  As part of the ongoing AugerPrime upgrade of the Pierre Auger Observatory, we
are deploying short aperiodic loaded loop antennas measuring radio signals from
extensive air showers in the 30-80 MHz band on each of the 1,660 surface
detector stations. This new Radio Detector of the Observatory allows us to
measure the energy in the electromagnetic cascade of inclined air showers with
zenith angles larger than $\sim 65^\circ$. The water-Cherenkov detectors, in
turn, perform a virtually pure measurement of the muon component of inclined
air showers. The combination of both thus extends the mass-composition
sensitivity of the upgraded Observatory to high zenith angles and therefore
enlarges the sky coverage of mass-sensitive measurements at the highest
energies while at the same time allowing us to cross-check the performance of
the established detectors with an additional measurement technique. In this
contribution, we outline the concept and design of the Radio Detector, report
on its current status and initial results from the first deployed stations, and
illustrate its expected performance with a detailed, end-to-end simulation
study.
