# Individual Phase plot looks different than the Bode plot

My transfer function is

with Omega_n = 1000.8 and Lambda = .5004 and k = 3

But when I try to individually plot the phase I get something like this

I believe my equation for finding the Phase using ArcTan function is right. Does anyone know why my individual phase plot does not look like phase plot in BodePlot?

• For starters the x axis in the upper plots is logarithmic. Try using a log axis on your plot and see if it becomes identical. – John D Sep 20 '16 at 14:37
• You should use something like atan2 which is inverse tangent but not restricted to -90 to 90 degrees as the one you used. ;) – carloc Sep 20 '16 at 14:41
• Don't know which language you are using, but in some there is a arctan2, which unwinds the angles, so that they are not constraint between -90 and 90 degree. – Arsenal Sep 20 '16 at 14:42
• As the others have said, atan2() is the four quadrant version of atan(). What you're seeing is the wrapping, that is, if the phase will vary more than +/-90deg the output will "reset the counter". As can be seen in the phase graph, your min/max are +/-90deg (+/-pi/2). atan2() will wrap it around +/-180deg. For more, you'll need to unwrap the phase. For your simple experiment, I'd suggest using LTspice with a Laplace expression, in an .AC analysis. – a concerned citizen Sep 20 '16 at 17:20
• I'm voting to close this question as off-topic because it's about maths primarily and how to use the correct tan function in excel. – Andy aka Jul 7 '17 at 6:54