Coupling impedance of a periodic array of diaphragms

The method is presented for calculating the high-frequency longitudinal transverse coupling impedances in a periodic array of diaphragms in a circular perfectly conducting pipe. The method is based on Weinstein´s theory of diffraction of a plane electromagnetic wave on a stack of halfplanes. Using Weinstein´s solution, it is shown that the problem of finding the beam field in the pipe reduces to an effective boundary condition at the radius of the diaphragms which couples the longitudinal electric field with the azimuthal magnetic one. Solving Maxwell´s equations with this boundary condition leads to simple formulae for Z_long and Z_tr. A good agreement with a numerical solution of the problem found by other authors is demonstrated