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Journal of Radio Electronics

Study of monolithic harmonic mixer based on HTSC josephson junction

Ekaterina A. Matrozova, L. S. Revin

Published Feb 1, 2025• 1 citation
Publisher

Abstract

A monolithic mixer based on a HTSC YBCO Josephson junction located entirely on a chip was investigated. Due to its compactness, such a mixer should have a higher signal transmission efficiency compared to mixers with spaced elements. In addition, the small size of the mixer can be critical for a number of applications. In the presented work, electromagnetic modeling of the monolithic mixer is carried out, its conversion efficiency is estimated based on the analytical approach proposed by the authors, and the obtained results are compared with experimental data. It is shown that the monolithic mixer has a sufficient conversion efficiency for a practical use and allows to mix a high-frequency 600 GHz signal with a low-frequency reference signal with a frequency of less than 10 GHz.

DOI
10.30898/1684-1719.2025.2.5

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A monolithic mixer based on a HTSC YBCO Josephson junction located entirely on a chip was investigated. Due to its compactness, such a mixer should have a higher signal transmission efficiency compared to mixers with spaced elements. In addition, the small size of the mixer can be critical for a number of applications. In the presented work, electromagnetic modeling of the monolithic mixer is carried out, its conversion efficiency is estimated based on the analytical approach proposed by the authors, and the obtained results are compared with experimental data. It is shown that the monolithic mixer has a sufficient conversion efficiency for a practical use and allows to mix a high-frequency 600 GHz signal with a low-frequency reference signal with a frequency of less than 10 GHz.
This paper presents an electromagnetic simulation of YBaCuO superconducting Josephson mixer for terahertz frequency band coupled with a log-periodic antenna. The proposed mixer design includes an on-chip diplexer and bias-tee. This approach reduces signal transmission losses, improves circuit isolation and makes the device very compact. The theoretical approach to the description of high-harmonic mixing proposed by the authors allows us to estimate the mixer conversion efficiency for experimentally obtained parameters of Josephson junctions. Comparison of experimental data with the theory showed the applicability of the suggested approach for a qualitative description of the mixer operation and allowed to estimate the efficiency of the simulated monolithic mixer.
Abstract This paper presents a monolithic high-temperature superconducting K-band sub-harmonic Josephson mixer using a pair of reverse-biased Josephson junctions (JJs), which are biased using reversed DC current. The sub-harmonic mixer can provide higher conversion gain and stronger rejection of the even-order harmonics of the local oscillator signal. A matching circuit with several bandpass filters (BPFs) is designed to match the junctions and achieve a maximum conversion gain. Based on the circuit configuration and using the established Verilog-A JJ mixer model, transient simulation has been done in the circuit simulator. An electromagnetic (EM) model is built and simulated in a full-wave simulation environment, and the results reveal that the design realizes very low loss at 25 GHz, excellent port isolation and high conversion efficiency. A prototype has been fabricated and tested in a cryocooler at operating temperatures of 40 K and 20 K. Measurements have experimentally verified the novel radio frequency design and simulation results. Maximum conversion gains of −10.5 dB and −6.5 dB were obtained at 40 K and 20 K, respectively, with a bandwidth greater than 400 MHz and outstanding gain linearity. It is also predicted that the mixer performance can be further improved with higher critical current I c values and identical or similar I c values between two parallel junctions.
This paper presents theoretical analysis and modeling of YBaCuO superconducting Josephson mixer for terahertz frequency band. The study was carried out both for the mixing at the first harmonic and for the case of high harmonic mixing. The numerical solution based on resistively shunted junction model was obtained for the YBaCuO junction with typical experimental parameters. Optimizing mixer performance included choosing the proper operating point and the local oscillator power. A study on the effect of RF input power, frequency and the harmonic number on conversion efficiency was carried out. The theoretical predictions presented in the work provide a simple method for optimal control of the Josephson mixer and demonstrate good qualitative agreement with direct modeling. For the first time, the optimum of the conversion efficiency versus signal frequency was analytically obtained.
Microwave superconducting mixers operating at 10–13 GHz utilizing Josephson junctions have been investigated analytically and experimentally. Measurements on mixer sensitivity were carried out at 13 GHz using waveguide-mounted experimental point-contact Josephson junctions at 4.2 K. Results showed sensitivities of −90 dBm/MHz (10−18 W/Hz) which included mismatch losses encountered in the waveguide structure. The Josephson junction mixing mechanism was analyzed on the basis of small-signal modulation of the staircase like dc I-V characteristics. It was shown that a small-signal microwave excitation results in an ac lateral shift of the regions between steps, such that: (a) Optimum Josephson mixing occurs halfway between steps. (b) Mixing occurs between all steps with maximum conversion efficiency between the zero and first step. (c) Predicted low conversion loss and possibly internal gain for a matched mixer. The analytical model was simulated by a digital computer and the behavior of the Josephson mixer predicted for various conditions of excitation. The model chosen for the analysis and the computer simulation is based on the simplest assumptions concerning bulk-formed Josephson junctions. In the laboratory an external local oscillator set 60 MHz below the signal frequency was used to induce the well-known step structure in the dc I-V characteristic of the point-contact Josephson junction. Mixing of the Lo and signal was found to occur between constant voltage steps in agreement with both analysis and computer simulation. The correctness of the model is demonstrated by the agreement between the theory and experiment.
© 2014 IOP Publishing Ltd. A high-Tc superconducting (HTS) monolithic microwave integrated circuit (MMIC) Josephson down-converter that approaches zero conversion loss is reported. The all-HTS YBa2Cu3O7-x thin-film circuit consists of a step-edge Josephson junction mixer, a 10-12 GHz bandpass filter for the RF input, a lowpass filter for the IF output and a resonant strip line for local oscillator isolation; all are integrated on a single 10 mm × 20 mm MgO substrate. The DC characteristics of the junction and its mixing properties have been experimentally studied and compared to the results of (a) a single Josephson mixer without the on-chip HTS filters, and (b) our previously reported MMIC down-converter which had very different junction characteristics. The Josephson junction parameters are analysed to give insight into their effect on the mixer performance.
The Commonwealth Scientific and Industrial Research Organization has developed superconducting microwave monolithic integrated circuit (MMIC) mixers using step-edge Josephson junctions and on-chip filters, made from YBaCuO on MgO substrates. Integration into an MMIC results in a compact and efficiently coupled structure. These have been shown to have outstanding conversion efficiency, dynamic range, and linearity. We report here a range of simulations of this type of mixer. We have mainly used Josephson simulators and analyze the data in both the time and frequency domains. More recently, we have also used microwave simulators incorporating a novel Verilog-A Josephson junction model that we have developed. We have looked at the interactions of junction bias current, local oscillator power, and radio-frequency input power with conversion efficiency, dynamic range, and linearity. Good agreement is found overall with measurements.