An array bolometric detector for detecting an electromagnetic radiation in a predetermined infrared or terahertz wavelength range, including a substrate, and an array of bolometric microplates for the detection of the radiation, suspended above the substrate by support elements. The detector includes a membrane arranged above each microplate, and having patterns having a refractive index smaller than that of the membrane formed therein. The patterns are placed periodically along at least one axis of the membrane, according to a period shorter than or equal to λ n , where λ is a wavelength to be detected and n is the average refractive index of the medium separating the microplate from the membrane. The width of the patterns along the axis increases from a central location of the membrane towards the periphery thereof.