Development of multi-beam Fourier phase grating at 660 GHz

Fourier phase gratings play a vital role in the multi-beam heterodyne receiver in sub-millimeter astronomical instruments. In this study, a 1×4 beam grating at 660 GHz is developed, by which the surface structure is generated with an iterative algorithm. Far-field beam pattern is simulated with FEKO, where a relative high efficiency of 91% as well as a uniformity of power distribution among 4 beams of less than 1% are obtained. The grating was manufactured in aluminum material by a micro-milling machine. A PC-controlled scanning stage is employed for the beam pattern measurement. Despite the discrepancy from the manufacture of less than 6 μm, measurement results exhibit a good agreement with simulation in both power efficiency and far-field spatial distribution.