Progress Toward Corrugated Feed Horn Arrays in Silicon

We are developing monolithic arrays of corrugated feed horns fabricated in silicon for dual‐polarization single‐mode operation at 90, 145 and 220 GHz. The arrays consist of hundreds of platelet feed horns assembled from gold‐coated stacks of micro‐machined silicon wafers. As a first step, Au‐coated Si waveguides with a circular, corrugated cross section were fabricated; their attenuation was measured to be less than 0.15 dB/cm from 80 to 110 GHz at room temperature. To ease the manufacture of horn arrays, electrolytic deposition of Au on degenerate Si without a metal seed layer was demonstrated. An apparatus for measuring the radiation pattern, optical efficiency, and spectral band‐pass of prototype horns is described. Feed horn arrays made of silicon may find use in measurements of the polarization anisotropy of the cosmic microwave background radiation.