---

K = k1*k2*k3;
den = conv([T2 1],[T3^2 2*d*T3 1]);
w = 0.01:0.001:100;
Wjw = K ./ polyval(den, 1i*w);
plot(real(Wjw), imag(Wjw)); grid on
hold on; plot(-1, 0, 'r+'); hold off