A broadband 512-element full correlation imaging array at VHF (LEDA)

The Large Aperture Experiment to Detect the Dark Ages (LEDA) seeks to detect hyperfine line emission from neutral Hydrogen (λ
rest
∼ 21 cm; λ
obs
= 4–6 m) in the intergalactic medium ∼ 10
⁸
yr after the Big Bang. This is an era for which there are no data with which to directly constrain theory. LEDA is funded to deploy to station one of the Long Wavelength Array (i) a real-time, O(10–100) TFlops
⁻¹
, 512-input cross-correlator to enable full-sky full-Stokes imaging over 30–88 MHz, and (ii) dipole antennas for Dicke-switched total-power radiometry by which to detect the Hydrogen line. Project goals are discovery and development of new techniques and instrumentation. Key technical elements of LEDA include “large-N” cross correlation, nearly horizon to horizon broadband imaging, calibration of total-power radiometry using interferometric techniques, correction for direction-dependent receptor gains (e.g., due to mutual coupling), and correction for direction-dependent perturbation of incident wave fronts by the ionosphere.