New IQ demodulator development in diagnostic equipment for fusion energy research

New IQ demodulator, which will be used in the reflectometry system, was developed for the Alcator C-Mod experiments. Because the demodulator itself is a 4 mm × 4 mm integrated circuit chip and has very wide operational bandwidth (0.7 GHz – GHz), it can be mounted on a circuit board with its low frequency IQ outputs connecting directly to gain control and dc offset adjustment circuits. This whole circuitry is realized on a 4′×2.5″ printed circuit board and can be well tailored to meet the requirements for any type of data collection system. Since the RF and LO ports are operated at very narrow bandwidth in this application, single stub match circuits are designed to improve the ports matching as well as serve as a single pole filter.