Heterodyne spectrometers with very wide bandwidths

Andrew I. Harris

doi:10.1117/12.459150

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17 February 2003 Heterodyne spectrometers with very wide bandwidths

Andrew I. Harris

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Proceedings Volume 4855, Millimeter and Submillimeter Detectors for Astronomy; (2003) https://doi.org/10.1117/12.459150
Event: Astronomical Telescopes and Instrumentation, 2002, Waikoloa, Hawai'i, United States

Abstract

New astronomical and remote-sensing instruments require microwave spectrometers with modest spectral resolution over many gigahertz of instantaneous bandwidth. Applications include millimeter-wave searches for distant objects with poorly known redshifts, submillimeter and far-infrared observations of Doppler-broadened spectral lines from galaxies, and observations of pressure-broadened atmospheric lines. Wide bandwidths and the consequent stability requirements make it difficult to use general-purpose receiver and spectrometer architectures in these applications. We discuss analog auto- and cross-correlation lag spectrometers that are optimized for these observations. Analog correlators obtain their wide bandwidths by a combination of transmission line delays and direct voltage multiplication in transistor or diode mixers. We show results from a new custom transistor multiplier with bandwidth to 25 GHz. Stability becomes increasingly important as bandwidths broaden. We discuss system requirements for single-dish correlation radiometers, which have intrinsic high stability, and present results showing that analog cross-correlators are suitable backends for these receivers.

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Andrew I. Harris "Heterodyne spectrometers with very wide bandwidths", Proc. SPIE 4855, Millimeter and Submillimeter Detectors for Astronomy, (17 February 2003); https://doi.org/10.1117/12.459150

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