Design and characterization of W-band and D-band calibration sources for the AliCPT-1 experiment

TL;DR

This paper presents the design and performance of W-band and D-band calibration sources developed for the AliCPT-1 telescope to ensure precise calibration of its optical performance in cosmic microwave background polarization measurements.

Contribution

The paper introduces novel calibration sources specifically designed for the AliCPT-1 experiment, enabling accurate characterization of its optical and polarization performance.

Findings

Successful development of W-band and D-band calibration sources

Calibration sources meet the performance requirements for AliCPT-1

Enhanced accuracy in polarization and beam measurements

Abstract

Ali Cosmic Microwave Background Polarization Telescope (AliCPT-1) is the first Chinese cosmic microwave background experiment aiming to make sensitive polarization maps of the potential B-mode signal from inflationary gravitational waves. The telescope was deployed on the Tibet Ali site at 5250 m above sea level in early 2025. Before and after each observation season, the instrument performance must be carefully calibrated, including the far field beam performance, far sidelobe, spectral response, polarization angle, and cross-polar beam response. To characterize these optical performances, several calibrators have been developed. We developed a W-band source and a D-band source for the AliCPT-1 telescope's beam characterizations. We present the design and performance of the two calibration sources.