strange behavior of plot and freqz

Hello,

Does anyone knows why the freqz and the plot function display diffrent things?Shouldnt be the same?

For example in the first case everything seems fine but in the second the phase doesnt look the same.

This is my code:

close all;
clear all;

w = -pi:pi/128:pi;
z=tf('z');
G=(0.2*z/(z+0.2))*(1/(z-0.9));
[num,den]=tfdata(G,'v');
figure(1);
freqz(num,den,w);

[h, freq] = freqz(num, den, w);
phase = angle(h);
figure(2);
plot(freq, phase);

clear all;
w = -pi:pi/128:pi;
z=tf('z');
G=(0.2*z/(z+0.2))*(1/(z-0.9))*(1/(z-1));
[num,den]=tfdata(G,'v');
figure(3);
freqz(num,den,w);

[h, freq] = freqz(num, den, w);
phase = angle(h);
figure(4);
plot(freq, phase);

Answer 1

[Star Strider]

Thje angle functon returns angles in radians. If you add a call to the rad2deg function, the results will be in degrees, and the plots should look similar. It might also be necessary to use the unwrap function first.

w = -pi:pi/128:pi;
z=tf('z');
G=(0.2*z/(z+0.2))*(1/(z-0.9));
[num,den]=tfdata(G,'v');

[h, freq] = freqz(num, den, w);
phase = angle(h);
figure(2);
plot(freq, rad2deg(unwrap(phase)))

w = -pi:pi/128:pi;
z=tf('z');
G=(0.2*z/(z+0.2))*(1/(z-0.9))*(1/(z-1));
[num,den]=tfdata(G,'v');

[h, freq] = freqz(num, den, w);
phase = angle(h);
figure(4);
plot(freq, rad2deg(unwrap(phase)))

The aspect ratios are different because freqz produces subplot plots.

.

[Konstantinos]

I didnt expect that it would change so much the form of the graph.Thanks a lot for the clarification and your solution!

[Star Strider]

As always, my pleasure!