This paper focus on the theory of Connecting Boundary Conditions in FDTD (Finite Difference Time Domain) Calculation, and calculates the incident field by the approach of one dimension FDTD calculation on x axes instead of the analytic method, and applies it to the connecting boundary conditions of two dimensions FDTD calculation. The Object Oriented Programming (OOP) and structural programming thought make setup incident wave easier. At last this paper tests several examples of RCS (Radar Cross Section) calculation and gives out the results and graphs, It is proved that the incident wave leaks is very low and the precision in calculation is high. In comparison with the MOM method,the final results of the two methods are consistent highly.
