matlab画伯德图（带谐振点和-3dB带宽）

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P=bodeoptions;
P.Grid='on';
P.XLim={[1e-2,100]};%设置横轴范围
P.FreqUnits='Hz';%将横坐标单位换位HZ
P.YLim={[-30,3],[-135,10]};%设置纵轴范围
num1=[30,369.8,1367];
den1=[2.152E-4,0.2704,29.99,358.9,1367];
Gx_validation=tf(num1,den1);
[mag,phase,wout]=bode(Gx_validation,P)
%bode(Gx_validation,P)
margin(Gx_validation)

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%this function is to calculate the bode diagram without using bode function
%directly.
figure(1);
%% -----限定坐标轴输出范围-----
axisxmin=1e-2;
axisxmax=1e2;
axisyminmag=-inf;
axisymaxmag=4;
axisyminpha=-inf;
axisymaxpha=45;
%% -----幅频图------
subplot(2,1,1);
f=logspace(-2,2,10000);
%频率采样，利用logspace在横坐标log之后均匀取点，防止线性取点后画图时的不均匀
w=f*2*pi;
wi=complex(0,w);
%使角频率和虚数单位结合
%输入系统传递函数
G=(30*(wi).^2+127.9*wi+163.6)./(1.244e-3*(wi).^4+0.7818*(wi).^3+29.99*(wi).^2+124.1*wi+163.6) ;
magnitude=20*log10(abs(G));
%幅度换算为dB单位
semilogx(f,magnitude);
title('G_{a_Z} Bode Diagram');
axis([axisxmin,axisxmax,axisyminmag,axisymaxmag]);
box on;
%xlabel('frequency (Hz)','Fontweight','bold','FontSize',20);
ylabel('Magnitude (dB)','Fontweight','bold','FontSize',20);
grid minor;
%加密网格
set(gca,'xticklabel',[])
%去掉横坐标数字
set(gca,'GridLineStyle','-','XGrid','on','YGrid','on');
%添加横坐标和纵坐标的网格
set(gca,'FontSize',10,'Fontweight','bold');
%调节坐标轴字体大小粗细
hold on;
%% -----相频图------
subplot(2,1,2);
phase=angle(G)*180/pi;
%取虚数幅角值，并转换弧度为角度
semilogx(f,phase);
axis([axisxmin,axisxmax,axisyminpha,axisymaxpha]);
box on;
xlabel('frequency (Hz)','Fontweight','bold','FontSize',10);
ylabel('Phase (deg)','Fontweight','bold','FontSize',10);
grid minor;
%加密网格
set(gca,'GridLineStyle','-','XGrid','on','YGrid','on');
%添加横坐标和纵坐标的网格
set(gca,'FontSize',10,'Fontweight','bold');
%调节坐标轴字体大小粗细
hold on;
%% -----添加谐振点-----
subplot(2,1,1);
[magmax,fmax] = max(magnitude);
%谐振点为幅频曲线的极值点
fmax = f(fmax);
plot(fmax,magmax,'o','LineWidth',2,'MarkerSize',5,'MarkerEdgeColor','k')
text(fmax,magmax-2,sprintf('Resonance point:n(%.3f Hz, %.3f dB)',fmax,magmax),...
'VerticalAlignment','top','HorizontalAlignment','right')
%'VerticalAlignment','bottom'
hold on;
%% -----添加-3dB带宽-----
B=abs(magnitude+3);
[x,index]=sort(B);
%为了得到最接近-3dB的值，先对绝对值进行排序，index为排序前的坐标值
mag_3db=magnitude(index(1));
f_3db=f(index(1));
plot(f_3db,mag_3db,'o','LineWidth',2,'MarkerSize',5,'MarkerEdgeColor','r')
text(f_3db,mag_3db,sprintf('Cut-off point:n(%.3f Hz, %.3f dB)',f_3db,mag_3db),...
'VerticalAlignment','bottom','HorizontalAlignment','left')
%在目标坐标点处添加文字