[IEEE MMET Conference Proceedings. 1998 International Conference on Mathematical Methods in Electromagnetic Theory. MMET 98 - Kharkov, Ukraine (2-5 June 1998)] MMET Conference Proceedings. 1998 International Conference on Mathematical Methods in Electromagnetic Theory. MMET 98 (Cat. No.98EX114) - Low-frequency asymptotics in the diffraction of waves by echelette