Validity of approximate boundary conditions for periodic strips on cylindrical substrates

The strip gratings on dielectric cylinders are analyzed by using two types of approximate boundary conditions and by the moment method (MoM). The used approximate boundary conditions are the boundary conditions obtained by the homogenization method (BCHM), where the local planar approximation was applied, and the asymptotic strip boundary conditions (ASBC). The results show that the both approximate boundary conditions give good results when the period of the strips is small compared to the wavelength. However, BCHM gives more accurate results, and practically there is no difference between the MoM results and the results obtained by BCHM method if the periodicity is small enough. Furthermore, the ASBC cannot predict the coupling of the incident wave to the waveguide modes of the strip-loaded dielectric cylinder, which is predicted both by the MoM and the BCHM methods. The numerical results are also compared to measurements showing a very good agreement