SQIF Antenna Measurement in Near Field

We have been developing superconducting microwave (8-15 GHz bandwidth) magnetic field receiving antennas based on a two-dimensional (2D) Superconducting Quantum Interference Filter (SQIF) composed of bi-SQUID arrays. The 2D arrays are designed and fabricated using standard HYPRES niobium 4.5 kA/cm² process. The designed non-uniformity in inductances of bi-SQUID cells produces a pronounced zero-field antipeak in the flux-voltage response curve. We select the active antenna operation point by applying an appropriate dc flux bias current to set it in the middle of the antipeak linear slope. We measured comparative responses of the antenna with the SQIF dc bias at ON and OFF states when irradiated by a microwave signal from four different conventional planar ring and patch antennas placed in the near field.