幅频和相频特性分别在两个图窗，不在一起方便保存，无需再裁剪

clear;  close all;
k = 1;
numH = 1;
denH = [1,k];
sysH = tf(numH,denH);
w = logspace(-2,2);

[mag, phase] = bode(sysH,w);

% 幅频特性
loglog(w,squeeze(mag));grid on;
% 相频特性
semilogx(w, squeeze(phase));grid on;