w = linspace(0.001,pi,1000);
G = tf(0.001987*[1 0.9931],conv([1 -1],[1 -0.9802]),-1);
GGc = tf(0.001987*[1 0.9931]*(1-0.8)/(1-0.9802),...
           conv([1 -1],[1 -0.8]),-1);
bode(G,'-',GGc,'--',w), grid