Nikolay V. Kolotinskiy

Superconducting Quantum Arrays

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.

Output Power and Loading of Superconducting Quantum Array

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.

Microwave Dynamics of Superconducting Quantum Cell

We present an analysis of the microwave dynamics of the Superconducting Quantum Cell (SQC) in the microwave field performed by means of 3-D numerical simulations using a two-plate model. The simulations are necessary for the realization of active electrically small antennas (ESAs) based on Superconducting Quantum Arrays composed of SQCs. It was found that the incident wave mainly affects the SQC through its magnetic component in the same way as a low-frequency magnetic field does. We suggested possible improvements of the cell design by taking into account the current and field distributions in the plate intersection, as well as the size effects.

High Linearity Voltage Response Parallel-Array Cell

We studied in detail a cell consisting of two parallel SQUID arrays or two parallel superconducting interference filters (SQIFs) connected differentially with the goal of achieving highly linear voltage response to magnetic signal. In these different cell designs, we accounted for realistic values of coupling inductances in contrast to limiting case of vanishing inductances considered earlier. We found that a cell based on regular parallel SQUID arrays produces higher linearity as compared to the cell based on SQIFs. This high-linearity cell can be used for realizing Superconducting Quantum Arrays (SQA) capable of providing a broadband, highly-linear magnetic field-to-voltage transfer function and high dynamic range.

Design Issues of HTS bi-SQUID

We suggest a solution in principle for implementation of bi-superconducting quantum interference devices (bi-SQUIDs) on the basis of bicrystalline technology for high-temperature Josephson junctions. Optimization of the device design and parameters is discussed. Examples of the possible bi-SQUID layouts are considered.

Size Effects in Active Superconductor Antennas

Despite the fact that active an electrically small antenna based on Superconducting Quantum Array forms output voltage which is independent of the antenna size to wavelength ratio, a small size effect can appear and limit the antenna output linearity with the ratio increase. We analyze the size effect in the active antennas of both transformer and transformer-free types.

Critical Current Spread and Thermal Noise in Bi-SQUID Cells and Arrays

We report on the detailed analysis of thermal noise, critical current spread, and parasitic elements influences on the bi-SQUID voltage response and its linearity. These results together with the results of our previous studies serve as a useful guidance in designing high-performance bi-SQUIDs and bi-SQUID arrays implemented in low-temperature superconductor or high-temperature superconductor for many applications such as linear low-noise amplifiers and high-sensitivity antennas.

A Guide to Active Antennas Based on Superconducting Quantum Arrays

We describe how to use correctly an active electrically small antenna (ESA) based on superconducting quantum array (SQA) to ensure a highly linear voltage output of the antenna. An interface to the antenna ought to realize strongly mismatched loading of the active ESA. To provide the optimal conjugation of the antenna with the load device such as a low-impedance superconductor analog-to-digital converter, several measures are formulated, including the assignment of the proper SQA design configuration and the implementation of a broadband superconducting impedance transformer in the interface waveguide line. A directional diagram of the SQA-based ESA has been obtained through a three-dimensional full-wave numerical simulation.

Shapiro Steps Induced by Resonance Irradiation

We consider a Josephson junction coupled to a high-quality parallel resonance circuit under microwave irradiation on the resonance frequency. The phase locking of Josephson oscillations, manifesting itself through Shapiro steps, is studied using an analytical theory developed for the circuit. Substantial change in the amplitude of the oscillating component of the Josephson phase within the phase-locking range determines specificity of the step behavior. This analysis is compared with the results of a numerical simulation.

Dimensional Effects Affecting the Linearity of Active Superconducting Antennas

Active electrically small antennas (ESAs) based on superconducting quantum arrays (SQAs) exhibit similar sensitivity to the polarization direction as conventional magnetic ESAs. While active ESAs produce an output voltage independent of the size-to-wavelength ratio with respect to both the quantum cell and the SQA, distinct dimensional effects can appear and limit the linearity of the antenna output as this ratio increases. We analyze these dimensional effects in SQA-based active antennas of both transformer and transformer-free types.