t)+0.2*sin(2*pi*440*t);subplot(2,2,1);plot(t,sig);ws1=0.2*pi;wp1=0.35*pi;wp2=0.65*pi;ws2=0.8*pi;as=50;tr_width=min((wp1-ws1),(ws2-wp2));M=ceil(6.6*pi/tr_width)+1n=[0:1:M-1];wc1=(ws1+wp1)/2;wc2=(wp2+ws2)/2;hd=i
6、deal_lp(wc2,M)-ideal_lp(wc1,M);w_ham=(hamming(M))';h=hd.*w_ham;b=h;对已给的信号进行滤波y=filter(b,1,sig);subplot(2,2,2);plot(t,y);s=fft(sig,512);%滤波前信号的频谱sf=fft(y,512);%滤波后信号的频谱w=(0:255)/256*500;subplot(2,2,3);plot(w,abs([s(1:256)']));xlabel('frequency(Hz)');ylabel('magoffouriertransform');g
7、rid;legend('beforefilter');subplot(2,2,4);plot(w,abs([sf(1:256)']));xlabel('frequency(Hz)');ylabel('magoffouriertransform');grid;legend('afterfilter');滤波前后信号频谱图sig=sin(2*pi*80*t)+0.5*sin(2*pi*280*t)+0.2*sin(2*pi*440*t);s=fft(sig,512);滤波前后信号频谱图y=filter(b,1,sig);sf=fft(y,512);此带通滤波器的
8、通带范围为175HZ到325HZ。可见把80HZ和4