Development of 2-D Antenna Array for Microwave Imaging Reflectometry in LHD

A 2-D antenna array for the Microwave Imaging Reflectometry (MIR) has been developed for the Large Helical Device (LHD). The MIR is a method of electron density diagnostics by the use of microwave radar techniques to obtain 2-D/3-D images of electron density fluctuations for the investigation of micro-turbulence and magneto-hydrodynamic instabilities in magnetically confined plasmas. The antenna array consists of five antennas in the toroidal direction and eight ones in the poloidal direction, respectively. As a test of an antenna element, a pyramidal horn antenna in the frequency range of 10-15 GHz was compared with the Yagi-Uda antenna. Based on the test results of the lower frequency antenna element, we manufactured a 2-D horn antenna array in the frequency rang of 50-75 GHz.