Omniscopes: Large Area Telescope Arrays with only N log N Computational Cost

TL;DR

This paper introduces a new class of hierarchical antenna array layouts called omniscopes that enable large-scale, cost-effective radio telescope arrays with N log N computational complexity, facilitating advanced cosmological observations.

Contribution

It proposes hierarchical array configurations allowing efficient correlation computation via multi-dimensional FFTs, significantly reducing correlator costs for large radio telescope arrays.

Findings

Hierarchical arrays enable N log N correlation computation.

Such arrays support high sensitivity at multiple angular scales.

The approach facilitates large, cost-effective 21cm cosmology experiments.

Abstract

We show that the class of antenna layouts for telescope arrays allowing cheap analysis hardware (with correlator cost scaling as N log N rather than N^2 with the number of antennas N) is encouragingly large, including not only previously discussed rectangular grids but also arbitrary hierarchies of such grids, with arbitrary rotations and shears at each level. We show that all correlations for such a 2D array with an n-level hierarchy can be efficiently computed via a Fast Fourier Transform in not 2 but 2n dimensions. This can allow major correlator cost reductions for science applications requiring exquisite sensitivity at widely separated angular scales, for example 21cm tomography (where short baselines are needed to probe the cosmological signal and long baselines are needed for point source removal), helping enable future 21cm experiments with thousands or millions of cheap dipole-like antennas. Such hierarchical grids combine the angular resolution advantage of traditional array layouts with the cost advantage of a rectangular Fast Fourier Transform Telescope. We also describe an algorithm for how a subclass of hierarchical arrays can efficiently use rotation synthesis to produce global sky maps with minimal noise and a well-characterized synthesized beam.