A method and apparatus for measuring radiant energy scattering characteristics of a test panel of dielectric material over a circular arc are disclosed. The test panel is supported on a turntable at a position on the axis of the turntable. The turntable has a fist antenna radially mounted thereon for rotation therewith and directed toward the position of the supported test panel. The test panel support is rotated with respect to the turntable to selectively position the test panel at a predetermined incidence angle with respect to the first antenna. The turntable is rotated with respect to a second antenna which is in a fixed stationary position and directed toward the supported position of the test panel to selectively position the test panel at an incidence angle with respect to the axis of propagation of the second antenna that is equal to and opposite the predetermined incidence angle. Radiation transmitted between the first and second antennas is measured with the test panel in the supported position at each of a plurality of predetermined equal and opposite incidence angles with respect to the first and second antennas; and radiation transmitted between the first and second antennas is measured at each of the plurality of predetermined incidence angles when the test panel is not supported on the turntable. The reflectance characteristics of the test panel are then determined by subtracting the measurements taken without the test panel in place from those taken with the test panel supported on the turntable.