A radio astronomy L-band phased array feed system using RF over fiber distribution

This is an overview of the system level RF design for the second generation architecture used in the Australian Square Kilometre Array Pathfinder (ASKAP) [1] design enhancement (ADE). ADE is a distributed antenna system (DAS) of 36 reflector antennas each 12m in diameter. Each antenna has a planar Phased Array Feed (PAF) at the prime focus. The PAF contains 188 broadband 700–1800MHz receptors. Inside a PAF the radioastronomy (RA) signals are amplified, band selected and converted to 188 individual broadband RF over (singlemode optical) fiber (RFoF) lightwaves [2]. The entire ADE array has 6840 RFoF links, this includes transmission line delay metrology for each reflector. The longest RFoF span is 6km. Optical to RF demodulation of the RF sky signal at the central site Digital Signal Processing (DSP) shielded building is direct sampled in 12bit analog to digital convertors (ADCs). Digital beamforming provides 36 pencil beams, each of 384MHz bandwidth. The scale of ADE represents a leap forward in applied RF and photonic techniques to enable a simpler, lower cost, more modular, EMC compliant, phased array receiver architecture. ADE will provide unprecedented high speed sky surveys with an instantaneous widefield of view (30deg 2 at 1420MHz) capability for a new generation of radio astronomers.