GroundBIRD Telescope: Systematics Modelization of MKID Arrays Response

Abstract

Kinetic inductance detectors are widely used in millimeter- and submillimeter-wave astronomy, benefiting from their fast response and relative ease of fabrication. The GroundBIRD telescope employs microwave kinetic inductance detectors at 145 and 220 GHz to observe the cosmic microwave background. As a ground-based telescope, it is subject to inherent environmental systematics, namely atmospheric emission and thermal fluctuations of the focal plane temperature. This study models resonance frequency shifts induced by each source using calibrated on-site measurements of precipitable water vapor and temperature. Comparison with observational data confirms the validity of the models and identifies atmospheric loading as the dominant contributor to frequency variation under typical observation conditions.

Figures (8)

• Figure 1: Schematic of a $145$ GHz MKID array installed in the GroundBIRD focal plane. The left panel depicts an individual MKID, with the active resonator section composed of NbTiN and Al, and the coupling region made solely of NbTiN. The right panel shows the full layout of an array containing $23$ MKIDs with lenses and antennas. The dark MKIDs are highlight by red circles.
• Figure 2: Frequency sweep measurement (blue) and its fit result to the transition model (red) of MKID $1$ on $\textrm{Array1B}$. Fitted parameters include resonance frequency, quality factors, cable delay, and phase offset.
• Figure 3: Standardized phase response TOD plots, measured under different conditions. In (a), one hour TOD from $\textrm{MKID\:1}$ on $\textrm{Array2B}$ (blue, left axis) measured at 9 RPM and evolution of the precipitable water vapor (red, right axis) are shown. The TOD shown in (b) was measured by $\textrm{MKID\:0}$ on $\textrm{Array2A}$ while intentionally varying the focal plane temperature conditions. The red curve indicates the focal plane temperature measured during a 20 RPM scan, prior to reaching thermal stabilization.
• Figure 4: Plot of the Izaña atmospheric observatory
• Figure 5: Fractional resonance frequency shift $\frac{\delta f_r}{f_{r0}}$ of MKID 0 on Array1B plotted against calibrated on-site PWV. The reference resonance frequency $f_{r0}$ is taken as the model-estimated value at $0\:\mathrm{mm}$ PWV. Colored points indicate different observation periods. The plot in (a) shows the primary dataset with the best-fit model (green dotted line) and $\pm2\sigma$ confidence interval (blue shaded region). The plot in (b) displays the same fit and confidence interval overlaid on an independent dataset for validation.