A new system has been installed on the JET tokamak consisting of six independent fast-sweeping reflectometers covering four bands between 44 and 150 GHz and using orthogonal polarizations. It has been designed to measure density profiles from the plasma edge to the center, launching microwaves through 40 m of oversized corrugated waveguides. It has routinely produced density profiles with a maximum repetition rate of one profile every 15 μs and up to 100,000 profiles per pulse.