Superconducting Quantum Arrays Research Articles

Active Superconducting Electrically Small Antennas: Design Issues of Basic Cells

We discuss design issues and present Nb-based layout designs of two basic cells for broadband active electrically small antennas based on superconducting quantum arrays. The cells are the differential array circuit and bi-SQUID. The cell layouts realize parameter values answering results of the in-depth theoretical analysis performed earlier for attaining the high-linearity voltage response to magnetic signal. The layouts are to give reference approaches to the antenna circuit designs to be fabricated using niobium process.

From single SQUID to superconducting quantum arrays

Superconducting quantum arrays (SQAs) capable of providing highly linear voltage response to magnetic signal and high dynamic range have been suggested and developed. Base elements of the arrays, quantum cells, were devised and studied in detail. Using niobium process, SQAs with different number of the cells and prototypes of the SQA-based broadband active electrically small antennas were fabricated and tested.

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.

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.

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.

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 $\sim$ 100 mV at a transfer factor of $\sim\!\! 6.5 \hbox{mV}/\mu\hbox{T}$ .

Superconducting Quantum Arrays for Broadband RF Systems

Superconducting Quantum Arrays (SQAs), homogenous arrays of Superconducting Quantum Cells, are developed for implementation of broadband radio frequency (RF) systems capable of providing highly linear magnetic signal to voltage transfer with high dynamic range, including active electrically small antennas (ESAs). Among the proposed quantum cells which are bi-SQUID and Differential Quantum Cell (DQC), the latter delivered better performance for SQAs. A prototype of the transformer-less active ESA based on a 2D SQA with nonsuperconducting electric connection of the DQCs was fabricated using HYPRES niobium process with critical current density 4.5 kA/cm2. The measured voltage response is characterized by a peak-to-peak swing of ~100 mV and steepness of ~6500 μV/μT.

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.

Active Electrically Small Antenna Based on Superconducting Quantum Array

We introduce Superconductive Quantum Arrays (SQAs) and propose to use these structures as active Electrically Small Antennas (ESA). Several prototypes of the active ESA were fabricated using Nb process with critical current density 4.5 kA/cm2 and experimentally evaluated. The magnetic field to voltage transfer function linearity up to 70 dB was measured, and transfer factor dV/dB up to 6.5 mV/{\mu}T was observed for the ESA prototype containing 560 cells.