August 30, 2023 at 6:32 pm
Guilin Sun
Ansys Employee

You are completely correct and it is expected. Please check this article: https://optics.ansys.com/hc/en-us/articles/360034917253-Solving-bent-waveguides-in-FDE-and-FEEM

Basically, it calculates the angular propagation constant and converts it to the linear porpagation constant:

while the angular "beta" is constant, the radius ca be arbirary. Therefore, you will need to correct the result using 

neff1*R1=neff2*R2

then the result will be constant when you change the bent center and bending radius. Please try and let me know if you have question.