For making the electro-optical modulator which can generate ultra wide sideband spectrum

a kind of stripline electrode with complex pattern was proposed. So we present a numerical method which combines Planar Waveguide Model Method and Boundary Element Method to determine the resonant frequencies of the kind of electrode in wide frequency band width of microwave. And we use Gaussian integrating formula to get the solution of a derived boundary integral equation .The calculating result approximately corresponds to the experimental result.