Single sideband modulator, a key component of Tore-Supra heterodyne reflectometers

Abstract

Although single sideband modulation offers a simple solution to active heterodyne devices and is common in devices working over 150 GHz, it has been scarcely used for reflectometers. For a few years, large bandwidth (12–20 GHz), high performance single sideband modulators (SSBM) have been available. For higher frequency application, a sideband rejection around −25 dBc seems necessary to ensure that the image sideband amplitude remains low after a frequency multiplier. A SSBM provided by Miteq Company presents high enough rejection levels to be assembled with frequency multipliers. Based on this SSBM, we developed a simple microwave scheme suitable for all Tore-Supra reflectometers—from 50 to 155 GHz, dedicated either to density profile reconstruction or to density fluctuation measurements. Compared to the double sideband modulator previously used, SSBM offers higher signal to noise ratio and enables fixed frequency measurements, paving the way for new measurement techniques.