Abstract: Device for estimating, at high temperature, the electromagnetic properties of a material, including:an oven (1, 19, 20);a waveguide (3) disposed at least in part in said oven, a housing for a specimen piece of uniform thickness made of said material, this specimen piece being such that, when it is disposed in said housing, its outer periphery matches the inner surface of the waveguide;means (4, 5, 6) for applying an incident very high frequency electromagnetic wave to the waveguide (3); andmeans (4, 5, 6) for collecting the electromagnetic wave reflected by said specimen piece.A vertically disposed waveguide has (3) said housing provided at the open lower end (3B ).