Adjust the phase offset when using data from 'bode'

Romain Liechti · Mar 23, 2022 · 2.4K views
Question
I'm trying to look at the phase and gain margin of an openloop system. Due to presentation/publications, I had to designa function to plot my amplitude and phase response with good font, font dimensions etc. To do so, I'm using the bode function to extract the data from my state space systems. But I have a problem with a phase offset (value at 0Hz). I know we can remove it from the properties editor avalaible in the classical bode plot but is there a solution to correct it when using this syntax [mag,phase,wout] = bode(sys,w) ?
Expert Answer
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Neeta Dsouza PhD Expert
Answered Aug 25, 2026

if you want - as you write - stick to the bode output you should correct the phase by a reference phase shift.

 

% create tf
sys = tf(1,[1 0]);

% calculate frequency response using bode
w = 2*pi*logspace(log10(0.1),log10(1e5),1000);
[mag,phase,wout] = bode(sys,w);

mag = squeeze(mag);
phase = squeeze(phase);

% correct phase
w_ref = 2*pi*1; % reference is 1 Hz here, 0 works as well for DC
[~,corrPhase,~] = bode(sys,w_ref);

phase = phase-corrPhase;

 

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