Aperture efficiency of chemically etched horns at 93 GHz

The aperture efficiency of monolithic two-dimensional horn imaging arrays has been optimized at 93 GHz. The imaging arrays consist of several silicon wafers into which arrays of pyramidal horns are etched chemically. Dipole antennas and detectors are suspended on thin silicon oxynitride membranes on one of the central silicon wafers about halfway down the horns. The devices are 7×7 arrays with a 1 λ opening and a 71° flare angle. Antenna impedances have been measured on a low-frequency model. A variety of millimeter-wave dipole antennas and bolometers have been designed and tested. A large-area bismuth thin-film power meter is used to obtain accurate absolute power. The measured aperture efficiency improved from 44% to 72%. The highest system coupling efficiency with a lens was 36% including lens absorption and reflection losses.