Embedding Impedance Research Articles

Investigation of signal coupling circuit for NbN-based SIS mixer operated at 650 GHz

Superconductor-insulator-superconductor (SIS) mixers are the most sensitive coherent detectors in the terahertz region and are extensively utilized in astronomical research and atmospheric observation. In order to improve the detection accuracy of frequency, reduce the loss of signal in the transmission path, and reduce noise temperature, it is important to design a signal coupling circuit with high coupling efficiency. In this paper, with the help of a high-frequency structure simulator, a signal coupling circuit was designed based on a waveguide NbN-based SIS mixer at 650 GHz. The return loss and embedding impedance of this SIS mixer were investigated from 600 to 720 GHz. The effects of the SIS mixer chip’s bow-tie probe angle, substrate thickness, and chip slot height were calculated and analyzed. The results show that the return loss is lower than -16 dB in the 600 to 720 GHz band, and the embedding impedance is around 60 Ω, which can provide a good reference for the development of waveguide SIS mixers.

Preparation of lithium iron phosphate composites by electrodeposition with a tunnel structure on aluminium foil surface

In this paper, aluminium foil with a tunnel structure was used as a cathode to prepare a lithium iron phosphate composite by electrochemical deposition using propylene carbonate as the electrolyte solvent, and lithium nitrate, ferric nitrate and phosphoric acid as raw materials. The results show that the positive electrode composite is composed of a mixture of an olivine structured LiFePO4 and polyanion Li9Al3P8O29. The chemical composition of the mixture is related to the voltage of the electrochemical deposition and the acidity of the electrolyte solution. For a voltage of 1.8V and pH of 1.0, the composite material deposited in the tunnel of the aluminium foil takes the form of a one-dimensional nanotube, with a particle size ranging from 80nm to100nm. The composite material is closely combined with the aluminium foil. The aluminium foil can be directly used as a positive current collector, with a lithium sheet as the negative electrode. After mounting into a battery, an electrochemical performance test is performed. The battery test results show an initial discharge capacity of 95mAh/g, 79mAh/g and 59mAh/g at 0.1C, 0.2C and 0.5C, respectively. After the material is doped with magnesium and cobalt, the initial discharge capacity of the battery is 100mAh/g and 130mAh/g, respectively, at a rate of 0.1C. The cyclic voltammetry analysis of the battery show that after electrochemical deposition of the element, the symmetry between the oxidation and reduction peaks is increased, and the difference between the oxidation and reduction peak potentials is reduced. Element doping improves battery cycle performance. The AC impedance analysis show that the embedding impedance for lithium ions at the SEI interface is reduced from 300Ω to 250Ω, 100Ω after doping with magnesium, and cobalt. And the reaction mechanism of electrochemical deposition is discussed.

Lens‐coupled folded‐dipole antennas for terahertz detection and imaging

The authors report the design, simulation and characterisation of lens-coupled folded-dipole antennas (LC-FDAs) for terahertz (THz) detection and focal-plane imaging arrays. LC-FDAs operating at 200 GHz have been designed on semi-insulating silicon wafers with a resistivity larger than 20 000 Ω·cm. Even–odd mode analysis (EOA) has been performed to extract the currents of the two modes. The embedding impedance of the designed LC-FDAs has been simulated using conventional numerical electromagnetics, and the results show that a wide range of impedance values (both real and imaginary parts) can be achieved by changing the antenna geometry. This property makes LC-FDAs suitable for high-performance THz detectors in which impedance matching between antennas and devices is desired. From the currents calculated using EOA, the LC-FDA far-field radiation patterns, antenna directivity and Gaussian coupling efficiency for different lens structures have been examined using ray-tracing techniques. Good agreement between calculation results and measurement has been observed demonstrating the effectiveness of the above analysis approach. The single element FDA design has also been explored for use in high-resolution two-dimensional THz focal plane arrays by optimising the lens structure and evaluating the off-axis radiation patterns.

A Frequency Selective Surface Based Focal Plane Receiver for the OLIMPO Balloon-Borne Telescope

We describe here a focal plane array of Cold-Electron Bolometer (CEB) detectors integrated in a Frequency Selective Surface (FSS) for the 350 GHz detection band of the OLIMPO balloon-borne telescope. In our architecture, the two terminal CEB has been integrated in the periodic unit cell of the FSS structure and is impedance matched to the embedding impedance seen by it and provides a resonant interaction with the incident sub-mm radiation. The detector array has been designed to operate in background noise limited condition for incident powers of 20 pW to 80 pW, making it possible to use the same pixel in both photometric and spectrometric configurations. We present high frequency and dc simulations of our system, together with fabrication details. The frequency response of the FSS array, optical response measurements with hot/cold load in front of optical window and with variable temperature black body source inside cryostat are presented. A comparison of the optical response to the CEB model and estimations of Noise Equivalent power (NEP) is also presented.

Mixer-Based Characterization of Millimeter-Wave and Terahertz Single-Anode and Antiparallel Schottky Diodes

This paper presents an alternative characterization method to the traditional characterization methods of the millimeter-wave and terahertz Schottky diodes. The diodes can be characterized based on the mixer operation (conversion loss and noise temperature) under comparable conditions. The tuning of the embedding impedances and the easy changing of the diode under test allow the comparison of different diodes in their actual operating environment. A fundamental mixer test jig and a subharmonic mixer test jig are designed for the characterization and comparison of different single-anode and antiparallel Schottky diodes, respectively, at 183 GHz. For the antiparallel diodes, the traditional capacitance extraction is not possible, thus alternative and additional characterization data is valuable. The diode manufacturers can exploit the mixer-based characterization to test the mixer operation of their diode and to reveal possible problems with the diode during the diode development process.

W-band high output power Schottky diode doublers with quartz substrate

W-band quartz based high output power fix-tuned doublers are analyzed and designed with planar Schottky diodes. Full-wave analysis is carried out to find diode embedding impedances with a lumped port to model the nonlinear junction. Passive networks of the circuit, such as the low pass filter, the E-plane waveguide to strip transitions, input and output matching networks, and passive diode parts are analyzed by using electromagnetic simulators, and the different parts are then combined and optimized together. The exported S-parameters of the doubler circuit are used for multiply efficiency analysis. The highest measured output power is 29.5 mW at 80 GHz and higher than 15 mW in 76–94 GHz. The highest measured efficiency is 11.5% at 92.5 GHz, and the typical value is 6.0% in 70–100 GHz.

Design of a W-band Frequency Tripler for Broadband Operation Based on a Modified Equivalent Circuit Model of GaAs Schottky Varistor Diode

This paper presents the design and experimental results of a W-band frequency tripler with commercially available planar Schottky varistor diodes DBES105a fabricated by UMS, Inc. The frequency tripler features the characteristics of tunerless, passive, low conversion loss, broadband and compact. Considering actual circuit structure, especially the effect of ambient channel around the diode at millimeter wavelength, a modified equivalent circuit model for the Schottky diode is developed. The accuracy of the magnitude and phase of S21 of the proposed equivalent circuit model is improved by this modification. Input and output embedding circuits are designed and optimized according to the corresponding embedding impedances of the modified circuit model of the diode. The circuit of the frequency tripler is fabricated on RT/Rogers 5880 substrate with thickness of 0.127 mm. Measured conversion loss of the frequency tripler is 14.5 dB with variation of ±1 dB across the 75 ~ 103 GHz band and 15.5 ~ 19 dB over the frequency range of 103 ~ 110 GHz when driven with an input power of 18 dBm. A recorded maximum output power of 6.8 dBm is achieved at 94 GHz at room temperature. The minimum harmonics suppression is greater than 12dBc over 75 ~ 110 GHz band.

Millimeter-wave fixed-tuned subharmonic mixers with planar Schottky diodes

Two different frequency bandwidth subharmonic mixers (SHM) using planar Schottky mixing diodes are discussed and fabricated. Full-wave analysis is carried out to find the optimum diode embedding impedances with a lumped port for modeling the nonlinear junction. The SHM circuit is divided into several different parts and each part is optimized using the calculated diode impedances. The divided parts are then combined and optimized together. The exported S-parameter files of the global circuit are used for conversion loss (CL) discussion. For the 150 GHz SHM, the lowest measured CL is 10.7 dB at 153 GHz, and typical CL is 12.5 dB in the frequency range of 135–165 GHz. The lowest measured CL of the 180 GHz SHM is 5.8 dB at 240 GHz, and typical CL is 13.5 dB and 11.5 dB in the frequency range of 165–200 GHz and 210–240 GHz, respectively.

A Large-Signal Graphene FET Model

We propose a semi-empirical graphene field-effect-transistor (G-FET) model for analysis and design of G-FET-based circuits. The model describes the current-voltage characteristic for a G-FET over a wide range of operating conditions. The gate bias dependence of the output power spectrum is studied and compared with the simulated values. Good agreement between the simulated and the experimental power spectrums up to the third harmonic is demonstrated, which confirms the model validity. Moreover, S-parameter measurements essentially coincide with the results obtained from the simulation. The model contains a small set of fitting parameters, which can be straightforwardly extracted from S-parameters and dc measurements. The developed extraction method gives a more accurate estimation of the drain and source contact resistances compared with other approaches. As a design example, we use a harmonic balance load-pull approach to extract optimum embedding impedance values for a subharmonic G-FET mixer.

High-Performance 110-140-GHz Broadband Fixed-Tuned Varistor Mode Schottky Diode Tripler Incorporating CMRC for Submillimeter-Wave Applications

In this study, the design and fabrication of a 110-140-GHz varistor mode frequency tripler made with four Schottky diodes pair are presented. Nonlinear simulations were performed to calculate the optimum diode embedding impedance and the required input power. A compact microstrip resonant cell (CMRC) filter was introduced for the first time in submillimeter multiplier, instead of the traditional low-and-high impedance microstrip filter. The shorter size and the wider stop band of the CMRC filter improved the performance of the tripler. The tripler exhibited the best conversion efficiency of 5.2% at 129GHz and peak output power of 5.3mW at 125GHz. Furthermore, within the output bandwidth from 110 to 140GHz, the conversion efficiency was greater than 1.5%.

Integrated 585-GHz Hot-Electron Mixer Focal-Plane Arrays Based on Annular Slot Antennas for Imaging Applications

We have developed 585-GHz quasi-optical mixers and focal-plane arrays (FPAs) comprised of planar annular slot antennas (ASAs) with integrated niobium hot-electron bolometers for imaging applications. In order to optimize the single-element mixer design, the embedding impedance of the single ASA presented to the bolometer is analyzed using the induced electromotive force (EMF) method by including the antenna feed contribution. This approach has been further expanded to analyze the ASA self-impedance and mutual impedance in an array by utilizing the even-odd mode analysis. In addition, the far-field radiation patterns of the ASAs mounted to an extended hemispherical high-resistivity silicon lens have been calculated using the ray-tracing techniques. The details of circuit design and fabrication are presented in this study. Single mixer element measurement results have shown that a conversion gain of -11.9 dB and a double-sideband (DSB) receiver noise temperature of ~650 K have been achieved. Initial array imaging experiment results are presented and show excellent agreement with theory and simulation data. A spatial resolution of ~2.75 mm has been demonstrated at 585 GHz for a 1-D mixer FPA that is capable of diffraction-limited imaging. <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> -factor measurements show DSB mixer noise temperatures of 1675 and 3517 K with mixer conversion gains of -14.73 and -17.74 dB, respectively, have been obtained for two adjacent elements in a mixer array, which is comparable to the results reported in the literature.

An 85–115 GHz SIS Mixer Demonstrating Nearly Constant Dynamic Resistance

We report the design and experiment results of 85-115 GHz SIS mixers that demonstrate nearly constant dynamic resistance and uniform conversion gain. The dynamic resistance close to 50 Omega allows stable bias and direct connection of the SIS mixer and the cryogenic low noise amplifier without an IF isolator. The tuning circuit consists of a single junction tuned by an equivalent shunt inductance and an impedance transformer used for impedance matching. Since the impedance transformer and the shunt inductance have opposite frequency-dependent admittances, we were able to eliminate the frequency-dependent components of the tuning circuit and managed to achieve nearly constant embedding impedance in the frequency range. Measurement results showing dynamic resistances ranging from 30 Omega to 50 Omega and conversion gain changing less than 3 dB reasonably agree with the simulations.

A 250 GHz Subharmonic Mixer Design Using EBG Technology

The design, manufacture and characterization of a sub-harmonic mixer operating in the millimeter wavelength range is described. The mixer combines for the first time electromagnetic band gap (EBG) technology (which improves the radiation features of the dipole antenna used to couple radiation to the mixer), with conventional local oscillator (LO) waveguide circuitry. The mixer is designed to operate in an RF frequency band around 250 GHz when supplied with a LO frequency between 115 and 135 GHz. The fixed IF frequency spans 2.5-3.5 GHz. Performance predictions were made using a combination of the finite elements (FE) method to compute the embedding impedance of the diodes and the harmonic balance analysis (HBA) to predict the noise temperature. A prototype mixer has been fabricated and tested. Best mixer performance (double side band (DSB) mixer noise temperature and conversion loss of 3000 K and 11.5 dB, respectively) was measured with a LO power level of about 5 mW. Good agreement is observed with the predicted performance.

Simplified Analysis of Resistive Mixers

This letter gives a simple method for calculation by hand of the conversion efficiency of resistive mixers. The method assumes the same embedding impedances at all mixing frequencies and the mixing element is modeled as a time varying reflection coefficient. This gives simple expressions for the conversion efficiency. It, therefore, allows analytical parameter studies of the impact of the embedding impedance and parameters of the mixing element on the conversion efficiency. The theory is developed in two stages. First at optimum local oscillator power and second for arbitrary power. The theory agrees well with verifying measurements made on a field-effect transistor (FET)-based resistive mixer.

Microwave bifurcation of a Josephson junction: Embedding-circuit requirements

A Josephson tunnel junction which is rf driven near a dynamical bifurcation point can amplify quantum signals. However, the bifurcation point will exist robustly only if the electrodynamic environment of the junction meets certain criteria. We develop a general formalism for dealing with the nonlinear dynamics of a Josephson junction embedded in an arbitrary microwave circuit. We find sufficient conditions for the existence of the bifurcation regime: (a) the embedding impedance of the junction needs to present a resonance at a particular frequency ${\ensuremath{\omega}}_{R}$, with the quality factor $Q$ of the resonance and the participation ratio $p$ of the junction satisfying $Qp⪢1$, and (b) the drive frequency should be low frequency detuned away from ${\ensuremath{\omega}}_{R}$ by more than $\sqrt{3}{\ensuremath{\omega}}_{R}∕(2Q)$.

Theoretical Simulation of the Mixing Performance of Distributed Superconducting Tunnel Junction Arrays at 1.2 THz

In this paper we focus on the numerical simulation of the mixing behaviors of distributed superconducting junction arrays at 1.2 THz. A novel type of superconducting tunnel junctions, i.e., NbN/AlN/Nb, which have a relatively high gap voltage (4.3 mV) and can reach a critical current density as high as several tens of kA/cm 2 , are proposed for this characterization along with conventional Nb/AlOx/Nb junctions. The former is incorporated with a NbN/SiO 2 /Al tuning circuit, and the latter with a Nb/SiO 2 /Al and a NbTiN/SiO 2 /Al tuning circuits. The noise performance, local-oscillator power requirement, IF bandwidth, and optimum embedding impedance are thoroughly characterized for the two types of distributed superconducting junction arrays.

A 385-500 GHz Low Noise Superconductor-Insulator- Superconductor Mixer for ALMA Band 8

We report on the design and experimental results of a fix-tuned Superconductor-Insulator-Superconductor (SIS) mixer for Atacama Large Millimeter/submillimeter Array (ALMA) band 8 (385-500 GHz) receivers. Nb-based SIS junctions of a current density of 10 kA/cm(2) and one micrometer size (fabricated with a two-step lift-off process) are employed to accomplish the ALMA receiver specification, which requires wide frequency coverage as well as low noise temperature. A parallel-connected twin-junction (PCTJ) is designed to resonate at the band center to tune out the junction geometric capacitance. A waveguide-microstrip probe is optimized to have nearly frequency-independent impedance at the probe's feed point, thereby making it easy to match the low-impedance PCTJ over a wide frequency band. The RF embedding impedance is retrieved by fitting the measured pumped I-V curves to confirm good matching between PCTJ and signal source. We demonstrate here a minimum double-sideband receiver noise temperature of 3 times of quantum limits for an intermediate-frequency range of 4-8 GHz. The mixers were measured in band 8 cartridge with a sideband separation scheme. Single-sideband receiver noise below ALMA specification was achieved over the whole band.

An Investigation of the Performance of the Superconducting HEB Mixer as a Function of Its RF Embedding Impedance

We have conducted an investigation of the optimal embedding impedance for a waveguide superconducting hot-electron bolometric (HEB) mixer. Three mixer chip designs for 800 GHz, offering nominal embedding resistances of 70 /spl Omega/, 35 /spl Omega/, and 15 /spl Omega/, have been developed. We used both High Frequency Structure Simulator (HFSS) software and scale model impedance measurements in the design process. We subsequently fabricated HEB mixers to these designs using 3-4 nm thick NbN thin film. Receiver noise temperature measurements and Fourier Transform Spectrometer (FTS) scans were performed to determine the optimal combination of embedding impedance and normal-state resistance for a 50 Ohm IF load impedance. A receiver noise temperature of 440 K was measured at a local oscillator frequency 850 GHz for a mixer with normal state resistance of 62 /spl Omega/ incorporated into a circuit offering a nominal embedding impedance of 70 /spl Omega/. We conclude from our data that, for low noise operation, the normal state resistance of the HEB mixer element should be close to the embedding impedance of the mixer mount.

A 100-GHz HBV frequency quintupler using microstrip elements

A new quintupler concept using a heterostructure barrier varactor has been fabricated and measured. The multiplier consists of a quartz circuit mounted in a full height crossed waveguide block, and hence uses a mixture of waveguide components and microstrip elements. The embedding impedance for the fundamental frequency is provided by tuneable backshorts, whereas conventional microstrip circuit elements are used for impedance matching for the third and fifth harmonic. This topology is highly suitable for monolithic integration, and a peak conversion efficiency of 4.9% was measured at 102.5GHz with an input power of 13dBm.

Scaled model measurement of the embedding impedance of a 660-GHz waveguide SIS mixer with a 3-standard deembedding method

In this paper, the embedding impedance of a 660-GHz superconductor-insulator-superconductor (SIS) mixer is investigated using a 100-times scaled-model with a new 3-standard deembedding technique. The mixer embedding impedance is extracted from the reflection coefficients measured at the waveguide port of the mixer for three different terminations at the SIS junction's feed point. The three standards chosen are open-circuit, short-circuit and resistive load. Measured results are compared with those simulated by a high-frequency structure simulator (HFSS).