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Reflectarray designs at infrared (IR) frequencies are investigated in this paper. At the short-wavelength region, material loss becomes an important consideration in reflectarray designs. Based on the measured properties of conductors and dielectrics at infrared frequency, this paper investigates the loss effects on the reflection magnitude and phase of reflectarray elements. It is revealed that when the material loss exceeds a certain limit, the element reflection phase will vary within a narrow phase range instead of a full 360° phase range. An equivalent circuit model is used to understand this phenomenon. Based on the investigation, alternative design methods for infrared reflectarrays are suggested to lower the loss effect. The low loss reflectarrays have great potential for infrared and visible range applications, such as a low profile planar concentrator for solar energy systems.