Abstract-In this paper, a calculation method for bore sight error voltage is presented for aperture antennas enclosed in radomes of arbitrary shapes.The method adopts a ray tracing technique frequently used in computer graphics field in constructing two dimensional computer graphics images to obtain a projected image of source distribution, thereby bore sight error voltages and far field radiation patterns are calculated fast and accurately. Besides, the method enables us to use various acceleration schemes used in computer graphics readily. Numerical calculations show that projected source images with a resolution higher than 0.1λ and multiple reflections taken into account produce reliable results. The validity of the method is verified by comparison with results of an analytic solution.