Using freqs to plot butterworth filter frequency response

I'm attempting to use the Matlab freqs function to plot the frequency response of a first and second order butterworth filter by passing it the corresponding A(s) and B(s) polynomial values for each filter order.

I am having a tough time understanding what is showing up when I plot the magnitude vs frequency. It looks like the chart is mirrored, not like a normal butterworth response should look like, and I can't chase down the cause. Anyone have this issue before?

https://imgur.com/a/AuV5d

Code

    %First Order
    Num1=[0 1];
    Dem1=[1 1]; 
    w = (0 : 100*2*pi/100 : 100*2*pi); %freq range

    T1=freqs(Num1, Dem1, w); %calculate the transfer function

    axis([0 100 -30 0])
    plot(w/(2*pi),20*log10(abs(T1)))

    %Second Order
    Num2=[0 0 1];
    Dem2=[1 1.4142 1]; %repeat for second order

    T2=freqs(Num2, Dem2, w);

    hold on
    plot(w/(2*pi), 20*log10(abs(T2)))
    grid on
    hold off

Answer 1

[Star Strider]

I don’t understand what you mean by ‘mirrored’.

When I used:

w = logspace(-3, 2);

and used semilogx instead of plot, I got what appears to be an acceptable plot for a lowpass filter. The rest of your code is unchanged.