Measurement of Embedded Element Efficiencies of Wideband Dense Arrays in Reverberation Chamber

The paper describes how coupling efficiencies in dense arrays can be measured in a reverberation chamber. This is much faster than measuring S-parameters between all element ports and calculating the coupling efficiencies from these. Results are presented between 2 and 6 GHz for an array of 144 Vivaldi elements developed by ASTRON for use as a technology demonstrator for SKA (Square Kilometer Array). The results include coupling efficiencies for singly-excited elements (referred to as embedded element efficiencies), as well as for three different focal-plane-array excitations. The embedded element efficiencies are compared with an approximate formula derived from classical papers. The results show significant efficiency losses at low frequencies.