A Compact Heterodyne Millimeter-Wave/Terahertz Spectrometer for Remote Sensing

Abstract

Heterodyne spectroscopy using millimeter-wave/terahertz heterodyne receivers is a very suitable method for remote sensing of gases in space and in the atmospheres of Earth and other planets. Compact and lightweight receivers are essential for applications on small satellites. We have utilized an integrated SiGe BiCMOS receiver front-end with a local oscillator (LO) tunable from 225 GHz to 255 GHz, along with a compact back-end spectrometer based on a digital Fast Fourier Transform Spectrometer (dFFTS) and characterized it for heterodyne spectroscopy. For the front-end, an integrated SiGe BiCMOS receiver with a tunable LO is already available. Previously, we demonstrated gas spectroscopy with a lab-scale dFFTS as a back-end, but that system was not suitable for a compact instrument [1]. In this contribution, we present measurements of the spectra using a newly available compact dFFTS from Pacific MicroCHIP Corp. with dimensions of (11 × 10.5 × 1.5) cm3,a weight of 200 g and a power consumption of 2.5 W. We measured a DSB noise temperature of around 15 000 K and an Allan time of 17 s at an LO frequency of 239.2 GHz and an intermediate frequency around 240 MHz. We also demonstrated that this setup is capable of measuring rotational transitions of acetonitrile ( CH3CN ) around 239 GHz in a laboratory setup. As a next step, we plan to launch this receiver on a compact weather balloon to measure ozone O3 at a frequency of 235.710 GHz in the atmosphere up to an altitude of 40 km.