The invention relates to an intrinsic-
analysis method for assigned frequency of a periodic structure, which includes steps: A, setting a
functional equation which can consider boundary value of an
electromagnetic field in conductors and medium loss periodic structure and can obtain the boundary value of the
electromagnetic field by means of standard variation principle of the
finite element method; B, solving solution domain by gridding
subdivision of a
tetrahedron and guaranteeing gridding matching of a primary side and a
secondary side of the periodic boundary; C, selecting primary function, expanding electric-
field intensity vector in all grids by the primary function and obtaining a matrix equation of expansion coefficient by Ritz method; D, writing the matrix equation of the expansion coefficient into a linear generalized intrinsic equation about
propagation constant; E, solving the linear generalized intrinsic equation by setting a frequency, obtaining attenuation constant and phase constant corresponding to the set frequency according to the
propagation constant, and obtaining interaction impedance through
after treatment; and F, repeating the step of E to obtain attenuation constants, phase constants and interaction impedance corresponding to different frequency.