A Calibration Method for an Imbalanced Microwave Homodyne Readout for THz MKIDs

Microwave Kinetic Inductive Detectors (MKIDs) are emerging as a major detector choice for THz telescopes. Microwave IQ mixers are often used in the readout system of MKIDs. Their output signals (i.e., I and Q) have imbalance in common, which may limit their dynamic range and the measurement accuracy for MKIDs. In this paper we propose a calibration method by using two independent signal sources that are set at the same frequency but not synchronized (i.e., with small random fluctuation in frequency difference). The dynamic range of an IQ mixer and the noise spectral density of MKIDs are investigated with this calibration scheme.