Spectral-line performance of low-frequency radio telescope arrays: SKA-Low stations

Abstract

The effects of diffraction, reflection and mutual coupling on the spectral smoothness of radio telescopes becomes increasingly important at low frequencies, where the observing wavelength may be significant compared with the antenna or array dimensions. These effects are important for both traditional parabolic antennas, which are prone to the 'standing wave' phenomenon caused by interference between direct and scattered wavefronts, and aperture arrays, such as the SKA-Low, MWA, HERA, and LOFAR which have more complicated scattering geometries and added dependence on pointing direction (scan angle). Electromagnetic modelling of these effects is computationally intensive and often only possible at coarse frequency resolution. Therefore, using the example of SKA-Low station configurations, we investigate the feasibility of parameterising scattering matrices, and separating antenna and array contributions to telescope chromaticity. This allows deeper insights into the effect on spectral smoothness and frequency-dependent beam patterns of differing antenna configurations. Even for the complicated SKA-Low element design, band-limited delay-space techniques appear to produce similar results to brute-force electromagnetic models, and allow for faster computation of station beam hypercubes (position, frequency and polarisation-dependent point spread functions) at arbitrary spectral resolution. As such techniques could facilitate improvements in the design of low-frequency spectral-line surveys, we conduct a simulated Cosmic Dawn experiment using different observing techniques and station configurations.

18 pages, 14 figures, 5 tables; accepted for publication in PASA

References in corpus (10)

• Late-time cosmology with 21cm intensity mapping experiments
• The Epoch of Reionization Window: I. Mathematical Formalism
• A radio transient with unusually slow periodic emission
• Interplanetary Scintillation studies with the Murchison Wide-field Array II: Properties of sub-arcsecond compact sources at low radio frequencies
• Spectral Flattening at Low Frequencies in Crab Giant Pulses
• 21cmEMU: an emulator of 21cmFAST summary observables
• Imaging-spectroscopy of a band-split type II solar radio burst with the Murchison Widefield Array
• The Electromagnetic Characteristics of the Tianlai Cylindrical Pathfinder Array
• Sky-averaged 21-cm signal extraction using multiple antennas with an SVD framework: the REACH case
• Wide-Band Spectral Variability of Peaked Spectrum Sources