For example if I have the following transfer function:
$$H(s) = \frac{1}{\cosh(\sqrt{s/10})}$$
Can I do the bode plot it in matlab or do I need to rationalize it beforehand?
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$\begingroup$ What have you tried? $\endgroup$– MBazCommented Feb 7, 2023 at 23:02
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$\begingroup$ I was looking into irrational transfer functions , and I could not find any refrence. I have not tried anything since I have no idea where to start $\endgroup$– FISqrtCommented Feb 7, 2023 at 23:05
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$\begingroup$ The Bode plot is the magnitude and phase of H(s) as you limit s to be the $j\omega$ axis. So as long as you can compute a magnitude and phase of the function, you can plot it! $\endgroup$– Dan BoschenCommented Feb 7, 2023 at 23:59
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2 Answers
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If that's a problem for you, I recommend taking a basic Matlab class first.
%% plot a transfer function
% frequency axis
omega = logspace(-2,2,1000)';
% calculate the trasnfer function
H = 1./cosh(sqrt(1i*omega/10));
% and plot it
clf;
subplot(2,1,1);
semilogx(omega,10*log10(H.*conj(H)));
grid on;
ylabel('Level in dB');
xlabel('Frequency in Rad/sec');
subplot(2,1,2);
semilogx(omega,unwrap(angle(H)));
grid on;
ylabel('Phase in rad');
xlabel('Frequency in Rad/sec');
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$\begingroup$ Expressing frequencies in Hz and angles in degrees is left as an exercise to the reader. $\endgroup$ Commented Feb 8, 2023 at 15:37
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$\begingroup$ @TimWescott or incurs an additional charge of $3.99 plus tax and tip. :-) $\endgroup$– HilmarCommented Feb 9, 2023 at 8:13
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Matlab's bode function is just a wrapper for calculating a system response and then graphing it.
So, just do that by hand.
