A new technique which combinesthe generalized network formulation along with theboundary integral method and the connection algo-rithm is proposed to deal with the electromagneticcharacterization of the transmission and scatteringproperties of a complex 3-D (three-dimensional) slotin a thick conducting plane.First,the interior cav-ity of the slot is divided into sections according to itsconfiguration and filling characteristics and the gener-alized admittance matrix of each section is computedby the boundary integral method.Using the connec-tion algorithm,the interior admittance matrix of theoverall slot can be derived by cascading the admit-tance matrices of individual sections.Then the aper-ture equivalent magnetic currents,the backscatteredfield and the transmitted field can be obtained by thegeneralized network formulation.Numerical examplesare presented to demonstrate the validity,versatilityand capability of the technique.The technique can beused to not only efficiently handle arbitrary slot re-gardless of its geometry and material properties butalso greatly reduce the memory requirement and com-putation time.