Directivity of a grating antenna
I would like to find the directivity pattern of a grating antenna. I have found the far field in 2D and 3D using the scrips farfield2d and farfield3D. But, I would like to apply the "directivity" analysis group in the antenna and find the directivity pattern. I have read the example with the Rectangular Probe Antenna and far field directivity calculations of an antenna and I would like to do the same with my antenna.
Here I present you the farfield2D
Below you can see the design with the directivity analysis group
At the analysis tab you ca see the resolution phi and resolution theta
At the results view, after I click right to calculate the directivity, then I visualized the results. At the visualizer, I plot the polar plot of the directivity and the plot gives me the possibility to change the theta value (phi value can not be changed). I can see that the theta value range is, from 0 to π. I was expecting to plot the directivity which should have a specific theta. If I am not mistaken, the antenna can't have many directivity patterns for different theta values, only just one pattern. The theta value is supposed to be just one value for a specific antenna. Below I show you the results for two different values of theta.
How can I find the correct directivity pattern of the grating antenna? Your advice will be valuable.