Dual arc coupler


I want to simulate a coupler made of two bent waveguides, with relatively large radius of curvature (pic attached), and want to calculate the transmitted/coupled power. I have made the model using EME by modifying the directional coupler comprised with straight waveguides. However, the power monitor shows that the power somehow doesn’t propagate beyond 1mm. Where is it going wrong? I am not sure if varFDTD would be useful for the same model considering the structure extends in mm scale, and we cannot characterize the structure with a constant coupling coefficient.
Please advise.double arc coupler Support20181207.lms (3.8 MB)