How to draw BODE PLOT In MATLAB!

Suppose take a transfer function

G(S) H(S)= 10/(S+1)

To plot a Bode Plot for this Transfer function. 

Open Matlab .
In the command window, write the co-efficients of S^2  and S as well as constant.

Following this rule, we shall write the numerator of G(S) H(S) as num=[0 0 10] , which means numerator only contains a constant i.e 10 .S^2 and S are absent

Coming to the denominator of G(S) H(S)=[0 1 1], which means denominator doesn't contains S^2, and co-efficient of S is 1 and the constant is 1.  

Figure 1

Bode plot of above TF can be drawn in Matlab using matlab command Bode(num,den) as shown above.

Bode Plot :

Figure 2

The transfer function G(S) H(S)=10/S+1 is a Single Pole transfer function.

Here  cutoff Frequency wc=1/(coefficient of S) is 1 rad/sec.

As you all know actual bode plot differs from the approximation bode plot by -3dB as shown below

Figure 3

REFER TO FIGURE 2

 We can see  that, at the cut-off frequency or  at the POLE, the Magnitude plot at the pole location varies by -3dB  i.e (20dB-3dB=17 dB. Hence We can conclude that Matlab gives actual Bode plot.

Feel free to ask any questions. We shall see few more Transfer functions in the next post.