Bends in Oversized Rectangular Waveguide

The use of rectangular oversized waveguides in the Main Transmission Lines of the Lower Hybrid Current Drive (LHCD) system of ITER, requires to investigate the problem of bends. The principal specifications that characterize the oversized bend design concern the minimization of the reflection of the fundamental mode and the maximization of its transmission, limiting at the same time its coupling to spurious modes that could propagate at the operational frequency. In this paper, the performances of bends with different geometries are compared. They are simulated using the commercial finite element software Ansoft HFSS. An innovative modified mitre-bend solution with trapezoidal-elements is proposed and analyzed.