12 and to receive the echo wave due to reflection at the surface the transmitted electromagnetic wave is produced by a transmission circuit 16 the output of which is connected to both a frequency mixer 18 and to a circulator 19 to which the antenna 14 is connected the frequency mixer 18 is further connected to the circulator 19 and to a reception and evaluation circuit 20 which determines from the transmission signal applied to the antenna 14 by the transmission circuit 16 and from the reception signals furnished by the antenna 14 the distance e between the antenna 14 and the surface of the material 12 since the distance d of the antenna 14 from the bottom of the container 10 is known the difference between this distance d and the measured distance e produces the wanted material level h to achieve low noise reflections relatively short waves need to be used which are in the microwave range the antenna 14 is naturally designed for transmitting and receiving such short waves it being equipped for example with a horn radiator as is indicated in fig1 for the measurement of the distance e any known radar method may be employed all such methods are based on the principle that the transit time of the electromagnetic waves from the antenna to the reflecting surface and back to the antenna again is measured since the speed of propagation of the electromagnetic waves is known it is possible to.