A modified locally conformal Finite-Difference Time-Domain technique (MLC-FDTD) is presented in this paper

which is used to analyze the broadwall radiating slots in a finite wall thickness waveguide

including the longitudinal slot and the compound inclined slot.MLC-FDTD not only removes the instability of the original locally conformal FDTD algorithm

but also improves the computational accuracy by partly modifying E-filed update equations according to the complexity of the slot fringe fields.In this paper

we make a direct analysis of the bulletheaded slots by using MLC-FDTD

and give the equivalent errors of two kinds of equivalent methods frequently used in the engineering design

which are the equal-area and the equal-perimeter transformations from the squareheaded to bulletheaded slot.The result shows that the equal-area transformation is more accurate.