alpha=0.9; T=1; alpha0=0.8:-0.1:0.1;
G=tf([alpha*T,1]/alpha,[T,1]);
[x,y,w1]=nyquist(G,{.1,10});  [m,p,w2]=bode(G,{.1,10});
x=x(:); y=y(:); m=m(:); p=p(:);
for i=1:length(alpha0)
   G1=tf([alpha0(i)*T,1]/alpha0(i),[T,1]);
   [xx,yy]=nyquist(G1,w1); [mm,pp]=bode(G1,w2);
   x=[x,xx(:)]; y=[y,yy(:)]; 
   m=[m,mm(:)]; p=[p,pp(:)];
end
subplot(211); semilogx(w2,20*log10(m))
subplot(212); semilogx(w2,p); 
figure, plot([x,x],[y -y]), 
axis([0,10,-5,5]); axis('square')