example 6.8 p. 112

eq = {K == u (1 + wT^2), 
        K wT  ==  v (1 + wT^2)}

Solve[eq, v, wT]

gw = k/(1 + s) /. {k ->  1, s ->  I wT}

ParametricPlot[{Re[gw], Im[gw]}, {wT, 0, 10}, 
      PlotRange ->  Automatic]