Low-noise submillimeter receivers using single-diode harmonic mixers
Article Abstract:
Heterodyne receiver systems include a local oscillator chosen at a frequency adjacent to a signal to be down-converted to an intermediate frequency in a process called fundamental mixing. Signals can be mixed at higher frequencies where local oscillators are not available with the second or higher harmonic of a lower frequency; the desired harmonic is generated within the mixer itself. This harmonic mixing occurs in most mixers whether desired or not. Harmonic mixers differ from fundamental mixers in the degree of importance given to the higher order mixing terms. Single-diode harmonic mixers are simpler, but they do not achieve an optimum set of embedding impedances at the local oscillator and signal frequencies. Submillimeter second- and third-harmonic mixers using a single Schottky diode to determine the optimum local oscillator and signal impedance are studied. Second-harmonic mixers for 490-670 GHz are constructed that largely agree with the theory; they compare favorably with fundamental mixers at the same frequencies.
Publication Name: Proceedings of the IEEE
Subject: Electronics
ISSN: 0018-9219
Year: 1992
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Submillimeter astronomy
Article Abstract:
Aspects of submillimeter-wave astronomy relevant to heterodyne spectroscopy are reviewed. The focus is on the dense interstellar medium in which stars are forming. Submillimeter-wave astronomy depends on extremely sensitive receivers, large accurate telescopes, and high-mountain, airborne, or space platforms. Line surveys of heavy molecule spectra are presented that extend from millimeter wavelengths well into the submillimeter; also provided are examples of light molecule spectroscopy and atomic fine-structure spectroscopy. The gas cooling process allows clouds to collapse to form stars through the submillimeter line emission, particularly from water and diatomic hydride molecules. Regions suffering shocks, photodissociation regions, and stellar outflow regions are also discussed, and a brief description is provided of work on the submillimeter spectrum of nearby galaxies.
Publication Name: Proceedings of the IEEE
Subject: Electronics
ISSN: 0018-9219
Year: 1992
User Contributions:
Comment about this article or add new information about this topic:
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