An arrangement for measuring fill level of a fill substance in a container, comprising: a fill level measuring device, wherein the device includes measuring device electronics and an antenna connected to the measuring device electronics; and at least one feedthrough installed in a signal path of the microwave signals or the reflection signals; the feedthrough. The feedthrough comprises a hollow conductor, into which a microwave transparent window is inserted gas tightly. The window comprises: a disk, whose thickness corresponds approximately to a half wavelength or a small integer multiple of the half wavelength of a first, hollow conductor propagation capable, signal mode of the microwave signals at a predetermined signal frequency in the disk; and two matching layers located on oppositely lying, outer surfaces of the disk. The thickness of each matching layer corresponds approximately to a fourth of the wavelength of the first, hollow conductor propagation capable, signal mode of the microwave signals at the predetermined signal frequency in the matching layers.