Hybrid antenna imaging arrays for plasma imaging

Summary form only given, as follows. Slot bowtie antennas have been previously utilized as array elements in both microwave electron cyclotron emission imaging (ECEI) and microwave imaging reflectometer (MIR) diagnostics for imaging electron temperature (T/sub e/) profiles and fluctuations, and density (n/sub e/) fluctuations, respectively, in tokamak magnetic fusion plasmas. Recently, planar dual dipole antennas have been successfully developed to replace slot bowtie antennas. These antennas offer a number of advantages over the slot bowtie antennas, including increased sensitivity, reduced sidelobe levels, and reduced interchannel spacings which allow for higher resolution imaging. Antenna development activities have proceeded in four stages. First, detailed computer simulations were made using IE3D, a full wave method of moments electromagnetic simulation code. Here, the effects of antenna lead lengths, widths and spacing were studied with and without insitu RF filters. Successful designs were then fabricated on hybrid printed circuit boards employing millimeter-wave beamlead diodes. Here, subarrays consisting of four array elements in close proximity were characterized over a large RF bandwidth to determine antenna patterns and crosstalk levels between adjacent channels. In this paper, details regarding the simulations and laboratory characterization are presented. Full 16 channel arrays optimized for MIR at 88 GHz and ECEI at 120-130 GHz have been designed, fabricated and installed on the TEXTOR tokamak. Photographs of these arrays together with focal plane patterns measured both in the laboratory and on site on TEXTOR, will also be presented.