How to plot the magnitude and phase of this Fourier Transform frequency response that contains jw?

I have a frequency response X1 = ((j.*w+100).*(j.*w+200))./((j.*w+10).*(j.*w+1000).*(j.*w+10000)); and would like to plot its magnitude in dB and phase versus the log of frequency with frequency from 0.5Hz to 3000Hz in steps of 5Hz but it doesn't seem to work because of the 'j' in my function.

This is my code:

clf % Clear any existing figure

w = log(0.5):log(5):log(3000); % Frequency from 0.5Hz to 3000Hz with increment of 5Hz

X1 = ((j.*w+100).*(j.*w+200))./((j.*w+10).*(j.*w+1000).*(j.*w+10000)); % Blue

subplot(2,1,1)

plot(w,abs(X1));

title('Magnitude')

ylabel('Magnitude (db)')

xlabel('Log of Frequency')

ylim([-1 10]);

grid on

subplot(2,1,2)

plot(w,angle(X1));

title('Phase')

ylabel('Phase (°)')

xlabel('Log of Frequency')

grid on

Answer 1

[Star Strider]

If you define ‘w’ differently, and change (or delete) the ‘ylim’ assignment, you can see it.

I defer to you to determine if it does what you want.

w = logspace(-3,4);

X1 = ((j.*w+100).*(j.*w+200))./((j.*w+10).*(j.*w+1000).*(j.*w+10000)); % Blue

subplot(2,1,1)
semilogx(w,20*log10(abs(X1)));
title('Magnitude')
ylabel('Magnitude (dB)')
xlabel('Log of Frequency')
set(gca, 'XLim',[0.5 3000])
% ylim([-1 10]);
grid on

subplot(2,1,2)
semilogx(w,angle(X1)*180/pi);
title('Phase')
ylabel('Phase (°)')
xlabel('Log of Frequency')
set(gca, 'XLim',[0.5 3000])
grid on

I added the conversion to dB in the magnitude plot, and the conversion from radians to degrees in the phase plot, since you apparently want those.