Microwave Circuits Research Articles

Surrogate based design optimization of low noise amplifier for ISM band

Design optimization of microwave circuits is a crucial matter for microwave engineers. For the last decades, researchers had been studying surrogate models for a computationally efficient design optimization process. Artificial Intelligence based algorithms had been used for modelling of complex microwave stages such as antenna, amplifiers and frequency selective surfaces. In this study, design optimization of a Low Noise Amplifier (LNA) based on surrogate models for both transistor stage and input & output matching circuits had been presented. Support Vector Regression Machine had been used for creating surrogate models of a microwave transistor and a non-uniform transmission line for having a fast and accurate LNA design optimization process alongside a low profile and high performance LNA using on-uniform transmission lines. By using this methodology, not only designer can create a mapping for missing points in the sparse sample S parameter data points provided by manufacturers but also the overall simulation duration can be significantly reduced thanks to the fast nature of surrogates compared to EM simulators. Here, the proposed surrogate models had been used alongside of Particle Swarm Optimization algorithm to determine optimal geometrical values of input/output matching networks. Then the obtained designs are prototyped and measured. The measured results are also compared with the performance results of counterpart design in literature. As for results, not only the proposed methodology is an effective, fast and reliable method for computationally efficient design optimization process of LNA but also provides better results than the counterpart design in literature.

Microwave Resonant Spectroscopy of Semiconductors with Micrometer Resolution

We have proposed and experimentally verified a local method of microwave resonant spectroscopy of semiconductors. The microwave circuit of the spectrometer based on the Cascade Microtech probe station is equipped with a coaxial resonator of special geometry. As result, the measurement accuracy of the previously developed volt-impedance spectroscopy method was greatly increased. A technique for spectrometer calibration and resonant measurements of the complex impedance of the probe-sample system has been developed. We have measured the impedance of test structures with Schottky contacts of 30-60 μm in diameter on a single-crystal GaAs wafer at several discrete frequencies in the range of 50-250 MHz. The nontrivial resistive properties of the structures are studied, which consist of the excess resistance that is 1-2 orders higher than the spreading resistance for the alternating current in the unperturbed region of the semiconductor. The discovered effect is presumably associated with the a.c. charge modulation on deep levels of the semiconductor. A model calculation of the impedance spectrum has been performed, which demonstrates a good agreement with the experimental spectra. Keywords: Microwave microscope, near field, probe, resonator, impedance, semiconductor.

A Novel Balanced-to-balanced Differential-mode Negative Group Delay Microwave Circuit with Excellent Common-mode Suppression

A Novel Balanced-to-balanced Differential-mode Negative Group Delay Microwave Circuit with Excellent Common-mode Suppression

Microwave Resonant Spectroscopy of Semiconductors with MicrometerResolution

We have proposed and experimentally verified a local method ofmicrowave resonant spectroscopy of semiconductors. The microwave circuit ofthe spectrometer based on the Cascade Microtech probe station is equippedwith a coaxial resonator of special geometry. As result, the measurementaccuracy of the previously developed volt-impedance spectroscopy method wasgreatly increased. A technique for spectrometer calibration and resonantmeasurements of the complex impedance of the probe-sample system has beendeveloped. We have measured the impedance of test structures with Schottkycontacts of 30-60 μm in diameter on a single-crystal GaAs wafer at severaldiscrete frequencies in the range of 50-250 MHz . The nontrivial resistiveproperties of the structures are studied, which consist of the excessresistance that is 1-2 orders higher than the spreading resistance for thealternating current in the unperturbed region of the semiconductor. Thediscovered effect is presumably associated with the a.c. charge modulationon deep levels of the semiconductor. A model calculation of the impedancespectrum has been performed, which demonstrates a good agreement with theexperimental spectra. Keywords: Microwave microscope, near field, probe, resonator, impedance, semiconductor.\

Design Centering of Compact Microwave Components Using Response Features and Trust Regions

Fabrication tolerances, as well as uncertainties of other kinds, e.g., concerning material parameters or operating conditions, are detrimental to the performance of microwave circuits. Mitigating their impact requires accounting for possible parameter deviations already at the design stage. This involves optimization of appropriately defined statistical figures of merit such as yield. Although important, robust (or tolerance-aware) design is an intricate endeavor because manufacturing inaccuracies are normally described using probability distributions, and their quantification has to be based on statistical analysis. The major bottleneck here is high computational cost: for reliability reasons, miniaturized microwave components are evaluated using full-wave electromagnetic (EM) models, whereas conventionally utilized analysis methods (e.g., Monte Carlo simulation) are associated with massive circuit evaluations. A practical approach that allows for circumventing the aforementioned obstacles offers surrogate modeling techniques, which have been a dominant trend over the recent years. Notwithstanding, a construction of accurate metamodels may require considerable computational investments, especially for higher-dimensional cases. This paper brings in a novel design-centering approach, which assembles forward surrogates founded at the level of response features and trust-region framework for direct optimization of the system yield. Formulating the problem with the use of characteristic points of the system response alleviates the issues related to response nonlinearities. At the same time, as the surrogate is a linear regression model, a rapid yield estimation is possible through numerical integration of the input probability distributions. As a result, expenditures related to design centering equal merely few dozens of EM analyses. The introduced technique is demonstrated using three microstrip couplers. It is compared to recently reported techniques, and its reliability is corroborated using EM-based Monte Carlo analysis.

Discussion and Analysis of Dumbbell Defect-Ground-Structure (DB-DGS) Resonators for Sensing Applications from a Circuit Theory Perspective.

Microstrip transmission lines loaded with dumbbell defect-ground-structure (DB-DGS) resonators transversally oriented have been exhaustively used in microwave circuits and sensors. Typically, these structures have been modelled by means of a parallel LC resonant tank series connected to the host line. However, the inductance and capacitance of such model do not have a physical meaning, since this model is inferred by transformation of a more realistic model, where the DB-DGS resonator, described by means of a resonant tank with inductance and capacitance related to the geometry of the DB-DGS, is magnetically coupled to the host line. From parameter extraction, the circuit parameters of both models are obtained by considering the DB-DGS covered with semi-infinite materials with different dielectric constant. The extracted parameters are coherent and reveal that the general assumption of considering the simple LC resonant tank series-connected to the line to describe the DB-DGS-loaded line is reasonable with some caution. The implications on the sensitivity, when the structure is devoted to operating as a permittivity sensor, are discussed.

Enhanced Performance of Multilayer Bandpass Filter Using Slow-Wave Empty Substrate- Integrated Waveguide (SW-ESIW)

In this letter, two compact and high-performance filters based on multilayer slow-wave empty substrate-integrated waveguide (SW-ESIW) are presented. SW-ESIW, which contains the air cavity and a bottom layer including several rows of internal metallized via holes, provides a compromise between insertion loss and footprint. It is the first time that SW-ESIW is used to implement compact filters with multilayer air cavity. The proposed filters are simulated, fabricated, and measured. The measurements are consistent with simulations, indicating that the proposed filters can be reduced more than 35% in dimension compared to the same filters in ESIW. Based on the SW-ESIW technology, the proposed multilayer filters realize the advantages of low insertion loss and miniaturization, and express the tremendous potential on applications to complex and high-performance microwave circuits and systems.

Strain-engineering in AlGaN/GaN HEMTs: impact of silicon nitride passivation layer on electrical performance

In this work, we present a physics-based analysis of two-dimensional electron gas (2DEG) sheet carrier density and other microwave characteristics such as transconductance and cutoff frequency of AlxGa1−xN/GaN high electron mobility transistors (HEMT). An accurate polarization-dependent charge control-based analysis is performed for microwave performance assessment in terms of current, transconductance, gate capacitances, and cutoff frequency of lattice-mismatched AlGaN/GaN HEMTs. The influence of stress on spontaneous and piezoelectric polarization is included in the simulation of an AlGaN/GaN HEMT. We have shown the change in threshold voltage (Vt) due to tensile and compressive strain with different gate lengths. Also, the influence of stress due to the change in nitride thickness is presented. Our simulation results for drain current, transconductance, and current-gain cutoff frequency for various gate length devices are calibrated and verified with experimental data over a wide range of gate and drain applied voltages, which are expected to be useful for microwave circuit design. The predicted transconductance, drain conductance, and operation frequency are quite close to the experimental data. The AlGaN/GaN heterostructure HEMTs with nitride passivation layers show great promise as a candidate in future high speed and high power applications.

Wideband and high-order microwave vortex-beam launcher based on spoof surface plasmon polaritons

The electromagnetic vortex carrying orbital angular momentum (OAM), which is first studied at optical frequency, has begun to attract widespread attention in the field of radio-frequency/microwave. However, for the OAM mode generated by traditional single antennas, there are problems such as low order and narrow bandwidth, and complex structures such as dual-fed networks may be required. In this paper, based on spoof surface plasmon polariton (SSPP) mode leaky-wave antenna, a single-port traveling-wave ring is proposed to radiate high-order OAM modes working near the cut-off frequency of SSPP state. The achieved 12-order OAM mode within 9.1–10.1 GHz (relative bandwidth of 10.4%) has the main radiation direction close to the antenna surface, forming a plane spiral OAM (PSOAM) wave, which reduces the requirements for mode purity in practical applications. This SSPP ring using periodic units as radiating elements can be an effective radiator for broadband and large-capacity OAM multiplexing communications. The structural characteristics of single feed contribute to the integration of microwave circuits.

Математична модель антени з нелінійними характеристиками для розрахунку елект-ромагнітного поля у зоні Френеля

The paper presents a mathematical model of radio-electronic systems (RES), which include antennas and their excitation paths with nonlinear characteristics. The model provides acceptable accuracy of RES quality indicator analysis and electromagnetic compatibility (EMC) for further practical design. General purpose: the development of a mathematical model of a transmitting multi-input radiating structure with nonlinear characteristics under the Fresnel zone. Objective: choice justification of a structural schema of a radiating multi-input system with a radiator that has a distributed nonlinear surface impedance; obtaining the nonlinear integral equations (NIE) related to the current density for radiators with distributed nonlinearity, excited by an arbitrary field distribution for solving the general analysis problem; obtaining a ratio for calculating focused electromagnetic fields (EMF) created by multi-input radiating structures with nonlinear characteristics in the Fresnel zone. The methods used in the paper are mathematical methods of electrodynamics and antennas theory with nonlinear elements (ANE), theory of microwave circuits, and multipoles. The following results were obtained. An electrodynamics approach is proposed to analyze the entire set of nonlinear effects arising in transmitting multi-input radiating structures with nonlinear characteristics. It allows considering the mutual influence of the transmitting and receiving antennas with nonlinear characteristics in the system itself and the electrodynamics interaction of the transmitting antenna with nonlinear characteristics with RES for other purposes. Component equations (NIE) of multi-input radiating structures that establish the relationship of amplitude-phase distribution at the inputs of radiators with distributed nonlinearity and amplitude-phase distribution on their surfaces are obtained. A mathematical model of multi-input radiator structures with nonlinear characteristics in the Fresnel zone for analysis purposes has been produced. Conclusions. The scientific novelty of the obtained results is as follows: a generalized theory of transmitting antennas of arbitrary configuration with nonlinear characteristics in the Fresnel zone, which makes it possible to analyze the characteristics of these antennas considering the positive and negative (beneficial and adverse) nonlinear effects that arise in them.

Optimization of the SIW cavity-backed slots antenna for X-band applications using the Particle Swarm Optimization algorithm

Substrate Integrated Waveguide (SIW) technology has recently drawn attention to its microwave benefits, such as integration into planar microwave circuits, low manufacturing cost and high-quality factor compared to other voluminous technologies. In this paper, a cavity-backed slot antenna structure has been designed and optimised by the Particle Swarm Optimization (PSO) algorithm and manufactured for X-band applications. Indeed, the starting cavity-backed slot antenna has three pairs of resonators placed on the lower wall of the cavity, and the PSO algorithm seeks the optimal antenna by automating HFSS using MATLAB script. Two antennas have been chosen from the last PSO generation. The selected antennas operate respectively on the bands [9.17 GHz. 10.63 GHz] and [9.09 GHz, 10.6 GHz] with a bandwidth of 15%, and can achieve a maximum gain of 8.8 dBi. The total size of the proposed design is . The gain, reflection coefficient and radiation partners are measured and compared to the EM simulation results and a very good agreement is obtained.

Laser-Scribed Graphene (LSG) Fabrication Method for Microwave Circuit Applications

In this letter, a laser-scribed graphene (LSG) fabrication method is used to create graphene to be used in a microwave application, for example, a voltage-tunable microstrip attenuator. Graphene used in microwave circuits, such as tunable attenuators, usually focuses on using exfoliated graphene, deposited graphene nanoplatelets, or microwave irradiation. It will be demonstrated that the fabrication of LSG from graphene oxide on standard double-sided FR-4 copper-clad substrate can be used as a voltage-controlled resistor that results in a tunable microstrip attenuator across the microwave frequencies from 50 MHz to 5.5 GHz.

A 2.0-GHz compact ESR spectrometer for monitoring automobile lubrication oil degradation

This article reports a simple, compact, and cost-effective electron spin resonance (ESR) spectrometer for monitoring automobile lubrication oil degradation. Lubrication oil degradation strongly correlates with the concentration of stable free radicals caused by hydrocarbon chain decomposition due to heating. For the prototype spectrometer, the amplitude shift in a marginal oscillator output detects ESR absorption in a sample. The spectrometer’s spin sensitivity of 2.3 × 1014 spins for a used oil sample was achieved using the marginal oscillator with a loop-gap resonator. For the prototype spectrometer, the oscillation frequency was 2.09 GHz. The volume of the prototype spectrometer was 1.3 L, including a permanent magnet, microwave circuits, and digital communication circuitry on printed circuit boards. The weight of the spectrometer setup was 1.45 kg. This prototype spectrometer successfully detected the ESR signal from a 50 μL oil sample (spin concentration 8.3 x1019 spins/L) with a signal-to-noise ratio of 37 and an acquisition time of 30 s.

Lumped-Network FDTD Method for Simulating Transient Responses of RF Amplifiers Excited by Intentional Electromagnetic Interference Signals

Unintentional as well as intentional electromagnetic interference can cause interference and performance degradation of microwave circuits or systems. In this article, a modified multiport lumped-network finite-difference time-domain method (FDTD) method based on Y-matrix is proposed, where bilinear transform is used to incorporate the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V–I</i> relation of the lumped-network into FDTD iteration. It is further used for simulating transient responses of <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mesfet</small> -based amplifiers, which are often used in many radar and communication systems. The excitation of such an RF amplifier is assumed to be an intentional electromagnetic interference (IEMI) signal but with different waveforms and magnitudes. Parametric studies are performed to show hybrid effects of waveforms and magnitudes of the IEMI signals on the transient coupled voltages at the output port of such <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mesfet</small> -based amplifier, with useful information obtained for understanding the interaction process between the intentional electromagnetic interference signals and active components.

Efficient electromagnetic transducers for spin-wave devices

This paper presents a system-level efficiency analysis, a rapid design methodology, and a numerical demonstration of efficient sub-micron, spin-wave transducers in a microwave system. Applications such as Boolean spintronics, analog spin-wave-computing, and magnetic microwave circuits are expected to benefit from this analysis and design approach. These applications have the potential to provide a low-power, magnetic paradigm alternative to modern electronic systems, but they have been stymied by a limited understanding of the microwave, system-level design for spin-wave circuits. This paper proposes an end-to-end microwave/spin-wave system model that permits the use of classical microwave network analysis and matching theory towards analyzing and designing efficient transduction systems. This paper further compares magnetostatic-wave transducer theory to electromagnetic simulations and finds close agreement, indicating that the theory, despite simplifying assumptions, is useful for rapid yet accurate transducer design. It further suggests that the theory, when modified to include the exchange interaction, will also be useful to rapidly and accurately design transducers launching magnons at exchange wavelengths. Comparisons are made between microstrip and co-planar waveguide lines, which are expedient, narrowband, and low-efficiency transducers, and grating and meander lines that are capable of high-efficiency and wideband performance. The paper concludes that efficient microwave-to-spin-wave transducers are possible and presents a meander transducer design on YIG capable of launching varvec{lambda = 500},nm spin waves with an efficiency of − 4.45 dB and a 3 dB-bandwidth of 134 MHz.

Dielectric absorption correlated to ferromagnetic behavior in (Cr, Ni)-codoped 4H–SiC for microwave applications

For (Cr, Ni)-codoped 4H silicon carbide SiC, electronic/optical properties are calculated, and a ferromagnetic (FM) order is detected. Doping Ni at Si sites should not destroy the effective coupling of the spins induced by Cr, could enormously boost the quality of absorbing electromagnetic waves, and acts as resist coatings for Cr-doped 4H-SiC. The metallic character shown by (Ni, Cr)-codoped 4H–SiC allow us using it in microwave circuits. Its FM order is mainly due to Cr impurities, so that the strong FM coupling originates from p-d hybridization interaction. Our results show that substituting Al for Ni either in (Al, Cr) or (Al, Cr)-doped 4H-SiC may improve the magnetism of 4H–SiCand enhance its microwave absorbing properties in the mm-wave band.

Matter waves, single-mode excitations of the matter-wave field, and the atomtronic transistor oscillator

A self-consistent theoretical treatment of a triple-well atomtronic transistor circuit reveals the mechanism of gain, conditions of oscillation, and properties of the subsequent coherent matterwaves emitted by the circuit. A Bose-condensed reservoir of atoms in a large source well provides a chemical potential that drives circuit dynamics. The theory is based on the ansatz that a condensate arises in the transistor gate well as a displaced ground state, that is, one that undergoes dipole oscillation in the well. That gate atoms remain condensed and oscillating is shown to be a consequence of the cooling induced by the emission of a matterwave into the vacuum. Key circuit parameters such as the transistor transconductance and output current are derived by transitioning to a classical equivalent circuit model. Voltage-like and current-like matterwave circuit wave fields are introduced in analogy with microwave circuits, as well as an impedance relationship between the two. This leads to a new notion of a classical coherent matterwave that is the dual of a coherent electromagnetic wave and which is distinct from a deBroglie matterwave associated with cold atoms. Subjecting the emitted atom flux to an atomic potential that will reduce the deBroglie wavelength, for example, will increase the classical matterwave wavelength. Quantization of the classical matterwave fields leads to the dual of the photon that is identified not as an atom but as something else, which is here dubbed a "matteron".

Very large group delay in VHF band using coupled high temperature superconducting resonators

Storing a very high frequency (VHF) band (30–300 MHz) electromagnetic wave has many potential applications, such as phase modulation, buffering, and radio frequency memory. It can be effectively achieved by applying coupled resonator-based electromagnetically induced transparency (EIT) due to its slow light effect. However, the wavelength in the VHF band is too long to design resonators, and the group delay is limited by the high resistive loss of metal. The practical application of EIT in the VHF band is still a big challenge. In this work, we propose and experimentally demonstrate EIT response in a high-temperature superconducting (HTS) microwave circuit with coupled-resonator-induced transparency. The chip size of the HTS circuit is only 34 mm × 20 mm with a very low transparency frequency of 198.55 MHz. In addition, we implement very large group delay higher than 12.3 μs and 16.2 μs with working temperatures of 65 K and 50 K separately, which is much longer than the previous reported works on slow wave. The fabricated circuit is planar with working temperature about 65 K, and thus can be easily integrated into other microwave devices under the cryogenic conditions provided by a commercial portable Stirling cryocooler. Our proposed method paves a way for studying EIT in the microwave region due to the high quality factor of the HTS resonator, which has great potential use for radio-frequency memory in the future.

Dielectric Characterization of Anisotropic 3D-Printed Biodegradable Substrates Based on Polylactic Acid [Application Notes

3D-printed dielectric substrates are manufactured using additive manufacturing (AM) technology. With CAD/CAM, rapid, accurate, and automatic manufacturing of objects with different characteristics and almost any geometry is possible. With 3D printing processes, objects are formed layer by layer, and complicated shapes can easily be created. For this reason, in the last decade, AM has seen a great boom in the development of RF and microwave circuits. Some applications that benefit from AM are metamaterials [1]-[3], antennas [4]-[5], and selective surfaces [6], among others. Most of the RF and microwave circuits reported in previous works are designed considering the dielectric substrate as an isotropic material; therefore, large differences are found between the measured and the simulated results [6]-[8]. These variations are largely due to the fact that the manufacturing standards generally include a mixture of materials inside the substrates with a periodic arrangement [9], and this favors dielectric anisotropy in the substrates. Consequently, the study of these materials is of great importance to the scientific community. This article is intended for designers who wish to tailor the dielectric characteristics of a substrate for microwave circuits, noting that anisotropy will manifest itself at lower frequencies when the internal structure of the printed material is modified.

Low microwave loss in deposited Si and Ge thin-film dielectrics at single-photon power and low temperatures

In this study, we show that deposited Ge and Si dielectric thin-films can exhibit low microwave losses at single-photon powers and sub-Kelvin temperatures (≈40 mK). This low loss enables their use in a wide range of devices, including coplanar, microstrip, and stripline resonators, as well as layers for device isolation, interwiring dielectrics, and passivation in microwave and Josephson junction circuit fabrication. We use coplanar microwave resonator structures with narrow trace widths and minimal over-etch to maximize the sensitivity of loss tangent measurements to the interface and properties of the deposited dielectrics, rather than to optimize the quality factor. In this configuration, thermally evaporated ≈1 µm thick amorphous germanium (a-Ge) films deposited on Si (100) have effective single-photon loss tangents of 4–5 × 10−6 and 9 μm-thick chemical vapor deposited homoepitaxial single-crystal Si has effective single-photon loss tangents of 4–14 × 10−6. Material characterization suggests that interface contamination could be the limiting factor for the loss.