A wideband lag correlator for heterodyne spectroscopy of broad astronomical and atmospheric spectral lines

Abstract

WASP2 is a lag correlation spectrometer that is optimized for astronomical heterodyne observations of spectral lines from mid-infrared through centimeter wavelengths. Since the instrument is a wideband microwave spectrum analyzer, its basic technology is well suited to radio astronomy, atmospheric remote sensing, and any other application which requires observations of broad spectral lines. In this specific instrument, eight 16 lag correlator boards form a 128 lag spectrometer with 33 MHz spectral resolution. The spectrometer’s present microwave components dominate its gain shape, yielding a spectrometer which covers a useful (6 dB bandwidth) single band of 3600 MHz, from 280 to 3880 MHz. The correlator boards have a 3 dB bandwidth of 4000 MHz, from below 100 MHz to near their aliasing limit of 4200 MHz. WASP2 obtains its wide bandwidth with fully analog high frequency components: the voltage multipliers are transistor circuits and the delays are lengths of microstrip transmission line. WASP2 is simple, compact, requires little power, and integrates stably for many hours.