Cross-Polarization Reduction in Kinetic Inductance Detectors Based on Quasi-Lumped Resonators

Kinetic Inductance Detectors (KIDs) have emerged as a leading technology for millimeter- and submillimeter-wave astronomy due to their high sensitivity, natural multiplexing capabilities and scalable fabrication. In polarization-sensitive applications-such as Cosmic Microwave Background (CMB) studies-cross-polarization, or unintended response to the orthogonal polarization, poses a significant limitation to measurement fidelity. This work investigates the origin of cross-polarization in meandered Lumped Element KIDs (LEKIDs), with particular emphasis on the role of parasitic currents in the interdigitated capacitor. A comparative study between conventional LEKIDs and a quasi-lumped resonator design is presented, demonstrating that removing the capacitive element may improve cross-polarization discrimination, confirming the capacitor's contribution to polarization leakage.