hfss scattering of plate

Hello everyone,

I don't know if someone can help me on this.
I am trying to solve a simple scattering problem from a PEC (perfect electric conductor) rectangular plate.

I have an incident field, and I also have prepared a boundary condition on the plate (Rad1). Also I have completed the near and far field sphere setups.

I analyze and solve the problem, but the plot of magnitude (Etotal) with angle of observation (theta which varies from 1 to 89 degrees) doesn't give me a sinc function result, as expected...

Any ideas?
I have attached the file.