Microwave Circuits Research Articles

Assessment of Measurement Uncertainty for S-Parameter Measurement Based on Covariance Matrix.

S-parameters are widely used to detail the scattering parameters of radio frequency (RF) components and microwave circuit modules. The vector network analyzer (VNA) is the most commonly used device for measuring S-parameters. Given the multiple frequency points, complex values, and intricate uncertainty propagation involved, accurately assessing the uncertainty of S-parameter measurements is difficult. In this study, we proposed a new method for assessing S-parameter uncertainty based on the covariance matrices, tracing back to the nominal uncertainty of calibration standards. First, we analyzed the relevant theory of uncertainty assessment using covariance matrices and subsequently deduced the mechanism of Type B uncertainty propagating from calibration standards to error model coefficients and S-parameter measurements to evaluate Type B measurement uncertainty. In this study, a novel measurement system was constructed for measuring grounded coplanar waveguides by using a VNA and calibration standards with 8- and 12-error models. Initially, the model assessed the Type B uncertainty of measuring four S-parameters of a grounded coplanar waveguide. Next, the VNA calibrated with the 12-error model was used to conduct multiple repeated measurements to assess the Type A uncertainty of the grounded coplanar waveguide. Finally, the composite uncertainty was constructed, which demonstrated that the proposed method can be used for assessing the uncertainty of S-parameters.

Recent development in reconfigurable dielectric resonator antenna and microwave filter: design and application

SummaryDeveloping wireless communication systems depends on reconfigurable microwave filters (MF) and dielectric resonator antenna (DRA) because the functionality of the various filters and antennas available for a wireless communication system is limited, and reconfigurable DRA and MF are utilized to overcome these limitations. The throughput of a multiantenna system can be achieved with reconfigurable DRA and filter. Various switching strategies and classifications of reconfigurable DRA and MF are presented. The electrical reconfiguration technique is most suitable for developing a reconfigurable DRA and filter among all the switching techniques. In this approach, reconfigurability may be accomplished by utilizing a PIN diode, a varactor diode, and a radio‐frequency microelectromechanical switch (RF‐MEMS). These switches are more reliable, highly efficient, and easily integrated with the microwave circuit. Reconfigurable DRA with machine learning is demonstrated. The application of reconfigurable DRA and filters in cognitive radio (CR) is also demonstrated. Also, the review article focused on the performance parameters, design, and challenges of reconfigurable antenna and MF.

3-D Printed Vertically Integrated Composite Right/Left-Handed Transmission Line and Its Applications to Microwave Circuits

3-D Printed Vertically Integrated Composite Right/Left-Handed Transmission Line and Its Applications to Microwave Circuits

Electro-optomechanical entanglement in two coupled optical cavities with an LC microwave circuit

We theoretically investigate entanglement in a hybrid quantum system comprising two optical cavities coupled to a shared microwave cavity via optomechanical interactions. Our results demonstrate that increasing the microwave input power and frequency in the allowed range enhances entanglement between the microwave–optical and optical–optical modes. We also show by change frequency of the one optical cavity in the communication domain that we still have entanglement. This ability to generate robust microwave–optical photon entanglement shows promise for various quantum technologies. Optical photons could enable secure quantum communication in optical fibers, while microwave photons allow transmission to satellites. Overall, this hybrid cavity optomechanical system offers prospects as an efficient source of entangled photon pairs, vital for implementing long-distance quantum communication networks.

Optimizing MMIC performance: The synergy of AI models and heterogeneous integration process

AbstractThis study presents a novel approach for optimizing the parameters of monolithic microwave integrated circuit (MMIC) functional units using machine‐learning techniques and multi‐objective optimization algorithms. We utilize advanced machine‐learning methods, including random forest, artificial neural networks (ANNs), and recurrent neural networks (RNNs), to construct highly accurate models that predict the performance of these units. These models are subsequently integrated with a multi‐objective optimization algorithm, specifically the multi‐objective particle swarm optimization (MOPSO), to generate inverse design solutions for both the geometric designs of the units and the fabrication parameters of the heterogeneous integration process. Our approach, which has been validated through chip fabrication and testing, has demonstrated its robustness as a tool for achieving optimal MMIC designs. It not only reduces the design time but also enhances the manufacturability of MMICs, thereby opening new avenues in microwave and RF circuit design.

Study on reliability of gold belt welding for Aerospace Microwave Circuit

As a highly reliable and flexible interconnection method, gold belt welding is widely used in the interconnection of aerospace microwave circuits. In this paper, to reveal the influence of the technological parameters of gold belt welding on stress, the typical aerospace electronic equipment was studied by Ansys finite element software. The result shows that the stiffness consistency of two structures which are connected by a gold belt and the winding radius of the gold belt are the crucial factors in the reliability of gold belt connection. A process-strengthening measure has been proposed based on the analysis results. The verification of the process experiment shows that using EC2216 adhesive on both sides of a gold belt can effectively reduce stress and improve mechanical reliability. Furthermore, the analytical methods and measures have been extended to other flexible interconnection methods, which provide a solution to the highly reliable interconnection in the aerospace product.

Coplanar Waveguide (CPW) Loaded with Symmetric Circular and Polygonal Split-Ring Resonator (SRR) Shapes

This paper investigates the performance of coplanar waveguide (CPW) structures loaded with symmetric circular and polygonal split-ring resonators (SRRs) for microwave and RF applications, leveraging their unique electromagnetic properties. These properties make them suitable for metamaterials, sensors, filters, resonators, antennas, and communication systems. The objectives of this study are to analyze the impact of different SRR shapes on the transmission characteristics of CPWs and to explore their potential for realizing compact and efficient microwave components. The CPW-SRR structures are fabricated on a dielectric substrate, and their transmission properties and spectrogram are experimentally characterized in the frequency range of 4 GHz to 10 GHz with the rotation angles of the SRR gap. The simulation results demonstrate that the resonant frequencies and magnitude of the transmission coefficient of the CPW-SRR structures are influenced by the geometry of the SRR shapes and the rotation angles of the SRR gap, with certain shapes exhibiting enhanced performance characteristics compared to others. Moreover, the symmetric circular and polygonal SRRs offer design flexibility and enable the realization of miniaturized microwave components with improved performance metrics. Overall, this study provides valuable insights into the design and optimization of CPW-based microwave circuits utilizing symmetric SRR shapes, paving the way for advancements in the miniaturization and integration of RF systems.

Expedited re-design of multi-band passive microwave circuits using orthogonal scaling directions and gradient-based tuning

Geometry scaling of microwave circuits is an essential but challenging task. In particular, the employment of a given passive structure in a different application area often requires re-adjustment of the operating frequencies/bands while maintaining top performance. Achieving this necessitates the utilization of numerical optimization methods. Nonetheless, if the intended frequencies are distant from the ones at the starting point, local search procedures tend to fail, whereas global search algorithms are computationally expensive. As recently demonstrated, a combination of large-scale concurrent geometry parameter scaling with intermittent local tuning allows for dependable re-design of high-frequency circuits at low CPU costs. Unfortunately, the procedure is only applicable to single-band structures due to synchronized modifications of all operating bands under scaling. This article discusses a novel procedure that leverages a similar overall concept, but allows for independent control of all center frequencies. To achieve this goal, an automated decision-making procedure is developed in which a set of orthogonal scaling directions are determined based on their effect on individual circuit bands, and using auxiliary optimization sub-problems. The scaling range is then automatically computed by solving an appropriately-defined least-square design relocation problem. The methodology introduced in the work is illustrated using two planar passive devices. In both cases, wide-range operating frequency re-design has been demonstrated and favorably compared to conventional gradient-based tuning. Furthermore, the presented procedure has been shown to be computationally efficient. It is also easy to implement and integrate with a variety of gradient-based optimization procedures of a descent type.

Research and Design of the RF Cavity for an 11 MeV Superconducting Cyclotron

In contrast to the room temperature cyclotron, the superconducting cyclotron’s high operational magnetic field and small extraction radius lead to a magnet design with a reduced radius. This limits the space available for the RF cavity in the 11 MeV superconducting cyclotron, necessitating a more compact RF cavity design. By using the transmission line theory, the complex structure of the quarter-wavelength coaxial cavity can be represented as a microwave circuit. Through relevant theoretical analytical formulas, equivalent circuit parameters can be derived. The resonant frequency of the RF cavity is then determined using the equivalent circuit method. The optimization of the RF cavity structure was achieved by creating a numerical model and conducting finite element numerical calculations on the high-frequency resonant system. The comparative results between the equivalent circuit and numerical calculations indicate that the frequency error remains within 0.1%, validating the compact RF cavity design. A multiple linear regression analysis facilitates the prediction of resonance frequency across various parameter variables. By analyzing the fitting formula, RF cavity machining error requirements are established, ensuring a prediction error within 1%, thus meeting engineering design criteria.

A compact Non-Quasi-Static small-signal model for GaN HEMT

In this work, we introduce a compact Non-Quasi-Static (NQS) model for the long-channel Gallium nitride high-mobility field effect transistor based on charge-based EPFL (École Polytechnique fédérale de Lausanne) HEMT model implemented in Verilog-AMS modeling language. The proposed model has been validated for the low-frequency (quasi-static) operating region as well as high frequencies up to sub-terahertz. This model has been derived from the analytical solution of the drift–diffusion and continuity equations based on physically valid assumptions. Polynomial approximation was used to make the model design-oriented and compatible with conventional circuit simulators for designing microwave circuits. Intrinsic trans-admittance parameters, obtained from the model for two devices with channel lengths of 1μm and 10μm has been validated with TCAD simulation results. Besides, the scattering parameters for the GaN HEMT equivalent circuit, have been validated with TCAD simulations and with our previous work, which already validated with experimental data. These results confirm the effectiveness of the proposed compact model for circuit simulations.

A simple 90° hybrid branchline coupler with wideband phase balance for 5G applications

Abstract A 90° hybrid coupler operating at a central frequency of 5.40 GHz is introduced, offering high-performance characteristics with compact dimensions of 616.65 mm² (33.3 mm × 18.5 mm). These features are achieved while maintaining a design that makes it easy to produce. The unique aspect of this microstrip FR4 substrate-based design is the consistent S-parameters, which remain steady despite changes in structural dimensions, thereby making it adaptable to fabrication variations. The reported S-parameters measured in 5.4 GHz are as follows: |S11|= –29.46 dB, |S21|= –4.11 dB, |S31|= –3.96 dB, and |S41|= –21.23 dB. This hybrid coupler operates over a bandwidth of 0.8 GHz (16%), demonstrating remarkable performance within this spectrum. In addition to its design, the coupler exhibits robust resilience against changes in substrate parameters and structural dimensions, ensuring reliability during the fabrication process. Following thorough simulation studies, a physical prototype of the coupler was constructed and subjected to laboratory measurements. The experimental results align closely with the simulation data, validating the accuracy and predictability of the design. In comparison with other studies and designs documented in the literature, this compact, high-performance 90° hybrid coupler exhibits clear advantages in terms of size, isolation, phase deviation, and structural complexity. Therefore, the benefits and applicability of this presented structure in the context of microwave circuits and systems are underscored. It’s noteworthy to mention that the central frequency of 5.4 GHz falls within the sub-6 GHz 5G band range.

Butyl rubber dispersed with low-loss Ca0.61Nd0.26TiO3 ceramics for miniaturized flexible microwave substrate applications

Ca0.61Nd0.26TiO3 (CNT)-filled butyl rubber (BR) composites were fabricated via Banbury mixing by changing the ceramic volume fraction from 0 to 0.5. The phase purity of the CNT filler was confirmed using X-ray diffraction, and the morphology of the composite samples was analyzed using scanning electron microscopy and atomic force microscopy. BR/CNT composites filled with 50 vol% filler possessed excellent dielectric properties with a dielectric constant of 11.12 and a very low dielectric loss of 0.0023 in the X-band (8–12 GHz) frequencies. Moreover, the material displayed an appreciable thermal conductivity of 0.883 W/mK, low water absorption of 0.0574 %, and an acceptable CTE of 37.08 ppm/ °C. Thus, the developed BR/CNT composites can be used for flexible microwave circuit applications that require miniaturization.

Universal control of a bosonic mode via drive-activated native cubic interactions

Linear bosonic modes offer a hardware-efficient alternative for quantum information processing but require access to some nonlinearity for universal control. The lack of nonlinearity in photonics has led to encoded measurement-based quantum computing, which relies on linear operations but requires access to resourceful (’nonlinear’) quantum states, such as cubic phase states. In contrast, superconducting microwave circuits offer engineerable nonlinearities but suffer from static Kerr nonlinearity. Here, we demonstrate universal control of a bosonic mode composed of a superconducting nonlinear asymmetric inductive element (SNAIL) resonator, enabled by native nonlinearities in the SNAIL element. We suppress static nonlinearities by operating the SNAIL in the vicinity of its Kerr-free point and dynamically activate nonlinearities up to third order by fast flux pulses. We experimentally realize a universal set of generalized squeezing operations, as well as the cubic phase gate, and exploit them to deterministically prepare a cubic phase state in 60 ns. Our results initiate the experimental field of polynomial quantum computing, in the continuous-variables notion originally introduced by Lloyd and Braunstein.

Violation of detailed balance in microwave circuits: theory and experiment

We propose an approach to detailed balance violation in electrical circuits based on the scattering matrix formalism commonly used in microwave electronics. This allows us to easily include retardation effects, which are paramount at high frequencies. We define the spectral densities of phase space angular momentum, heat transfer and cross power, which can serve as criteria for detailed balance violation. We confirm our theory with measurements in the 4–8 GHz frequency range on several two port circuits of varying symmetries, in space and time. This validates our approach, which enables straightforward treatment of quantum circuits at ultra-low temperature.

Non-Linear Simulation by Harmonic Balance Techniques of Load Modulated Power Amplifier Driven by Random Modulated Signals

The simulation of the steady state and the non-linear stability of a load modulated power amplifier (LMPA) driven by a random modulated generator, fully performed in the frequency domain by harmonic balance (HB) techniques, is presented. The non-linear microwave circuit and the driving pseudo-random modulated (PRM) generator are integrally defined in the frequency domain. The simulation is implemented and performed using commercially available circuit simulation software. The demodulation of the output signal of the LMPA is implemented with optimally matched filters as software-defined demodulation. The simulated dynamic results of a Quasi-MMIC GaN Doherty power amplifier (DPA) are shown and compared to the measured results with a 16-QAM driving signal at 10 MS/s. The time-domain measurement allows the validation of the new simulation technique through the comparison of both the measured and the simulated error vector magnitude (EVM), the left and right adjacent channel power ratios (ACPRs) versus the average output power. This new simulation is then called pseudo-random modulated harmonic balance (PRM-HB) simulation. The full PRM-HB simulation of an LMPA driven by a random modulated signal, performed in the frequency domain at the design circuit level, results in an advanced simulation tool in the frame of the design of RF circuits and subsystems for telecommunication applications.

Electric near-field scanning for electronic PCB electromagnetic radiation measurement

This paper introduces a design and test of an electric (E) near-field scanning (NFS) system by using innovative 4-layer miniature probe for electromagnetic compatibility (EMC) application. The probe works in the challenging frequency band up to 12 GHz with spatial resolution lower than 2 mm. The NFS is designed to operate by automation based on PC driven by LabVIEW® interface controlling a vector network analyzer (VNA). The PC communicates with the VNA through the local area network to read and save the measured data emitted by the device under test (DUT). The LabVIEW® interface is designed to control the E-NF positioning motion core by means of STM32® microcontroller. A stepper motor is used to move the E-NF probe along the scanning surface plan. Finally, the NFS is validated by visualizing the E-NF intensity maps generated in real time after calibration with a reference device under test represented by microstrip line and a microwave circuit.

Electronic, Elastic, Optical, and Thermodynamic Properties Study of Ytterbium Chalcogenides Using Density Functional Theory

In this study, the structural, electronic, optical, elastic, and thermodynamic properties of Ytterbium chalcogenides YbX (X = S, Se and Te) were computed within the first principles using generalized gradient approximation (GGA) as implemented in the pseudopotential plane wave approach. The equilibrium total energy for YbX (X = S, Se, and Te) was calculated as a function of the energy cutoff, k-point grid, and lattice parameter. An optimized lattice parameter of 5.6, 5.66, and 6.136 Å were calculated for YbS, YbSe, and YbTe, respectively. The energy band gaps of YbS, YbSe, and YbTe computed are 1.14, 1.32, and 1.48 eV, respectively. In addition, the low band gap (less than 3 eV) for ytterbium chalcogenides indicated that they may have potential applications in photovoltaic cells and laser diodes. Moreover, the negative dielectric function value for a certain frequency range indicates that these compounds are suitable for specific optical and microwave circuit applications. The result of elastic and thermodynamic property computation reveals that ytterbium chalcogenides are mechanically and thermodynamically stable, which can be useful in a variety of electronic device applications.

An intelligent digital twinning approach for complex circuits

The digital twinning process is essential for transferring real-world objects to the Metaverse by creating accurate digital versions, known as digital twins. However, complex systems pose challenges in this process. With the increasing utilization of microwave components and circuits in telecommunication systems such as IoT, 5 G, and 6 G, the need for digital twins of these components arises. Nevertheless, high-frequency components exhibit intricate behavior, requiring advanced modeling techniques. Artificial intelligence (AI) provides a powerful tool for enhancing the reliability and accuracy of estimated models in such cases. In this study, a microstrip lowpass filter (LPF) is designed, fabricated, and measured as the physical twin. An intelligent digital twinning approach is employed using a machine learning method based on an adaptive neuro-fuzzy inference system (ANFIS), trained by a subtractive clustering algorithm. The resulting digital twin of the LPF proves valuable for communication networks and IoT applications. Moreover, this research showcases the applicability and accessibility of machine learning in creating digital twins of electromagnetic components for communication cyber-physical systems (CPSs) and the Metaverse. Furthermore, the proposed method exhibits adaptability to various passive and active electrical or electronic circuits. By harnessing the potential of AI and digital twinning, this study presents a robust and accurate approach for modeling and analyzing complex circuits, specifically in the context of communication systems and their integration into the Metaverse. The findings highlight the advantages of an intelligent digital twinning approach and its potential for advancing various domains involving complex circuitry.

A New Compact Wideband Filter Based on a Coupled Stepped Impedance Resonator.

A new compact wideband filter is introduced to address the requirements of recent communication and radar systems. The filter is based on a quarter-wavelength short-circuit coupled stepped impedance resonator (SIR). The analytical solution shows that the suggested SIR resonator provides a compact size and a wide stopband response, which are essential features in many wireless communication systems. The analytical results also reveal that increasing the impedance ratio of the SIR extends the stopband by increasing the first spurious response and reducing its total length. A compact two-coupled short-circuit SIR filter is designed at 1.23 GHz. The design approach is validated using an ideal transmission line modeling analysis and electromagnetic simulation using CST Microwave Studio 2021. The proposed structure is shown to be flexible, allowing the achievement of a relative bandwidth as low as 5% and as high as 50%. A four-resonator filter is designed by cascading two stages of the designed two-coupled short-circuit SIR filter, which are coupled through a quarter-wavelength line. The simulation results illustrate that the suggested structure can be used to design a filter with any number of resonators. The filter is implemented using a high-resolution LPKF laser machine on Rogers RT/duroid 6010.2LM material with a thickness of 0.635 mm. From the measurements, the bandwidth is found to be 390 MHz and centered at 1325 MHz (29.4% relative bandwidth) and the insertion loss is 1.3 dB. The simulation and experimental results verify the proposed approach and indicate the potential of this component in meeting the design requirements of next-generation microwave circuits related to flexibility and size-compactness.

Development of a New Equivalent Circuit of DGS with Ideal Transformer

In this paper, a new equivalent circuit of a rectangular dumbbell‐shaped defected ground structure (DGS) with an ideal transformer is proposed. The proposed circuit incorporates a parallel resistor in the DGS gap, enabling the extraction of the coupling coefficient of DGS occurring in the narrow line gaps. Both circuit simulations and measurements demonstrate excellent agreement, confirming excellent performance compared to the measured results. Unlike the conventional equivalent circuit, which consists only of the lumped element, this one has an accuracy of only DGS units. In the proposed circuit, an ideal transformer has higher accuracy for the DGS in parallel with a resistor. We observed that increasing the resistance of the parallel resistor on the DGS unit leads to a decrease in the coupling coefficient and, conversely, decreasing the resistance prompts an increase in the coupling coefficient. The goal of this study is to develop a new equivalent circuit for a DGS unit with the ideal transformer, especially to find the coupling coefficient that occurred in the DGS gap. Here, we analyzed that the structure of the DGS unit had a gap, and the coupling coefficient must be built into any value. To demonstrate the effectiveness of the proposed circuit, DGS was used to design and conduct fabrication and measurement. The advantages of the proposed circuit analysis of the DGS behavior can be used to develop the attenuation pole as a one‐pole low‐pass filter, paving the way for future applications and developments in microwave and RF circuit design.