A bandpass mass filter for broad ion beams based on mass selective radio-frequency acceleration of ions is described. The ions are extracted from a broad beam ion source by a conventional hole two-grid extraction system. The mass separation consists in multiaperture coaxial hole channels formed of seven grids. The dimensions of the channels are calculated. This arrangement is investigated by ion ray tracing and by experimental investigation. Results for mass resolution (M/Delta M), transmission, and beam current density are presented. For nitrogen, argon, and krypton a transmission of 5%, a beam current density of 4 mu A/cm(2), and a mass resolution of 4 are achieved.