How to see the plot for theta = 90 to 180 for 3d far field projection?

- November 9, 2021 at 1:04 pm
  
  nafis16buet
  Subscriber
  
  Hello,
  I have a confusion about far field projection visualized from DFT monitor.
  As we can see in the image below, far field projection is plotted with respect to phi(0 degree to 360 degree) and theta (0 to 90 degree). But we know that for spherical coordinate system, theta runs from 0 to 180 degrees. So, how do we view the data or plot for theta ranging from 90 to 180 degrees?
- November 9, 2021 at 4:30 pm
  
  Guilin Sun
  Ansys Employee
  
  This is a good question. Please first refer this article: https://support.lumerical.com/hc/en-us/articles/360034394294-Understanding-direction-unit-vector-coordinates-in-far-field-projections
  Usually we have a plane monitor, so the far field is only on half sphere, thus theta is from 0 to 90, 2pi space.
  The far field graph does not label theta larger than 90, due to visual betterness.
  90 to 180 will be the backward propagation, which is very small due to PML reflection and source injection error.
  in short, a plane monitor can only give its farfield in half sphere. and we cannot compress the sphere like world map to view the farfield in 4pi space, as it introduces distortion.
- November 10, 2021 at 3:15 pm
  
  nafis16buet
  Subscriber
  
  Excellent answer. That was really helpful, . I was wondering if I could visualize the hemispherical surface where far field is calculated, just as in your shared link. Is this possible?
- November 10, 2021 at 4:42 pm
  
  Guilin Sun
  Ansys Employee
  
  Currently no, but you can modify the dataset to be finite element then you can use "surface" in visualizer. https ://support.lumerical.com/hc/en-us/articles/1500006340081-Creating-a-far-field-radiation-plot-from-FDTD-angular-distributions
  or you can directly use DGTD which is FEM method.
- November 10, 2021 at 5:33 pm
  
  nafis16buet
  Subscriber
  
  Thanks again.