A1: please check if the structure material has loss. Normal incidence and oblique have different losses. It may also mean the simulation time not long enough or autoshutoff min is not small enough. Please refer Ansys Insight: 为什么说仿真时间要足够长才能得到正确的频域结果
A2: PML performance can be degraded as the incident angle or scattering angle is large. So you may need to use different type of PMLs, or use different number of layers. It can be difficult to use one PML for normal incidence to 80 deg. In particular, 80 deg is quite large for most PML settings. You are right that at very large incident angle the simulation time can be very long, due to its inherent limitation of this method. When I wrote that article, I did some tests.
A3: if you only have a few of wavelengths, using Bloch+ single wavelength might be a better choice. You can sweep those wavelengths.
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