Recently we proposed so-called bi-SQUID based on a 3-junction SQUID circuit capable of providing highly linear voltage response. In this report, we present the experimental evaluation of series arrays of 20 and 128 bi-SQUIDs fabricated with a 4.5 kA/cm² Nb process as well as a prototype of an active electrically small antenna based on series array of 12 bi-SQUIDs. Both the origins of imperfections of the observed response linearity and the possible ways of the linearity improvement are discussed.

Differential circuits consisting of two series arrays of 10-junction parallel SQIFs were developed, designed and fabricated with 4.5 kA/cm² Nb HYPRES process. The differential voltage response evolution with applied magnetic field providing opposite frustration of the serial arrays was analysed in detail. Linear differential response with amplitude as high as 22 mV was observed for the serial arrays of 108 parallel SQIFs. It was shown that the response linearity is kept within some range of the applied frustrating magnetic field.

Superconducting Quantum Arrays (SQAs) based on integration of quantum cells each consisting of two Josephson-junction parallel arrays [Differential Quantum Cell (DQC)] are analyzed for applications in broadband radio frequency systems. These SQAs are capable of providing highly linear magnetic signal to voltage transfer with high dynamic range. Both detail study of the quantum cells with realistic parameters and analysis of their characteristics, including voltage response linearity, are presented and discussed. A prototype of an active electrically small antenna is implemented based on an SQA containing 560 DQCs. We demonstrated the SQA voltage response swing as high as ~ 100 mV at a transfer factor of ~ 6.5 mV/μT.

A new type of broadband active electrically small antenna (ESA) based on superconducting quantum arrays (SQAs) has been proposed and developed. These antennas are capable of providing both sensing and amplification of broadband electromagnetic signals with a very high spurious-free dynamic range (SFDR)—up to 100 dB (and even more)—with high sensitivity. The frequency band can range up to tens of gigahertz, depending on Josephson junction characteristic frequency, set by fabrication. In this paper we review theoretical and experimental studies of SQAs and SQA-based antenna prototypes of both transformer and transformer-less types. The ESA prototypes evaluated were fabricated using a standard Nb process with critical current density 4.5 kA cm ⁻² . Measured device characteristics, design issues and comparative analysis of various ESA types, as well as requirements for interfaces, are reviewed and discussed.

Using numerical simulation, we investigate the output power and loading tradeoffs for Superconducting Quantum Arrays (SQAs) suggested for the implementation of broadband radio-frequency systems, including active electrically small antennas capable of providing highly linear transfer characteristics with a high dynamic range. Standard matching loads used for linear microwave networks, including passive antennas, are not applicable for the active SQA-based circuits generally due to the strong shunting effect restricting the attainable linearity. At the same time, the output power of an active device can be increased by a power supply even for the impedance-mismatched circuits. Both the optimum achievable balance of the shunt effects and getting the required output power are analyzed and discussed in detail.