Reply To: Help regarding the simulation domain , monitor dimensions

[Dimitris Polyzos]

Hello Prabha,

I would be interested to see your simulation model as I am not absolutely sure if you have set correctly the FDTD span and the monitors. However, I believe that the transmitted fields correspond to scattered fields, then I reckon that you should place the monitor close to the source. From size perspective, monitors should be large enough in order not to "cut " the transmitted fields. If that is not applied, then the transmission will not be correct. For the same reason you should position the monitor fairly close to the structure. Actually, the further away the monitor is, the wider it should be to encompass the diffracted fields without truncating them. I would set the monitor to be as large as the FDTD region.
For the source, I don't think it really matters, as long as it is big enough to includes the full aperture. So the following things should be considered regarding the accuracy of the far field projections:

• the accuracy of the FDTD calculation itself (mesh)
• the field truncation at the edge of the monitor/simulation region

Lastly, make sure the FDTD region is big enough: if the PMLs are too close to the aperture, they may affect the evanescent fields. Half of the larger wavelength of interest is usually a good starting point, but you may want to validate this by varying the size of the FDTD region and see how it affects the results. Please refer to the following articles:

 Integrating power in far field projections

farfieldfilter - Script command

 Using spatial filtering to avoid truncating fields in far field projections

I hope I helped.

Kind regards

Dimitris