THREE-CHANNEL PHASE METERS BASED ON THE AD8302 AND FIELD PROGRAMMABLE GATE ARRAYS FOR HETERODYNE MILLIMETER WAVE INTERFEROMETER

The paper presents the results of research and development of two types of phase meters for heterodyne two-wave “unambiguous” interferometer designed to measure the plasma density in tokamak COMPASS. The aim of this work is the creation of a phase meter capable of measuring fast phase changes of each probing wave, and their phase difference. Plasma is probed by two microwave signals with different wavelengths propagating along identical paths to meet each other. Each analyzed signal acquires a certain phase shift j1 and j2, and the “unambiguous” interferometer determines the difference (j1 – j2). The phase measure-ent is carried out by using three-channel phase meters: a phase meter based on the pairs of the AD8302 and a phase meter based on field programmable gate arrays (FPGA). The proposed circuit decisions and algorithms of signal processing allow to measure phases in the range 0…360° in real time.