<< Graphics`Graphics`

dB[z_] = 20 Log[10, Abs[z]];      

    dg[z_] = Im[Log[z]]/Degree;

example 6.10   2nd LPF  p.113

gs = ωn^2/(s^2 + 
              2 ζ ωn s + ωn^2 ) /. {ωn ->  1, ζ ->  0.1}
gω = gs /. s ->  I ω

LogLinearPlot[{ dB[gω], dg[gω] 40/180}, {ω, 0.1, 
        10}, PlotRange -> {{0.1, 10}, {-40, 20}}, 
      PlotStyle -> {Hue[0.9], Hue[0.7]}, GridLines -> Automatic, 
      PlotPoints ->  1000]

ωtab = {0, 0.6, 0.8, 0.9, 0.95, 0.975, 1.0, 1.025, 1.05, 1.1, 
          1.2, 1.4};
nω = Length[ωtab]

p10 = 
        Table[{Re[gω], 
              Im[gω],  ω} /. ω ->  ωtab[[i]], {i, nω}];

zu1 = 
      ParametricPlot[{Re[gω], Im[gω]}, {ω, 0.1, 10}, 
        PlotRange ->  {{-4, 4}, {-6, 2}}, 
        PlotStyle ->  Hue[0.9], 
        AspectRatio ->  Automatic]
zu2 = LabeledListPlot[p10]
Show[zu1, zu2]