A proximity sensor measures the distance of a target and a method operates the proximity sensor. The proximity sensor emits a transmission signal as a free-field transmission wave, which is reflected at the target and as a free-field reflection signal is received by the proximity sensor as a reflection signal, wherein the determining of the distance is provided from the phasing of the reflection signal in relation to the phasing of the transmission signal. The proximity sensor shifts the phasing of the transmission signal chronologically.