Infrared seekers using reticles with a single detector have been widely used due to small size and low cost. However, the analysis of the error signals and the performance in multiple targets are performed either simplistically or not at all. In this paper, we present detector signals and processing results using image and signal processing techniques, especially performance analysis in multiple targets. The simulation results are essential to make the advanced signal processing part of retical seekers which can deal with various engagement scenarios.