Approximate analytical boundary conditions for efficient finite difference frequency domain simulations in cylindrical coordinates

A simple technique of numerical analysis of open resonator is presented. The technique combines a standard Finite Difference method with the Partial Eigenfunction Expansion. By doing this one gets a simple formulation of radiation boundary condition. The algorithm was tested for the dielectric resonator of different height placed in infinite radial waveguide and excellent agreement of the obtained results with other methods was achieved.