Broadband amplitude tapering for a linear W-band array antenna for Gaussian beam-shaping

A W-band horn array antenna is currently being developed for the Doppler reflectometry system on ASDEX Upgrade tokamak in Garching. The antenna is dedicated to radiate a well defined Gaussian beam over nearly the whole W-band (75GHz to 105GHz). As in-vessel moving parts have to be avoided, the underlying structure of the feed network is a series feed. This contribution examines a broadband coupling structure to couple a defined amount of power from the main feed line to the radiating elements. Its applicability is validated by measurements of a prototype coupling network and full-wave simulation of a 32-element series fed array antenna.