Directivity of Circular parasitic Arrays

Hey,

Could you please help me how to go about getting dirictivity of Circular parasitic Arrays (elements:half-wave dipoles). I am bit confused. The value that i get in my Matlab code is not comparable at all with the one from WILP-D which is the commercial software I am using for reference and cheeking myself.

The approach i used took the normal Directivity expression then let (theta=90deg....theta is elevation angle). I just want to explore beam steering in along Horizontal plane. Thanks!