A monolithic two-dimensional horn imaging array has been fabricated for millimeter wavelengths. In this configuration, a dipole is suspended in an etched pyramidal cavity on a 1- mu m silicon-oxynitride membrane. This approach leaves room for low-frequency connections and processing electronics. The theoretical pattern is calculated by approximating the horn structure by a cascade of rectangular-waveguide sections. The boundary conditions are matched at each of the waveguide sections and at the aperture of the horn. Patterns at 93 and 242 GHz agree well with theory. Horn aperture efficiencies of 44+or-4%, including mismatch and resistive losses, have been measured. A detailed breakdown of the losses is presented. The coupling efficiency to various f-number imaging systems is investigated, and a coupling efficiency of 24% for an f0.7 imaging system (including spillover, taper, mismatch and resistive losses) has been measured. Possible application areas include imaging arrays for remote sensing, plasma diagnostics, radiometry and superconducting tunnel-junction receivers for radio astronomy.
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