Cryogenic RF Power Limiter Using rf-SQUID Phase Shifting
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Solution Overview
Problem
Existing cryogenic RF receivers are vulnerable to damage from RF signals with low power levels above −15 dBm due to the high threshold power limitations of conventional power limiters, and existing superconducting power limiters suffer from excessive heating and limited monolithic integration capabilities.
Innovation Solution
A monolithic RF power limiter is developed using two low-Tc superconductor microstrip lines coupled with an array of rf-SQUIDs and hybrid couplers, which exploits the power-dependent phase shifting behavior to achieve effective power limiting at very low RF power levels, allowing for monolithic integration with other superconducting components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional power limiters are used, then they can provide power limiting function, but the threshold power level is high and cannot be reduced below a certain power level
Solution Approach 1:
The patent changes the operating parameters of the superconducting transmission line by controlling the magnetic flux through the SQUID loop, which modifies the critical current and thus the threshold power level. By adjusting the DC bias current through the SQUID, the system can dynamically set the power limiting threshold to very low levels (below -15 dBm), enabling protection of sensitive superconducting components that conventional limiters cannot protect.
2Power
If high temperature superconductor transmission line switching is used, then power limiting can be achieved, but excessive heating of the superconductor occurs and recovery is delayed
Solution Approach 1:
The patent introduces a low-Tc superconducting SQUID loop as an intermediary element coupled to the high-Tc superconducting transmission line. The SQUID acts as a flux-controlled switch that can modulate the effective impedance of the transmission line without requiring the high-Tc material itself to switch states. This intermediary mechanism enables power limiting while keeping the high-Tc line in its low-loss superconducting state, avoiding excessive heating and delayed recovery.
3Power
If semiconductor diode-based limiters are used, then power limiting can be provided, but the threshold power level is high and monolithic integration with superconducting components is not possible
Solution Approach 1:
The patent employs a composite structure combining low-Tc superconducting SQUID loops with high-Tc superconducting transmission lines. The low-Tc SQUID layer (e.g., Nb-based) is fabricated using standard superconducting thin-film processes and can be monolithically integrated with the high-Tc line (e.g., YBCO-based). This composite approach enables both low threshold power levels and seamless integration with superconducting receivers and quantum devices on the same substrate.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a threshold limiting power of −15 dBm with linear output power increase up to −15 dBm and increasing attenuation for higher power levels, demonstrating reliable protection for sensitive superconductor components and enabling integration with quantum measurement systems.
Implementation Method 1
two low-Tc superconductor (LTS) microstrip lines, one of which is coupled with an array of RF superconducting quantum interference devices (rf-SQUIDs)
Data Source
AI summary
A monolithic radio frequency (RF) power limiter for protecting sensitive superconductor receiver components from high-power microwave signals is disclosed. In some embodiments, two low-Tc superconductor (LTS) microstrip lines; one of which is coupled with an array of RF superconducting quantum interference devices (rf-SQUIDs); are combined with a pair of hybrid couplers to provide the power limiting operation at very low RF power levels. A microstrip line coupled to an array of rf-SQUIDs behaves as a power dependent phase shifter and its phase can be controlled by the input RF power. In one embodiment, a monolithically integrated wideband hybrid coupler is used as it dictates the bandwidth of the overall device.