Try this:
t = 0 : 2*pi/177 : 2*pi;
a=linspace(0.3,0.5,178);
m=linspace(0.4,0.6,178);
figure(3)
ax = polaraxes;
hold on
polarplot(ax,t,a,'-b')
polarplot(ax,t,m,'-r')
ax.RColor ='blue';
ax.ThetaDir = 'counterclockwise';
ax.ThetaZeroLocation = 'bottom';
thetaticks([0:30:360])
thetaticklabels({'180','150','120','90','60','30','0','330','300','270','240','210'})
rlbl = sprintfc('%.0f',(0:2:6)); % Radius Labels
text(ones(1,4)*1.8*pi, (0:2:6)*0.1, rlbl, 'Color','r') % Label Radii
addgrid = [0.1; 0.3; 0.5]*ones(size(t)); % Calculate Grid Lines At [0.1 0.3 0.5]
polarplot(ax, t, addgrid, '--k') % Plot Them
Experiment to get the result you want.
