CHIME FRB: An application of FFT beamforming for a radio telescope
  We have developed FFT beamforming techniques for the CHIME radio telescope,
to search for and localize the astrophysical signals from Fast Radio Bursts
(FRBs) over a large instantaneous field-of-view (FOV) while maintaining the
full angular resolution of CHIME. We implement a hybrid beamforming pipeline in
a GPU correlator, synthesizing 256 FFT-formed beams in the North-South
direction by four formed beams along East-West via exact phasing, tiling a sky
area of ~250 square degrees. A zero-padding approximation is employed to
improve chromatic beam alignment across the wide bandwidth of 400 to 800 MHz.
We up-channelize the data in order to achieve fine spectral resolution of
$\Delta\nu$=24 kHz and time cadence of 0.983 ms, desirable for detecting
transient and dispersed signals such as those from FRBs.
