grating lob condition not working

[yefj]

Hello i have build an antenna array shown bellow.our main beam is at 180 degrease
the frequency is 10Ghz.i have exiced then all the same amplitude with no phase.
lambda=30mm theta_0=0 d=48mm
48/30=1/(sin(theta)-sin(theta_0))
theta_0=0
theta=38.68
180+38.68=218
180-38.68=141
So i know that my grating lobes are rising because d/lambda>1 but grating lobe supposed to be in the same amplitude as the main lobe.
why they are smaller the the main lobe?
Thanks.

 

[Geralt_of_Rivia]

Grating lobes have the same amplitude as the main lobe when you are calculating the Array Factor. But when you are calculating the radiation pattern, the effect of element factor causes the pattern to have grating lobes with lower amplitude levels.