The Auger Engineering Radio Array (AERA) is designed to study the radio emissions from extensive air showers at the Pierre Auger Observatory. The array currently consists of a grid of 23 autonomous radio detector stations that measure the radio emissions from cosmic-ray-induced air showers since April 2011. The array is still under construction and is planned to be extended to 160 stations. The new detection technique provides an augmentation of the existing detectors, improves the sensitivity of the observatory and sheds new light on the shower physics. An analysis of the emission processes based on the polarization of the radio pulses is presented.