This gaseous elementary-particle detector is equipped with a readout plate comprising: conductive tiles (80) that are all identical to one another and all located at the same distance from an exterior face (39), these conductive tiles being distributed over the front face of a dielectric layer (72) and being mechanically separated from one another by a dielectric material (76), the smallest dimension of each tile being larger than 300 μm, and electrical connections (88), which are located under the dielectric layer (72) and which electrically connect the conductive tiles in series so as to form conductive strips, these electrical connections being arranged so that each conductive tile belongs to a single conductive strip and each side of one tile is adjacent to the side of another tile belonging to another conductive strip.