Low cost RF over fiber distribution for radio astronomy phased arrays

Arguably RFoF has found wide application in broadband cable TV (CATV) systems and more recently in wireless cell applications. The use of RFoF also has a history in Radio Astronomy (RA) instrumentation. Typically in the distribution of high quality Local Oscillator reference signals to reflector antennas. On the scale of a small number of reflector antennas there are several examples where Directly Modulated (DM) laser diodes or Externally Modulated (EM) RFoF links have been used for wideband RF or IF transmission of the radio astronomy signal bandpass from the receiver package back to a centralized digital signal processing rack. In the last decade the radio astronomy community has developed an appetite for wide field of view, large N phased arrays, essentially N element distributed antenna systems (DAS). The Square kilometre Array (SKA), the Murchison Widefield Array (MWA) and the Australian Square Kilometre Array Pathfinder (ASKAP) all have thousands of receptors. ASKAP in particular is already demonstrating a 6840 RFoF link based DAS architecture with 36 remotely located 12m reflector antennas and RFoF spans up-to 6km. Each reflector having a 188 element L-Band phased planar array feed (PAF) at the prime focus. In this paper we report our development of the low cost RFoF “building block” for the generic RA signal transmission application.