A single-FPGA real-time dual beam-former with FX correlation capabilities. First results at the Nançay radio telescope with the FAN antenna array

A full-time beam-former for two independent antenna groups, with visibility computation capabilities at a slower rate, have been formerly designed on a single FPGA for the BAO-radio instrument, a radio telescope demonstrator for the study of dark energy by HI probing technique. On the same FPGA, a firmware dedicated for the FAN project at the Nancay radio telescope have been designed, and can provide a full-time dual beam-forming on a single antenna group. It can process an incoming data flow of twelve channels organized each as complex spectrum (2×8bits) of 4096 frequency with a 4GbPS effective rate. The dual-beam capability of the system has been successfully tested on the FAN array with transits on CasA and 3C123 radio sources after a configuration by complex coefficients computed from previous off-line software correlations on CasA. Recently, another beam-forming on 3C123 has been done after a calibration on CasA performed by the beam-former set in correlation mode and a source-tracking.