Simulation and Data Processing of Beamforming Experiments with Four 21CMA Stations

TL;DR

This paper develops a comprehensive simulation and data-processing framework for digital beamforming experiments with the 21CMA, validating calibration and imaging strategies for future upgraded array configurations.

Contribution

It introduces an end-to-end simulation and processing pipeline for 21CMA beamforming experiments, including realistic sky modeling and analysis of channelization effects.

Findings

Demonstrates the feasibility of current calibration and imaging strategies in digital beamforming mode.

Quantifies spectral modulation effects caused by two-stage channelization.

Provides a validated framework for future 21CMA beamforming observations.

Abstract

We present an end-to-end simulation and data-processing framework for digital beamforming experiments conducted with four stations of the 21 Centimeter Array (21CMA). Motivated by the need to characterize instrumental systematics, such as those arising from station-level digital beam synthesis and two-stage channelization, and to validate the data-processing pipeline framework for a future upgraded 21CMA with beamforming capability across all stations, we simulate interferometric visibilities using realistic four-station layouts with radio interferometer simulation software OSKAR. Two representative pointings are considered: a bright, complex Cassiopeia A field and a near-north celestial pole (NCP) calibration field. The sky model combines cataloged point sources with a diffuse Galactic component from the Global Sky Model (GSM), and frequency-dependent thermal noise is injected. We further quantify the imprint of two-stage channelization by comparing an ideal beamformer with a coarse-channel phase approximation, demonstrating that off-axis sources exhibit a characteristic piecewise-linear spectral modulation across coarse-channel boundaries. A data-processing pipeline, including Radio Frequency Interference (RFI) mitigation, calibration, imaging, and mosaicking steps consistent with current low-frequency radio astronomy practice, is constructed. The resulting synthetic images and background root-mean-square (RMS) noise measurements demonstrate the feasibility of adapting established 21CMA calibration and imaging strategies to digital beamforming modes, and provide a framework that can be further developed for beam-aware processing in future full-scale 21CMA beamforming observations.