S. Mohammad Hassan Javadzadeh | Shahed University (original) (raw)

Papers by S. Mohammad Hassan Javadzadeh

Research paper thumbnail of Non-linearity in superconducting coplanar waveguide rectangular-spiral resonators

IET Microwaves, Antennas & Propagation, 2015

ABSTRACT In the present work, a non-linear distributed circuit model for superconducting rectangu... more ABSTRACT In the present work, a non-linear distributed circuit model for superconducting rectangular-spiral resonators is proposed. This is based on an accurate non-linear circuit model for superconducting parallel coupled lines, which is simultaneously considered both quadratic and modulus non-linear dependencies. The non-linearity in superconducting devices depends on the current distribution, which is mainly determined by the geometrical structure of the device. The current distribution in the superconducting spiral resonators can be computed by a numerical approach based on three-dimensional finite element method. This computed current distribution is used to produce a non-linear circuit model for the superconducting spiral resonator. Numerical technique based on harmonic balance approach is used for non-linear analysis of the proposed equivalent non-linear circuit. The model is proposed for coplanar waveguide (CPW) resonators, which can easily be extended for microstrip resonators. To confirm the accuracy of the proposed model, non-linearity in a 6-pole superconducting CPW spiral bandpass filter has been measured. Measurement results show good agreement with the ones from the model. This proposed technique is found to be a major approach for fast and efficient non-linear analysis of the superconducting spiral resonators and filters.

Research paper thumbnail of Closed Form Formulas for Distributed Circuit Model of Discontinuities in HTS Microstrip Transmission Lines

Physics Procedia, 2012

A distributed circuit model for different kinds of discontinuities in high temperature supercondu... more A distributed circuit model for different kinds of discontinuities in high temperature superconducting (HTS) microstrip transmission lines (TLs), is proposed. In each case, closed form formula for lumped element model is presented based on the configuration of the discontinuity and the characterizations of HTS microstrip TLs. These discontinuities consist of steps in width, open ends, gaps and 90-degree bends. In the case of normal conductor microstrip TLs there are a lot of numerical and analytical equations that can accurately model them, however those formulas are not efficient for HTS TLs. Thus modified relations are extracted utilizing the superconducting characterizations to obtain much more accurate formulas. Additionally temperature dependence of HTS TLs is considered in the relations. Moreover regarding the kinetic inductance in HTS TLs a closed form formula is proposed for characteristic impedance of HTS TLs. Furthermore correction factors based on fringe fields is used to optimize all formulas. Using these formulations can lead to modeling and analysis of some superconducting microwave devices such as resonators, microwave filters, couplers, etc. In contrast to EM analysis, using the distributed circuit model is much easier for analysis of HTS microwave devices. The accuracy of the proposed model is confirmed in comparison with some electromagnetic full-wave simulations. This full analytical approach shows great accuracy in this test case as well.

Research paper thumbnail of Quasi Static Modeling of Weak Nonlinearity in Superconducting Transmission Lines with Sub-Wavelength Non-Uniformity

Physics Procedia, 2012

Superconducting passive microwave devices unlike routine normal conductor ones, due to dependence... more Superconducting passive microwave devices unlike routine normal conductor ones, due to dependence of superfluid density (n s) to current distribution, have a nonlinear behavior called Nonlinear Meissner Effect (NME). In this paper, a nonlinear distributed circuit model for HTS transmission lines with sub-wavelength longitudinal non-uniformity in the case of weak nonlinearity is proposed. This model is based on the quasi-TEM approximation of sub-wavelength non-uniform transmission lines (SW-NUTLs) that proposes closed form formulas for effective characteristic impedance and complex propagation constant of SW-NUTLs. Any NUTLs can be modeled with the mentioned method through dividing it into adequately small subsections to fulfill sub-wavelength condition. Regarding these propagation parameters relations, some effective equations for RLGC parameters are inferred. Because of dependence of the penetration depth and the real part of conductivity on n s , the proposed effective resistance and inductance depend on current distribution that in case of weak nonlinearity, follow a square-law form. As such the nonlinear microwave effects such as Intermodulation distortion (IMD) and harmonic generation can be calculated with harmonic balance (HB) Analysis. This semi-analytical approach shows great accuracy in different test cases.

Research paper thumbnail of Modeling of unusual nonlinear behaviors in superconducting microstrip transmission lines

Physica C: Superconductivity, 2013

There are unusual nonlinear behaviors in superconducting materials, especially at low temperature... more There are unusual nonlinear behaviors in superconducting materials, especially at low temperatures. This paper describes the procedure to reliably predict this nonlinearity in superconducting microstrip transmission lines (SMTLs). An accurate nonlinear distributed circuit model, based on simultaneously considering of both quadratic and modulus nonlinearity dependences, is proposed. All parameters of the equivalent circuit can be calculated analytically using proposed closed-form expressions. A numerical method based on Harmonic Balance approach is used to predict nonlinear phenomena like intermodulation distortions and third harmonic generations. Nonlinear analyses of the SMTLs at the different temperatures and the input powers have been presented. This proposed model can describe the unusual behaviors of the nonlinearity at low temperatures, which are frequently observed in the SMTLs.

Research paper thumbnail of Current Distribution and Nonlinearity of Open-Ends and Gaps in Superconducting Microstrip Structures

Journal of Superconductivity and Novel Magnetism, 2012

Research paper thumbnail of Superconducting Compact Coplanar Waveguide Filters Based on Quarter-Wavelength Spiral Resonators with Suppressed Slot-Line Mode

Electromagnetics, 2013

ABSTRACT Quarter-wavelength superconducting spiral resonators have been used to realize a coplana... more ABSTRACT Quarter-wavelength superconducting spiral resonators have been used to realize a coplanar waveguide bandpass filter and bandstop filter around the center frequency of 6 GHz. These compact coplanar waveguide filters have been made from 300-nm-thick NbTiN thin film on a 525-μm-thick silicon substrate. The bandpass filter is a six-pole Chebyshev filter with two zero transmissions due to nonadjacent coupling in its structure. Accurately microfabricated air-bridges have been used to suppress the undesired slot-line mode in this filter. The bandstop filter is a very simple two-pole structure that used wire bonding to suppress the slot-line mode. Measurements have been done at a temperature of 4.2 K in liquid helium. Good agreement between simulation and measurement results has been found.

Research paper thumbnail of On-chip filter bank spectroscopy at 600–700 GHz using NbTiN superconducting resonators

Applied Physics Letters, 2013

We experimentally demonstrate the principle of an on-chip submillimeter wave filter bank spectrom... more We experimentally demonstrate the principle of an on-chip submillimeter wave filter bank spectrometer, using superconducting microresonators as narrow band-separation filters. The filters are made of NbTiN/SiN x /NbTiN microstrip line resonators, which have a resonance frequency in the range of 614-685 GHz-two orders of magnitude higher in frequency than what is currently studied for use in circuit quantum electrodynamics and photodetectors. The frequency resolution of the filters decreases from 350 to 140 with increasing frequency, most likely limited by dissipation of the resonators.

Research paper thumbnail of Nonlinear Circuit Model for Discontinuity of Step in Width in Superconducting Microstrip Structures and Its Impact on Nonlinear Effects

IEEE Transactions on Applied Superconductivity, 2013

Superconducting materials are known to exhibit nonlinear effects and to produce harmonic generati... more Superconducting materials are known to exhibit nonlinear effects and to produce harmonic generation and intermodulation distortion in superconductive circuits. In planar structures, these nonlinearities depend on the current distribution on the strip which is mainly determined by the structure of the device. This paper investigates the current distribution at the step-in-width discontinuity in superconducting microstrip transmission lines, which is computed by a numerical approach based on a 3-D finite-element method. This current distribution is used to obtain the parameters of the nonlinear circuit model for the superconducting microstrip step-in-width discontinuity. The proposed equivalent nonlinear circuit can be solved using the harmonic balance method. Examples of two superconducting structures which contain the steps in width are given and validated by comparison with electromagnetic full-wave results. The proposed model can be used for effective optimization of the superconducting microwave filter resonators in order to minimize their nonlinear distortions.

Research paper thumbnail of Compensating the nonlinearity of laser diode in optical wireless transmission using OFDM

The nonlinear characteristic of an laser diode, LD, impacts on the performance of optical wireles... more The nonlinear characteristic of an laser diode, LD, impacts on the performance of optical wireless systems using OFDM (orthogonal frequency division multiplexing). First, the influence of the nonlinear characteristic on bit-error performance is analyzed using a high power LD (LML-808.7B-XX). Next, the paper proposes a predistorter to compensate the nonlinearities. Finally, the coherent optical OFDM (CO-OFDM) system is considered and the performance without linearization and after linearization is analyzed via simulations in an AWGN (additive white Gaussian noise) environment. It is shown that LD nonlinearity can significantly degrade the performance. However, it is demonstrated that this degradation can greatly be mitigated by using the proposed predistortion technique.

Research paper thumbnail of Modeling Nonlinearity in Superconducting Interdigital Capacitors and Its Effects on Metamaterial Structures

IEEE Transactions on Applied Superconductivity

Superconducting devices are known to indicate nonlinear behaviors such as harmonic generation and... more Superconducting devices are known to indicate nonlinear behaviors such as harmonic generation and intermodulation distortion even at low input powers. In this paper, a nonlinear equivalent circuit model for a superconducting interdigital capacitor (SIDC) is proposed. A numerical approach based on a 3-D finite-element method is used to compute the current distribution in SIDCs. Then, closed-form expressions for kinetic inductance, resistance, and geometrical nonlinear factor of SIDCs are proposed. The proposed model can be analyzed nonlinearly by using a harmonic balance method to predict nonlinear phenomena. To validate accuracy of the proposed nonlinear model, nonlinearity in a superconducting metamaterial structure consisting of two SIDCs is predicted. A good agreement between calculated results and measured ones was found. Thereafter, based on the proposed model, other nonlinear behaviors of the considered structures are predicted, and based on our new method, effects of nonlinearity on main parameters of the superconducting metamaterial structure such as phase constant, attenuation factor, plasma frequency, permittivity, and permeability are analyzed.

Research paper thumbnail of Superconducting Microstrip-Fed Antenna Coupled to a Microwave Kinetic Inductance Detector

A proper antenna to couple to a microstrip Microwave Kinetic Inductance Detector (MKID) is design... more A proper antenna to couple to a microstrip Microwave Kinetic Inductance Detector (MKID) is designed and simulated. A twinslot microstrip-fed inline antenna is designed for frequency band of 600720~GHz integrated with an elliptical lens and coupled to the MKID. A systematic design procedure for design of such antenna with microstrip inline feeding is presented. Whole structure of lens and twin slot is simulated by full-wave electromagnetic numerical software. A locally changing technique is also used to have good matching between antenna and feed line. Results show good radiation pattern with directivity near 30dB and side lobe levels better than -10.5 dB in both H-plane and Eplan and also antenna efficiency is better than 93% and total coupling efficiency is better than 84% in whole frequency band. This antenna is recently used in a superconducting on-chip sub-millimeter wave filterbank spectrometer.

Research paper thumbnail of Ultra High Q-Factor Superconducting Microresonator to Use in Microwave Kinetic Inductance Detectors

This article is focused on the design and development of superconducting Microwave Kinetic Induct... more This article is focused on the design and development of superconducting Microwave Kinetic Inductance Detector (MKID) which is used at near, mid and far-infrared, optical and ultraviolet wavelengths for astronomical applications. MKIDs are superconducting micro-resonators which are very much considered, due to high sensitivity, simplicity in fabrication and ease of read out by a coplanar waveguide or microstrip transmission line. Here a new structure for inductor of lumped element microwave resonator is proposed that causes a very high Quality factor in smaller dimensions. Our resonator's intrinsic Q factor is above 8×106in dimensions of 441×487 µm2which is the highest value in such dimensions. due to the small dimensions of this resonator, makes it desirable to use in large arrays spectrometers.

Research paper thumbnail of Modelling of current distribution and nonlinearity in superconducting coplanar waveguide (CPW) transmission line

Journal of Electromagnetic Waves and Applications

Research paper thumbnail of Nonlinearity in superconducting metamaterial structures, including spirally coupled lines

Physica C: Superconductivity and its Applications

Research paper thumbnail of Broadside Coupler Channels 1 To 10 GHz

Research paper thumbnail of Analysis of Nonlinearities in Superconducting Microstrip Straight Bends; FDTD Method in Comparison with Nonlinear Circuit Modeling

Journal of Superconductivity and Novel Magnetism, May 1, 2012

ABSTRACT This paper presents the prediction of nonlinearities in the superconducting microstrip s... more ABSTRACT This paper presents the prediction of nonlinearities in the superconducting microstrip straight bends in microwave frequencies based on two different methods; FDTD simulation as a numerical approach, and nonlinear circuit modeling as an analytical method. In the FDTD method, the superconducting microstrip structures are simulated with London’s equations. In the simulation, the penetration depth and normal conducting coefficient are considered as functions of current density of superconductor. To simulate the thin strip of superconductor, a non-uniform mesh has been used. For the nonlinear circuit modeling, we use distributed RLGC parameters for superconducting microstrip transmission lines. These parameters are considered as functions of the current distribution. This yields an equivalent nonlinear circuit model for bends. The final equivalent nonlinear circuit is analyzed using the harmonic balance (HB) method. Different straight bend structures have been considered and the two methods’ results are compared.

Research paper thumbnail of Nonlinearity in Symmetric and Asymmetric Superconducting Parallel-Coupled Microstrip Lines

Iet Microwaves Antennas Propagation, 2014

Research paper thumbnail of Analytical distributed non-linear model for symmetric and asymmetric superconducting parallel-coupled microstrip lines

IET Microwaves, Antennas & Propagation, 2014

ABSTRACT Superconducting materials are known to produce intermodulation distortion and other non-... more ABSTRACT Superconducting materials are known to produce intermodulation distortion and other non-linear effects. In microstrip structures, the non-linearity depends on the current distribution on the strip which is mainly determined by the geometrical structure of the device. The current distribution in superconducting parallel-coupled microstrip lines is computed by a numerical approach based on a three-dimensional finite element method. This computed current distribution is used to produce a non-linear circuit model for parallel-coupled superconducting lines. A numerical technique based on the harmonic balance approach is used for non-linear analysis of the proposed equivalent circuit. To validate the accuracy of the proposed model, the results of analysis of hairpin resonator superconducting band pass filters are compared with measured results. This proposed technique is useful for fast and efficient non-linear analysis of the superconducting microstrip coupled lines.

Research paper thumbnail of Broadband Omnidirectional and Miniature Fold-up Discone Antenna in VHF/UHF Band

Electromagnetics, Jul 5, 2012

ABSTRACT This article may be used for research, teaching, and private study purposes. Any substan... more ABSTRACT This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

Research paper thumbnail of Analysis of Nonlinearity in Step in Width Discontinuity of Superconducting Co-Planar Waveguide Structures

—In this paper, the nonlinearity in superconducting co-planar waveguides (SCPWs) with step in wid... more —In this paper, the nonlinearity in superconducting co-planar waveguides (SCPWs) with step in width discontinuities has been analyzed using a distributed nonlinear circuit model. In such structures, nonlinearities depend on the current distribution of the central strip of the SCPW. A numerical electromagnetics (EM) approach based on method of moment (MOM), which analyzes high frequency planar circuits, determines the current distribution. This is used to obtain the nonlinear circuit elements of a discontinued SCPW structure. The equivalent nonlinear circuit model can be solved using harmonic balance (HB) method as has been done in an example of a step in width SCPW. The accuracy of the model is shown by comparison of results with experiment for a SCPW transmission line structure. Moreover, all different types of step discontinuities in a SCPW have been compared and the efficient structure, which has the minimum nonlinearity has been defined.

Research paper thumbnail of Non-linearity in superconducting coplanar waveguide rectangular-spiral resonators

IET Microwaves, Antennas & Propagation, 2015

ABSTRACT In the present work, a non-linear distributed circuit model for superconducting rectangu... more ABSTRACT In the present work, a non-linear distributed circuit model for superconducting rectangular-spiral resonators is proposed. This is based on an accurate non-linear circuit model for superconducting parallel coupled lines, which is simultaneously considered both quadratic and modulus non-linear dependencies. The non-linearity in superconducting devices depends on the current distribution, which is mainly determined by the geometrical structure of the device. The current distribution in the superconducting spiral resonators can be computed by a numerical approach based on three-dimensional finite element method. This computed current distribution is used to produce a non-linear circuit model for the superconducting spiral resonator. Numerical technique based on harmonic balance approach is used for non-linear analysis of the proposed equivalent non-linear circuit. The model is proposed for coplanar waveguide (CPW) resonators, which can easily be extended for microstrip resonators. To confirm the accuracy of the proposed model, non-linearity in a 6-pole superconducting CPW spiral bandpass filter has been measured. Measurement results show good agreement with the ones from the model. This proposed technique is found to be a major approach for fast and efficient non-linear analysis of the superconducting spiral resonators and filters.

Research paper thumbnail of Closed Form Formulas for Distributed Circuit Model of Discontinuities in HTS Microstrip Transmission Lines

Physics Procedia, 2012

A distributed circuit model for different kinds of discontinuities in high temperature supercondu... more A distributed circuit model for different kinds of discontinuities in high temperature superconducting (HTS) microstrip transmission lines (TLs), is proposed. In each case, closed form formula for lumped element model is presented based on the configuration of the discontinuity and the characterizations of HTS microstrip TLs. These discontinuities consist of steps in width, open ends, gaps and 90-degree bends. In the case of normal conductor microstrip TLs there are a lot of numerical and analytical equations that can accurately model them, however those formulas are not efficient for HTS TLs. Thus modified relations are extracted utilizing the superconducting characterizations to obtain much more accurate formulas. Additionally temperature dependence of HTS TLs is considered in the relations. Moreover regarding the kinetic inductance in HTS TLs a closed form formula is proposed for characteristic impedance of HTS TLs. Furthermore correction factors based on fringe fields is used to optimize all formulas. Using these formulations can lead to modeling and analysis of some superconducting microwave devices such as resonators, microwave filters, couplers, etc. In contrast to EM analysis, using the distributed circuit model is much easier for analysis of HTS microwave devices. The accuracy of the proposed model is confirmed in comparison with some electromagnetic full-wave simulations. This full analytical approach shows great accuracy in this test case as well.

Research paper thumbnail of Quasi Static Modeling of Weak Nonlinearity in Superconducting Transmission Lines with Sub-Wavelength Non-Uniformity

Physics Procedia, 2012

Superconducting passive microwave devices unlike routine normal conductor ones, due to dependence... more Superconducting passive microwave devices unlike routine normal conductor ones, due to dependence of superfluid density (n s) to current distribution, have a nonlinear behavior called Nonlinear Meissner Effect (NME). In this paper, a nonlinear distributed circuit model for HTS transmission lines with sub-wavelength longitudinal non-uniformity in the case of weak nonlinearity is proposed. This model is based on the quasi-TEM approximation of sub-wavelength non-uniform transmission lines (SW-NUTLs) that proposes closed form formulas for effective characteristic impedance and complex propagation constant of SW-NUTLs. Any NUTLs can be modeled with the mentioned method through dividing it into adequately small subsections to fulfill sub-wavelength condition. Regarding these propagation parameters relations, some effective equations for RLGC parameters are inferred. Because of dependence of the penetration depth and the real part of conductivity on n s , the proposed effective resistance and inductance depend on current distribution that in case of weak nonlinearity, follow a square-law form. As such the nonlinear microwave effects such as Intermodulation distortion (IMD) and harmonic generation can be calculated with harmonic balance (HB) Analysis. This semi-analytical approach shows great accuracy in different test cases.

Research paper thumbnail of Modeling of unusual nonlinear behaviors in superconducting microstrip transmission lines

Physica C: Superconductivity, 2013

There are unusual nonlinear behaviors in superconducting materials, especially at low temperature... more There are unusual nonlinear behaviors in superconducting materials, especially at low temperatures. This paper describes the procedure to reliably predict this nonlinearity in superconducting microstrip transmission lines (SMTLs). An accurate nonlinear distributed circuit model, based on simultaneously considering of both quadratic and modulus nonlinearity dependences, is proposed. All parameters of the equivalent circuit can be calculated analytically using proposed closed-form expressions. A numerical method based on Harmonic Balance approach is used to predict nonlinear phenomena like intermodulation distortions and third harmonic generations. Nonlinear analyses of the SMTLs at the different temperatures and the input powers have been presented. This proposed model can describe the unusual behaviors of the nonlinearity at low temperatures, which are frequently observed in the SMTLs.

Research paper thumbnail of Current Distribution and Nonlinearity of Open-Ends and Gaps in Superconducting Microstrip Structures

Journal of Superconductivity and Novel Magnetism, 2012

Research paper thumbnail of Superconducting Compact Coplanar Waveguide Filters Based on Quarter-Wavelength Spiral Resonators with Suppressed Slot-Line Mode

Electromagnetics, 2013

ABSTRACT Quarter-wavelength superconducting spiral resonators have been used to realize a coplana... more ABSTRACT Quarter-wavelength superconducting spiral resonators have been used to realize a coplanar waveguide bandpass filter and bandstop filter around the center frequency of 6 GHz. These compact coplanar waveguide filters have been made from 300-nm-thick NbTiN thin film on a 525-μm-thick silicon substrate. The bandpass filter is a six-pole Chebyshev filter with two zero transmissions due to nonadjacent coupling in its structure. Accurately microfabricated air-bridges have been used to suppress the undesired slot-line mode in this filter. The bandstop filter is a very simple two-pole structure that used wire bonding to suppress the slot-line mode. Measurements have been done at a temperature of 4.2 K in liquid helium. Good agreement between simulation and measurement results has been found.

Research paper thumbnail of On-chip filter bank spectroscopy at 600–700 GHz using NbTiN superconducting resonators

Applied Physics Letters, 2013

We experimentally demonstrate the principle of an on-chip submillimeter wave filter bank spectrom... more We experimentally demonstrate the principle of an on-chip submillimeter wave filter bank spectrometer, using superconducting microresonators as narrow band-separation filters. The filters are made of NbTiN/SiN x /NbTiN microstrip line resonators, which have a resonance frequency in the range of 614-685 GHz-two orders of magnitude higher in frequency than what is currently studied for use in circuit quantum electrodynamics and photodetectors. The frequency resolution of the filters decreases from 350 to 140 with increasing frequency, most likely limited by dissipation of the resonators.

Research paper thumbnail of Nonlinear Circuit Model for Discontinuity of Step in Width in Superconducting Microstrip Structures and Its Impact on Nonlinear Effects

IEEE Transactions on Applied Superconductivity, 2013

Superconducting materials are known to exhibit nonlinear effects and to produce harmonic generati... more Superconducting materials are known to exhibit nonlinear effects and to produce harmonic generation and intermodulation distortion in superconductive circuits. In planar structures, these nonlinearities depend on the current distribution on the strip which is mainly determined by the structure of the device. This paper investigates the current distribution at the step-in-width discontinuity in superconducting microstrip transmission lines, which is computed by a numerical approach based on a 3-D finite-element method. This current distribution is used to obtain the parameters of the nonlinear circuit model for the superconducting microstrip step-in-width discontinuity. The proposed equivalent nonlinear circuit can be solved using the harmonic balance method. Examples of two superconducting structures which contain the steps in width are given and validated by comparison with electromagnetic full-wave results. The proposed model can be used for effective optimization of the superconducting microwave filter resonators in order to minimize their nonlinear distortions.

Research paper thumbnail of Compensating the nonlinearity of laser diode in optical wireless transmission using OFDM

The nonlinear characteristic of an laser diode, LD, impacts on the performance of optical wireles... more The nonlinear characteristic of an laser diode, LD, impacts on the performance of optical wireless systems using OFDM (orthogonal frequency division multiplexing). First, the influence of the nonlinear characteristic on bit-error performance is analyzed using a high power LD (LML-808.7B-XX). Next, the paper proposes a predistorter to compensate the nonlinearities. Finally, the coherent optical OFDM (CO-OFDM) system is considered and the performance without linearization and after linearization is analyzed via simulations in an AWGN (additive white Gaussian noise) environment. It is shown that LD nonlinearity can significantly degrade the performance. However, it is demonstrated that this degradation can greatly be mitigated by using the proposed predistortion technique.

Research paper thumbnail of Modeling Nonlinearity in Superconducting Interdigital Capacitors and Its Effects on Metamaterial Structures

IEEE Transactions on Applied Superconductivity

Superconducting devices are known to indicate nonlinear behaviors such as harmonic generation and... more Superconducting devices are known to indicate nonlinear behaviors such as harmonic generation and intermodulation distortion even at low input powers. In this paper, a nonlinear equivalent circuit model for a superconducting interdigital capacitor (SIDC) is proposed. A numerical approach based on a 3-D finite-element method is used to compute the current distribution in SIDCs. Then, closed-form expressions for kinetic inductance, resistance, and geometrical nonlinear factor of SIDCs are proposed. The proposed model can be analyzed nonlinearly by using a harmonic balance method to predict nonlinear phenomena. To validate accuracy of the proposed nonlinear model, nonlinearity in a superconducting metamaterial structure consisting of two SIDCs is predicted. A good agreement between calculated results and measured ones was found. Thereafter, based on the proposed model, other nonlinear behaviors of the considered structures are predicted, and based on our new method, effects of nonlinearity on main parameters of the superconducting metamaterial structure such as phase constant, attenuation factor, plasma frequency, permittivity, and permeability are analyzed.

Research paper thumbnail of Superconducting Microstrip-Fed Antenna Coupled to a Microwave Kinetic Inductance Detector

A proper antenna to couple to a microstrip Microwave Kinetic Inductance Detector (MKID) is design... more A proper antenna to couple to a microstrip Microwave Kinetic Inductance Detector (MKID) is designed and simulated. A twinslot microstrip-fed inline antenna is designed for frequency band of 600720~GHz integrated with an elliptical lens and coupled to the MKID. A systematic design procedure for design of such antenna with microstrip inline feeding is presented. Whole structure of lens and twin slot is simulated by full-wave electromagnetic numerical software. A locally changing technique is also used to have good matching between antenna and feed line. Results show good radiation pattern with directivity near 30dB and side lobe levels better than -10.5 dB in both H-plane and Eplan and also antenna efficiency is better than 93% and total coupling efficiency is better than 84% in whole frequency band. This antenna is recently used in a superconducting on-chip sub-millimeter wave filterbank spectrometer.

Research paper thumbnail of Ultra High Q-Factor Superconducting Microresonator to Use in Microwave Kinetic Inductance Detectors

This article is focused on the design and development of superconducting Microwave Kinetic Induct... more This article is focused on the design and development of superconducting Microwave Kinetic Inductance Detector (MKID) which is used at near, mid and far-infrared, optical and ultraviolet wavelengths for astronomical applications. MKIDs are superconducting micro-resonators which are very much considered, due to high sensitivity, simplicity in fabrication and ease of read out by a coplanar waveguide or microstrip transmission line. Here a new structure for inductor of lumped element microwave resonator is proposed that causes a very high Quality factor in smaller dimensions. Our resonator's intrinsic Q factor is above 8×106in dimensions of 441×487 µm2which is the highest value in such dimensions. due to the small dimensions of this resonator, makes it desirable to use in large arrays spectrometers.

Research paper thumbnail of Modelling of current distribution and nonlinearity in superconducting coplanar waveguide (CPW) transmission line

Journal of Electromagnetic Waves and Applications

Research paper thumbnail of Nonlinearity in superconducting metamaterial structures, including spirally coupled lines

Physica C: Superconductivity and its Applications

Research paper thumbnail of Broadside Coupler Channels 1 To 10 GHz

Research paper thumbnail of Analysis of Nonlinearities in Superconducting Microstrip Straight Bends; FDTD Method in Comparison with Nonlinear Circuit Modeling

Journal of Superconductivity and Novel Magnetism, May 1, 2012

ABSTRACT This paper presents the prediction of nonlinearities in the superconducting microstrip s... more ABSTRACT This paper presents the prediction of nonlinearities in the superconducting microstrip straight bends in microwave frequencies based on two different methods; FDTD simulation as a numerical approach, and nonlinear circuit modeling as an analytical method. In the FDTD method, the superconducting microstrip structures are simulated with London’s equations. In the simulation, the penetration depth and normal conducting coefficient are considered as functions of current density of superconductor. To simulate the thin strip of superconductor, a non-uniform mesh has been used. For the nonlinear circuit modeling, we use distributed RLGC parameters for superconducting microstrip transmission lines. These parameters are considered as functions of the current distribution. This yields an equivalent nonlinear circuit model for bends. The final equivalent nonlinear circuit is analyzed using the harmonic balance (HB) method. Different straight bend structures have been considered and the two methods’ results are compared.

Research paper thumbnail of Nonlinearity in Symmetric and Asymmetric Superconducting Parallel-Coupled Microstrip Lines

Iet Microwaves Antennas Propagation, 2014

Research paper thumbnail of Analytical distributed non-linear model for symmetric and asymmetric superconducting parallel-coupled microstrip lines

IET Microwaves, Antennas & Propagation, 2014

ABSTRACT Superconducting materials are known to produce intermodulation distortion and other non-... more ABSTRACT Superconducting materials are known to produce intermodulation distortion and other non-linear effects. In microstrip structures, the non-linearity depends on the current distribution on the strip which is mainly determined by the geometrical structure of the device. The current distribution in superconducting parallel-coupled microstrip lines is computed by a numerical approach based on a three-dimensional finite element method. This computed current distribution is used to produce a non-linear circuit model for parallel-coupled superconducting lines. A numerical technique based on the harmonic balance approach is used for non-linear analysis of the proposed equivalent circuit. To validate the accuracy of the proposed model, the results of analysis of hairpin resonator superconducting band pass filters are compared with measured results. This proposed technique is useful for fast and efficient non-linear analysis of the superconducting microstrip coupled lines.

Research paper thumbnail of Broadband Omnidirectional and Miniature Fold-up Discone Antenna in VHF/UHF Band

Electromagnetics, Jul 5, 2012

ABSTRACT This article may be used for research, teaching, and private study purposes. Any substan... more ABSTRACT This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

Research paper thumbnail of Analysis of Nonlinearity in Step in Width Discontinuity of Superconducting Co-Planar Waveguide Structures

—In this paper, the nonlinearity in superconducting co-planar waveguides (SCPWs) with step in wid... more —In this paper, the nonlinearity in superconducting co-planar waveguides (SCPWs) with step in width discontinuities has been analyzed using a distributed nonlinear circuit model. In such structures, nonlinearities depend on the current distribution of the central strip of the SCPW. A numerical electromagnetics (EM) approach based on method of moment (MOM), which analyzes high frequency planar circuits, determines the current distribution. This is used to obtain the nonlinear circuit elements of a discontinued SCPW structure. The equivalent nonlinear circuit model can be solved using harmonic balance (HB) method as has been done in an example of a step in width SCPW. The accuracy of the model is shown by comparison of results with experiment for a SCPW transmission line structure. Moreover, all different types of step discontinuities in a SCPW have been compared and the efficient structure, which has the minimum nonlinearity has been defined.