The shielded rectangular cross section slab line with cylindrical inner conductors is of great importance to microwave engineering and design.In this paper,boundary element method(BEM) is applied to calculating the characteristic impedance of the shielded rectangular line with multi cylindrical inner conductors.The computational formulations of the self capacitance and coupling capacitance is derived.The accuracy of the impedance data is confirmed by comparing the numerical results reported in the litera...