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IEEE Transactions on Microwave Theory and Techniques

Wideband Power-Dependent Power Limiter Based on Distributed Low-Temperature Superconductor rf-SQUIDs for Cryogenic RF Receivers

Navjot K. Khaira, Tejinder Singh, Raafat R. Mansour

Published Dec 1, 2022• 10 citations
Publisher

Abstract

A novel design of a radio-frequency (RF) power limiter for protecting sensitive superconductor receiver components from high-power microwave signals is presented. In this approach, two low-${T} _{c}$superconductor 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. The key concept is built on the fact that 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. This phenomenon is exploited to achieve the desired RF power-limiting operation. The device is fabricated using an eight-layer niobium-based superconducting process node SFQ5ee by MIT Lincoln Laboratory (MIT-LL). A monolithically integrated wideband hybrid coupler is used in this design as it dictates the bandwidth of the overall device. The operating frequency of the power limiter is 10 GHz with a 2-GHz bandwidth. The performance of the device is measured for input RF power levels ranging from −30 to +10 dBm, as well as arising intermodulation products are experimentally investigated. The output power increases linearly with the input power up to −15 dBm, and for higher power levels, the device offers an increasing attenuation to limit the output RF power starting above −15 dBm.

DOI
10.1109/tmtt.2022.3223873

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A novel design of a radio-frequency (RF) power limiter for protecting sensitive superconductor receiver components from high-power microwave signals is presented. In this approach, two low-Tc{T} _{c}Tc​superconductor 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. The key concept is built on the fact that 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. This phenomenon is exploited to achieve the desired RF power-limiting operation. The device is fabricated using an eight-layer niobium-based superconducting process node SFQ5ee by MIT Lincoln Laboratory (MIT-LL). A monolithically integrated wideband hybrid coupler is used in this design as it dictates the bandwidth of the overall device. The operating frequency of the power limiter is 10 GHz with a 2-GHz bandwidth. The performance of the device is measured for input RF power levels ranging from −30 to +10 dBm, as well as arising intermodulation products are experimentally investigated. The output power increases linearly with the input power up to −15 dBm, and for higher power levels, the device offers an increasing attenuation to limit the output RF power starting above −15 dBm.
We present the design, fabrication and testing of a low-temperature superconducting (LTS) analog microwave variable attenuator. The two-port circuit includes two 90ohybrid couplers and a phase shifter to realize a variable attenuation at the output port. The wideband analog phase shifter is implemented using LTS microstrip transmission line (TL) coupled to an array of radio frequency superconducting quantum interference devices (rf-SQUIDs). The phase shift is achieved by passing a dc current through a TL adjacent to the SQUID-loaded microstrip line which controls the flux through the rf-SQUIDs. The proposed variable attenuator shows more than 30 dB of precise analog flat attenuation tuning range over 8 GHz to 12 GHz with a dc control current ranging from 0 mA to 4.5 mA. The device exhibits a wideband operation with variable attenuation seen not only in theX-band but also inKu-band. The device is fabricated using a multilayer niobium-based superconducting process SFQ5ee by MIT Lincoln Laboratory, and has a compact footprint of 1.3 mm2. To the best of our knowledge, this is the first implementation of a variable attenuator using distributed rf-SQUIDs. This device has implications in a variety of applications such as cryogenic receivers and qubit circuit measurements.
This article presents a low-temperature superconductor (LTS)-based microwave phase shifter. The device utilizes a superconducting hybrid coupler monolithically integrated with two tunable reflective loads. An array of radio frequency superconducting quantum interference devices (rf-SQUIDs) is used to achieve inductive tuning in reflective loads, resulting in a broadband true time delay phase shift. The rf-SQUIDs are current controlled using an on-chip dc bias circuitry. The proof-of-concept fabricated device provides excellent RF performance in theX{X}X- and Ku -band with a phase shift of 49° at 10 GHz and 67° at 15 GHz. The insertion loss is < 1.5 dB for the entire range from 8 to 18 GHz. The methods to further improve the obtained phase shift are discussed. The overall device has a chip footprint of 0.6 mm2 and is fabricated using MIT-Lincoln Lab (MIT-LL) SFQ5ee eight-layer Niobium (Nb)-based superconducting fabrication process.
This letter presents a low-temperature superconductor (LTS)-basedX{X}X- andK{K}K-band analog ultra-wideband phase shifters realized by coupling an array of radio-frequency superconducting quantum interference devices (rf-SQUIDs) to a microwave transmission line (TL). The proposed device is realized using MIT-LL SFQ5ee eight-layer niobium-based process. The device is designed by distributing 2256 rf-SQUIDs coupled throughout the line exhibiting experimental analog current-controlled phase shift of 130° and insertion loss variation of 0.46 ± 0.23 dB inX{X}X-band atfc{f} _{c}fc​= 10 GHz. In theK{K}K-band, a phase shift of 328° and insertion loss of 2.5 ± 1 dB inK{K}K-band atfc{f} _{c}fc​= 22.5 GHz is observed. Theoretical analysis of the phase shifter is discussed.
Superconductor-based microwave and millimeter-wave components play a crucial role in various applications, particularly in superconductor-based digital receivers and superconductor-based quantum computing systems. This article aims to provide an overview of recent advancements in superconductor microwave and millimeter-wave devices implemented in a multilayer nio­bium fabrication process. These devices cover a broad frequency range, from 300 MHz to 100 GHz, and include bandpass/band-reject filters, wideband cou­plers, niobium-based microelectromechanical sys­tems switches, phase shifters, filters-based power protection circuits, phase shifter-based power limiters, tunable attenuators, and supercon­ductor-based magnet-less circulators.
A dc superconducting quantum interference device (SQUID) was used to amplify radio-frequency signals that were coupled to one end of the microstrip formed by the input coil and the SQUID washer. For one device, the resonant frequency of the microstrip was increased from about 200 to 620 MHz by progressively shortening the length of the coil. At an operating temperature of 4.2 K, the gain was typically 18 dB, and the system noise temperature ranged from 0.5±0.3 K at 80 MHz to 3.0±0.7 K at 500 MHz.
DC Superconducting Quantum Interference Devices (SQUIDs) are widely used to amplify low-level, radio frequency (rf) electrical signals. SQUID amplifiers offer low noise, high gain, and low power dissipation. One method of implementing a SQUID rf amplifier for frequencies from a few hundred megahertz to several gigahertz is to operate the integrated input coil on top of the SQUID washer as a microstrip resonator. This is achieved by applying the input signal between one end of the coil and the SQUID washer, which acts as a groundplane; the other end of the coil is left open. Substantial levels of gain can be achieved from the microstrip SQUID amplifier for a signal frequency at the fundamental resonant frequency of the microstrip, at which the length of the microstrip is equal to one-half wavelength, λ/2. Since the length of the microstrip has to be made shorter for higher frequencies, however, the mutual inductance between a SQUID with a given geometry and the microstrip—and thus the gain—decreases with increasing frequency. We show that a significantly enhanced gain can be achieved by operating the microstrip resonator in higher-order modes, for example, with a microstrip length of 3λ/2 or 5λ/2, provided the winding sense of the microstrip for each consecutive λ/2 section is reversed. For a 4λ/2 resonator, we demonstrate a gain of 24 dB at 2.6 GHz, an increase in gain of about 10 dB compared to a λ/2 resonator on a SQUID of the same geometry and characteristics.