Dielectric Layer Loss
The dielectric layer loss calculations in Sonnet are virtually exact. Our web site has a lossy conductivity benchmark you can perform on any electromagnetic solver (or measurement system). See benchmarking on the Products section of our web site, https://www.sonnetsoftware.com/benchmarking.
The dielectric loss is calculated in Sonnet at the beginning stages of the analysis. The method Sonnet uses starts with the calculation of a sum of waveguide modes. The exact solution requires an infinite sum of modes, but Sonnet truncates this sum to some reasonable value (the truncation has never been a source of error). For each mode, if there is a lossy dielectric, the calculation involves complex numbers instead of just real numbers. This is NOT a discretized function - it is a continuous function. Therefore, the dielectric loss calculation can be thought of as exact (only limited to the precision of the machine).