Prototype of 21-GHz band beam forming network for array-fed imaging reflector antenna

A 21-GHz band satellite broadcasting system is being studied as a means of delivering 8K (Super Hi-Vision), 3DTV and other advanced forms of broadcasting. We assumed the use of two 300-MHz wideband channels in the 21.4 to 22.0- GHz band and devised an array-fed imaging reflector antenna (array-fed IRA) to supply enough power for a transponder with such a wide band. The array-fed IRA effectively exploits limited resources because it can control radiation patterns; the 21-GHz band suffers from severe fading due to rain. To confirm the feasibility of the array-fed IRA system, we are currently manufacturing an engineering model of an array-fed IRA, which has a beam forming network (BFN) and a feed array consisting of 32 horn antennas, for a 21-GHz band broadcasting satellite. To evaluate the characteristics of the BFN, we fabricated and tested a prototype of the BFN composed of a 32-divider, 32 phase shifters, and 32 attenuators. Measured results showed that the BFN complies with our requirements.