Extension of steering angle in a square corrugated waveguide antenna

A theoretical study of the square waveguide antenna with corrugated walls was carried out with reference to experimental results. When the length of the waveguide, to which the Gaussian beam is injected obliquely, is changed, a recursive Gaussian beam with high efficiency radiates from the waveguide exit in the asymmetric or symmetric direction with respect to a waveguide axis at almost the same interval. Because the optimum waveguide length for maximum efficiency decreases stepwise with increasing injection angle, adjustment of the waveguide length is not continuous but discrete. This method enables the injection angle, which is limited to 10degrees in a fixed waveguide length, to be increased by about two times. This is applicable to an antenna for an ITER-electron cyclotron heating/current drive and also to a launcher for a small machine with a narrow port where a steering mirror cannot be installed. (C) 2003 Elsevier B.V. All rights reserved.