Space-qualified submillimeter radiometer

Abstract

The purpose of this research was to develop a reliable submillimeter wave spectrometer for space-borne high frequency spectral line work. The emphasis was on improving the efficiency of frequency multipliers to limit the system components to rugged, low power consumption solid-state devices. This research has allowed Millitech to develop increased efficiency and performance in Millitech's existing line of submillimeter components and systems. Millitech has fabricated and tested a complete solid-state spectrometer front end for use at 560 GHz (the 1(sub 10) to 1(sub 01) transition of water vapor). The spectrometer was designed with the rigors of flight conditions in mind. The spectrometer uses a phase-locked, solid-state Gunn diode oscillator as the local oscillator, employing a tripler to produce about 3 mW of power at 285 GHz, and a low noise second harmonic waveguide mixer which requires less than 2 mW of LO power. The LO (and the signal) is injected into the mixer by means of a quasioptical diplexer. The measured system noise temperature is 2800 K (DSB) over 400 MHz. The whole spectrometer front end is compact (21 cm by 21 cm by 24 cm), light (7.4 kg), and has a power consumption of less than 8 W. Other topics explored in this work include compact frequency agile phase lock loops, optical filters, and InP Gunn oscillators for low noise applications. As a result of this research, the improvement in the design of multipliers and harmonic mixers will allow their use as the LO power for a variety of satellite-borne receivers operating in the 200 to 600 GHz frequency range