Check these equations for RMSA (directivity)

I'm doing a project about rectagular microstrip antenna using transmission line model. I'm face some problem about the equation to calculate their parameter. I found 2 equation to calculate the directivity.

1. U=[sin(t)sinc(Ko×h×sin(t)×cos(p)/2×pi)sin(Ko×W×cos(t)/2pi)cos(Ko×Leff×
sin(t)sin(p)/2]^2
D=4pi×Umax/Prad

2. D= [2pi×W/λo]^2×pi/I

pi pi
I= ∫∫ [sin(Ko×W×cos(t)/2)/cos(t)]^2×sin3tcos2t(Ko×Leff×sin(t)sin(p)/2 ,
0 0

About the equations, which one is correct. And I'm also confused to calculate the radiation pattern which is a lot of equation too. Anyone can help and guide me.

Thanks in advance.