Low-noise heterodyne receivers for near-millimeter-wave radio astronomy

Increased interest in the near-millimeter wavelength region, covering the range 3 mm to 300 µm, during the past decade has stimulated the development of sensitive heterodyne receivers for a wide range of applications. This review paper considers current low-noise receiver technology with emphasis on applications in radio astronomy. A brief discussion of the astrophysical importance of radio astronomy at millimeter wavelengths is presented. The concepts of receiver design and the particular problems associated with this region of the spectrum are discussed. The optimization of material parameters and device topology for both Schottky-barrier diodes and superconducting mixer elements is considered. The extension of waveguide mixer technology into the submillimeter region and the development of quasi-optical receivers is reviewed. Consideration is given to the recent development of efficient harmonic generators for local oscillator (LO) applications at near-millimeter wavelengths.