Low-noise superheterodyne receiver array for ECEI and MIR

Superheterodyne receiver array has been widely used in ECEI and MIR to extract the temperature and plasma density fluctuation, respectively. The system downconverts RF signals to a much lower IF for easy filtering and processing. The current system employs Schottky diode as the mixing element, which is mounted directly on the antenna. The LO and RF signals illuminate the antenna simultaneously to produce desired IF signals. One big drawback is that the system generates large amount of noise due to the lack of low-noise amplifier (LNA) before the mixer. It also requires complicated lens system in order to facilitate simultaneous RF and LO illumination. Additionally, it's difficult to shield the circuits from stray heating power and interfering signals. New receivers are developed for improving the signal quality as well as the ease of measurement. The new circuit consists of compact GaAs MMICs integrated on low-loss liquid crystal polymer substrate. Low noise and high gain GaAs LNAs, mixers and even complete receivers are available as off-the-shelf chips for V and W band applications. Employing MMICs in plasma diagnostics not only dramatically improves signal integrity, the on-board LO signal supply also eliminates the lenses for simultaneous RF and LO illumination. Additionally, the new receiver employs horn antennas, which produces directive radiation and strong interference attenuation.