A millimeter wave beam shaping phased antenna array

A millimeter wave phased antenna array (PAA) serving as an electrically controlled "lens" is being developed for use in plasma imaging reflectometric diagnostics. To account for the rapid changes of the cutoff layer with plasma density variation, a true time delay (TTD) controlled phased antenna array (PAA) is being developed as an artificial lens with controllable focal length for launching the illumination beam of the microwave imaging reflectometry (NUR) system. Varactor diode loaded transmission lines, also called Nonlinear Delay Lines (NDL), are utilized in this electronic lens to control the time delays between each array element, and subsequently the wavefront of the probe beam. Proof of principle 1-D and 2-D PAAs have previously been demonstrated in beam steering systems. A 45 GHz monolithic NDL-based PAA is currently under development and will be installed on the National Spherical Torus Experiment (NSTX) in the near future.