Guilin Sun
Ansys Employee

It can be very challenge if you use plane wave source. I do not know where is the location to generate the SPP. You can use mode source to find the SPP mode at the location you know, and check its characteristics.

usually, you can get some information through transmission, eg there is a wavelength that exhibits extraodinary behavior. eg, sharp transmission decline etc.

For non-periodic structure, plane wave will be truncated by PML and create diffraction. Might be better to use Gaussian source.

you will need try different settings and see if the desired phenomenon occurs.  You will need to have a better understanding of SPP mode. You can use mode expansion monitor to check how much the transmission is for this SPP mode. Please read SPP and mode expansion monitor online.