# Bode Plot and Corner Frequency

26 views (last 30 days)
Ethan Johnston on 17 Nov 2022
Commented: Star Strider on 18 Nov 2022
I am trying to figure out how to get the corner frequency to show up on my bode plot or in the command window in matlab but everything i have tried doesn't work or gives me inf. is there any easy way to get the corner frequency (breakpoint) to show on the figure or the command window? here is what i have so far for my code:
w = logspace(-2,4,500);
num1 = [1 1];
den1 = [1];
num2 = [1 2 1];
den2 = [1];
sys1 = tf(num1,den1)
sys1 = s + 1 Continuous-time transfer function.
figure(1)
bode(sys1,w)
grid on
hold on
sys2 = tf(num2, den2)
sys2 = s^2 + 2 s + 1 Continuous-time transfer function.
figure(1)
bode(sys2, w, 'r')
grid on
Ethan Johnston on 17 Nov 2022
My question is how to add markers to the plot of those values. Sorry, I should have been more specific. I don't have any work that I calculated yet for it.

Star Strider on 17 Nov 2022
The ‘sys1’ and ‘sys2’ transfer functions are actually improper, wince with a denominator of 1, they are infinite differentiators.
As such, they have no corner frequencies.
To get the frequencies at any points in the frequency response that you want, use freqresp and interp1
w = logspace(-2,4,500);
num1 = [1 1];
den1 = [1];
num2 = [1 2 1];
den2 = [1];
sys1 = tf(num1,den1)
sys1 = s + 1 Continuous-time transfer function.
figure(1)
bode(sys1,w)
grid on
H1 = freqresp(sys1,w);
H1 = squeeze(H1);
hold on
sys2 = tf(num2, den2)
sys2 = s^2 + 2 s + 1 Continuous-time transfer function.
figure(1)
bode(sys2, w, 'r')
grid on
[H2,wout2] = freqresp(sys2,w);
H2 = squeeze(H2);
It is also possible to calculate where the phase reaches a certain value, however it may be necessary to restrict ‘w’ to a monotonically-increasing or -decreasing part of the spectrum in order to avoid problems with non-unique values.
.
##### 2 CommentsShowHide 1 older comment
Star Strider on 18 Nov 2022
As always, my pleasure!

### Categories

Find more on Time and Frequency Domain Analysis in Help Center and File Exchange

R2021b

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!