Abstract
A 4-f imaging system was used for collecting images of complex thermal radiation Moiré patterns that were processed using the coherent illumination-direction-multiplexing Fourier Ptychographic imaging algorithm. We show that the observed Moiré patterns can be explained by assuming the sample was simultaneously illuminated from different directions by several thermal radiation beams coherent with each other. Our results revealed that the numerical algorithm was stable when the phase of the optical disturbance at the sample's plane was known, but it failed to determine the correct phase when it is unknown.