Shielding requirements for ADE receivers

A single focal plane array receptor element in the ASKAP design enhancement (ADE) receiver system typically has a 40K LNA input noise temperature. For nominal conditions this is amplified by 70dB before RF over single mode fibre transmission to the central building for digitization and digital beam-forming. Shielding requirements for the ADE receivers are determined by three factors, these being unconditional gain stability over the 700MHz to 1800MHz band, very low cross talk between PAF elements and EMC susceptibility issues in the unlikely event a strong transient transmission presents. The crosstalk specification can be related to the phased array co-variance matrix (ACM). Measuring the shielding attenuation performance of very small electronics enclosures and subassemblies is particularly challenging. We use a number of test configurations including RF over fibre to electrically short radiators to replicate in-module emissions and enable realistic estimates of module shielding. This paper will briefly discuss the derivation of the specifications and the empirical techniques used to validate the prototype ADE receiver design.