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% [rect_A,dt_A]=cp0101_genrect(1e-1,1000,0);
[rect_B,dt_B]=cp0101_genrect(1e-1,1000,1e3);
% cp0101_bandwidth1(rect_A,dt_A,-3);
cp0101_bandwidth1(rect_B,dt_B,-10);
function [ss_E,f_high,f_low,BW]=cp0101_bandwidth1(signal,dt,threshold)
%計(jì)算固定取樣周期“dt”的“signal”的帶寬，以及計(jì)算帶寬所需的預(yù)知threshold
%step1計(jì)算輸入數(shù)據(jù)單邊功率密度譜（ESD）
fs=1/dt; %采樣頻率
N=length(signal); %樣本數(shù)量
T=N*dt; %窗口時(shí)間
df=1/T; %基本頻率
X=fft(signal); %快速傅里葉變換，也叫離散傅里葉變換，轉(zhuǎn)換后為離散的雙邊振幅頻譜
X=X/N; %matlab頻譜轉(zhuǎn)換為傅里葉頻譜
ds_E=abs(X).^2/(df^2); %雙邊ESD//abs(X)對(duì)X取絕對(duì)值
ss_E=2.*ds_E(1:floor(N/2)); %單邊ESD
%STEP2我們利用迭代算法計(jì)算出相對(duì)于特定閾值的ESD的最高和最低頻率，
%從而估算出被檢測(cè)信號(hào)所占用帶寬。這種算法同時(shí)適用于基帶信號(hào)和已調(diào)制信號(hào)
[Epeak,index]=max(ss_E); %Epeak為單邊ESD的峰值，index是該峰值所在位置
f_peak=index*df; %頻率峰值
Eth=Epeak*10^(threshold/10);
imax=index;
E0h=ss_E(index);
while (E0h>Eth)&(imax<=(N/2))
imax=imax+1;
E0h=ss_E(imax);
end
f_high=(imax-1)*df;
imin=index;
E0l=ss_E(index);
while (E0h>Eth)&(imin>1)&(index>1)
imin=imin-1;
E0l=ss_E(imin);
end
f_low=(min(index,imin)-1)*df;
BW=f_high-f_low;
fprintf('\nFrequency Bandwidth = %f [HZ]\n High Frequency= %f [HZ]\nLow Frequency= %f [HZ]\n',BW,f_high,f_low);
%step3 畫(huà)圖
figure(2)
frequency=linspace(0,fs/2,length(ss_E));
PF=plot(frequency,ss_E);
set(PF,'LineWidth',[2]);
L1=line([f_high f_high],[min(ss_E) max(ss_E)]);
set(L1,'Color',[0 0 0],'LineStyle',':');
L1=line([f_low f_low],[min(ss_E) max(ss_E)]);
set(L1,'Color',[0 0 0],'LineStyle',':');
L1=line([f_low f_high],[Eth Eth]);
set(L1,'LineWidth',[2],'Color','red','LineStyle',':');
axis([0.8*f_low 1.2*f_high -0.1*Epeak 1.2*Epeak]);
AX=gca;
set(AX,'FontSize',12);
T=title('Frequency domain');
set(T,'FontSize',14);
X=xlabel('頻率 [Hz]');
set(X,'FontSize',14);
Y=ylabel('單邊ESD [V^2S/Hz]');
set(Y,'FontSize',14);
end

復(fù)制代碼