Wideband Windows for Millimeter- and Submillimeter-Wave Vacuum Devices

We present the results of a theoretical calculation and an experimental study of double-sided antireflective processing of a dielectric plate by creating a specially profiled corrugated structure on its surface. Such a structure allows one to minimize the reflection coefficient of an electromagnetic wave to a level of about −30 dB within a range of at least one octave. This antireflective effect can be used in energy output windows of frequency-tunable generators operated in the millimeter- and submillimeter-wave bands. It can also be applied in windows of wideband spectroscopy devices used to diagnose a broad range of materials including both gases and condensed media, as well as in medical devices, in which the studied sample/object is placed in a vacuum-tight box. Theoretical calculations are based on solving numerically the complete equations of the electromagnetic field. Reflections from double-sided corrugated plates were studied experimentally using a Michelson interferometer. It is shown that the reflection coefficient is equal to no more than −23 dB in the 50–220 GHz frequency range. The antireflective profile was manufactured using a plate of radiation-processed fluorine F-4 (Raflon). This new material allowed us to manufacture an antireflective structure with a required accuracy.