Draw polar curves

How can I draw two-fold polar circles? as illustrated in the link http://i39.tinypic.com/5peibo.png

[Mohamed]

I only could draw three-fold polar circles and four-fold polar circles as you can see in these figures http://i40.tinypic.com/21e2o21.png and http://i40.tinypic.com/wv33sx.jpg

Thank you in advance

Answer 1

[Paulo Silva]

t=0:0.01:2*pi;
polar(t,abs(sin(t/2).*cos(t/2)));