System for tunerless operation of a four-element phased array antenna for fast wave current drive

A simple transmission line configuration for powering a four-element phased antenna array is described. This system, called the balanced feed configuration (BFC) is suitable for co- or counter-fast wave current drive (FWCD) applications. It has the property of presenting a constant matched load to the transmitter despite wide variations in the antenna load impedance without the use of variable tuning elements. This system has been implemented on a 2 MW 60 MHz FWCD antenna on the DIII-D tokamak.