Abstract :
The purpose of this paper is to discuss key topics related to low-noise mixers, high efficiency multipliers, the use of quasi-optical techniques to reduce circuit losses, and the development of very high-Q devices applicable to the millimeter and submillimeter wavelengths [1]-[5]. In particular, we will describe the development of a highly reliable metalized GaAs Ta-Schottky-barrier diode with native-oxide passivation. The zero-bias cutoff frequency of these diodes is greater than 1000 GHz when measured accurately near 60 GHz with a zero-bias junction capacitance near 0.1 pF. This zero-bias cutoff frequency is approximately twice the value for a comparable nonmetallized device. Using these very high-Q devices, we have achieved RF performance that has advanced prior state of the art. In frequency multipliers, doublers (100-200 GHz), and triplers (100-300 GHz), we have realized conversion efficiencies of 12 and 2 percent, respectively. The CW output power of the doubler was 18 mW and that of the tripler 2 mW. In an image-enhanced mixer at 35 GHz with an IF of 1 GHz, we have realized conversion loss below 3 dB including 0.6-dB circuit losses, and less than 5.9-dB noise figure (SSB) including a 2-dB IF noise-figure contribution.
