V.K. Kornev, I.I. Soloviev, A.V. Sharafiev, N.V. Klenov
A new element, bi-SQUID realizing two successive nonlinear signal transformations answering the ones in rf and dc SQUIDs, is proposed. Setting the transformations mutually inverse, one can come to a highly linear magnetic field to voltage transfer function of the bi-SQUID. Analytical theory is developed and discussed. Results of experimental evaluation of serial arrays of bi-SQUIDs formed by niobium process with critical current density 4.5 kA/cm2 for Josephson tunnel junctions, are presented and analyzed. Impact of the critical current spread and the means for decrease of the impact on linearity of the array voltage response are considered. Special gradiometric topology of the bi-SQUID is suggested to be realized with submicron Josephson-junction process leaving superconducting screen out. The bi-SQUID with high linearity voltage response can be used as basic cell of superconducting quantum arrays allowing designing of both the high sensitive broad band amplifiers and the active electrically small antennas for sub-gigahertz and gigahertz frequency ranges. Such active antennas can be realized through integration of the arrays with either common or individual superconducting transformers as well as by use two-dimensional arrays with normal-metal cell-to-cell connection.