The dual MMW/IR mode for the testing of the modern missile seekers is required. The dual band test system calls for a combining element that can bring both MMW and IR beams to the same seeker head. Optical Holographic technique was used to overcome the fabrication problems associated with the manufacturing of a large size (MMW/IR) beam combiner that should be transparent to MMW while reflecting IR beam. In our previous investigation we designed and produced a surface relief holographic optical element (HOE) that satisfied the beam combiner requirements. Since the uniform metal coating of any meaningful thickness would reflect most of MMW radiation the HOE was partially metalized, so that it became transparent for TM polarized MMW, while maintaining excellent reflectance of IR. To correct the losses in the TE polarized MMW, the lines were 'cut' through the metal coating in the direction perpendicular to the groove structure, creating discontinuities in the metallic coating in both directions. The minimal size of the beam combiner required to perform dual band function with the minimal MMW distortion was calculated.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.