Fourier gratings as submillimeter beam splitters

Over the past years, a number of groups have developed phase gratings as local oscillator beam multiplexers for array receivers in the submillimeter wavelength domain. The most popular type of grating is the Dammann (1977) grating, a simple and versatile binary phase grating. We introduce a new type of grating, the Fourier grating, which, in contrast to the binary structure of Dammann gratings, uses a smooth grating structure. Due to the lack of sharp edges these gratings can be manufactured with high precision as reflection gratings even for two-dimensional (2-D) dispersion. Fourier gratings are designed using a simple optimization procedure that only involves a small number of parameters. Their diffraction efficiency is very high. We have produced a number of gratings and tested them at a frequency of 490 GHz, verifying the theoretical results