Microwave Circuit Simulation Research Articles

GPS위성 RF신호수신 이중대역 소형 하이브리드 결합기의 회로모델링과 설계

This paper presents a compact branch-line coupler working for receiving GPS signals at two adjacent frequencies as one geometry. The GPS receiver must have the feed circuit handling a circularly polarized electric field entering the radiating element leading up to division into quadrature branches, which has been used in the conventional works. But, it takes one frequency and a new approach is needed to take two frequencies. A lattice comprising segments loaded with series and parallel capacitors and circumferential inductors is built to make the branch-line coupler handle two frequencies. L1 and L2 bands for GPS are chosen and the circuit modelling is conducted to design the component. The method is verified by running a microwave circuit simulator and measurement of the s-parameters of the fabricated prototype. The power division and reflection coefficient at 1.5 GHz as L1- and 1.2 GHz as L2-band show the result is in good agreement with the required performance.

Deep Neural Networks for Rapid Simulation of Planar Microwave Circuits Based on Their Layouts

This article demonstrates a deep learning (DL)-based methodology for the rapid simulation of planar microwave circuits based on their layouts. We train convolutional neural networks (CNNs) to compute the scattering parameters of general, two-port circuits consisting of a metallization layer printed on a grounded dielectric substrate, by processing the metallization pattern along with the thickness and dielectric permittivity of the substrate. This approach harnesses the efficiency of CNNs with pattern recognition tasks and extends previous efforts to employ neural networks for the simulation of parameterized circuit geometries. Furthermore, we integrate this CNN in a hybrid network with a long-short term memory (LSTM) module that uses coarse mesh finite-difference time-domain (FDTD) simulation data as an additional input. We show that this hybrid network is computationally efficient and generalizable, accurately modeling geometries well beyond those that the network has previously seen.

A-EFIE With Model-Order Reduction Technique for Fast Analysis of Circuit Simulation

A fast frequency-sweep method for microwave circuit simulation based on a full-wave solver is presented in this letter. The complexity of the mathematical model of the augmented electric field integral equation (A-EFIE) system is reduced by employing the model-order reduction (MOR) technique, where the reduced-order subspace is constructed by singular value decomposition (SVD). Compared to the A-EFIE with the asymptotic waveform evaluation (AWE) technique, the A-EIFE with the SVD-based MOR technique can speed up the broadband circuit analysis more efficiently.

Simulation and Automated Modeling of Microwave Circuits: State-of-the-Art and Emerging Trends

Microwave modeling and simulation are essential to designing microwave circuits and systems. Although fundamental concepts and approaches for modeling and simulation are mature, the drive to higher frequencies, tighter design margins, and more functionality/complexity of circuits continue to defy the capabilities of existing modeling and simulation methods. Newer algorithms are being developed to address the speed, accuracy and robustness of design algorithms. Coupled with the advent of more powerful computers and algorithms, microwave design automations are solving much more complex problems in much shorter time than previously imaginable. This paper describes the advances and state-of-the-art in automated modeling and simulation. Automated data-driven modeling approaches covering data sampling/generation, model structure adaptation, and model training/validation are described. Simulation of nonlinear microwave circuits is described covering formulations of simulation equations and advanced solution algorithms addressing problem size, convergence speed and solution accuracy. The descriptions highlight fundamental concepts, advanced methodologies, and future trends of development.

Non-quasi-static Effects Simulation of Microwave Circuits based on Physical Model of Semiconductor Devices

This work explores analyzing the non-quasistatic effects of a microwave circuit by employing a physical model-based field-circuit co-simulation method. Specifically, it uses the semiconductor physical model to characterize the semiconductor devices, and simulates the lumped circuit by cooperating semiconductor physical equations into Kirchhoff’s circuit equations. Then the lumped circuit simulation is hybridized with the finite-difference time-domain (FDTD) simulation by interfacing EM (electromagnetic) field quantities with lumped-element quantities at each timestep. Taken a microwave limiter circuit as an example, the simulation results agree well with the measured results, which prove that this method can characterize non-quasi-static effects well. As a comparison, the equivalent circuit modelbased co-simulation cannot characterize the non-quasistatic effects accurately.

Compact wideband circularly‐polarized antenna for universal UHF RFID handheld reader

AbstractA compact wideband circularly‐polarized (CP) RF identification (RFID) handheld reader antenna based on inverted‐F antennas (IFAs) is proposed. The antenna consists of an upper layer of rotationally symmetric radiation structure and lower layer of feed network. Firstly, the feed network is verified by microwave circuit simulation software. Then the antenna is modeled and simulated with the aid of the full‐wave electromagnetic simulation software. Finally, a prototype is fabricated using FR4 plate and its performance of the proposed antenna is validated. The measured impedance bandwidth of 10 dB and the axial ratio (AR) bandwidth of 3 dB are wider than 13%. The peak gain is greater than 2.2 dBic, and the minimum AR is less than 1.1 dB, with the symmetrical and stable radiation patterns. The antenna has the compact size of 60 × 60 × 15 mm3. The proposed antenna can not only meet the requirements of RFID handheld reader applications in universal ultra‐high frequency (UHF) band (840‐960 MHz), but also has the advantages of wideband, small size, lightweight, low cost, and simple structure. Therefore, the design has a good application prospect in the field of Internet of Things.

Comparison of memristor models for microwave circuit simulations in time and frequency domain

As reported in the open literature, there are many memristor models for the circuit-level simulations. Some of them are not particularly suitable for microwave circuit simulations. At RF/microwave frequencies, the memristor dynamics become an important issue for the transition process. In this paper we present a number of different SPICE memristor model groups. Each group is explained using representative models, which are analysed and compared from the microwave circuit analysis viewpoint. We consider the model behaviour at RF/microwave frequencies and the memristance setting issues. Results are compared and the best models are recommended.

Impact of the Characteristic Impedance of Coaxial Lines on the Sensitivity of a 750-MHz Electronically Tunable EPR Resonator

A 750-MHz electronically tunable resonator was investigated in terms of the sensitivity of electron paramagnetic resonance (EPR) signal detection. The conversion efficiency of the radio-frequency magnetic field was calculated for resonators with 50- and 100-Ω coaxial coupling lines using three-dimensional (3D) microwave field and microwave circuit simulators. Based on the simulation results, two tunable resonators were physically constructed and compared in terms of EPR signal sensitivity using a nitroxyl radical solution. While the resonator with 100-Ω coaxial lines provided 14% greater signal intensity, its signal-to-noise ratio was lower than that of the resonator with 50-Ω lines. To demonstrate the capability of the constructed tunable resonator for EPR imaging experiments, a solution of nitroxyl radical and the leg of a tumor-bearing mouse were visualized.

Cylindrical to rectangular coordinate transformation for planar phase front synthesis

Coordinate transformation technique is employed to engineer a metamaterial slab that enables planar wave emission from a planar or line localised source. First a rigorous cylindrical to rectangular coordinate transformation is applied resulting in with a sheet current generating a plane wave with impedance matching at the boundary between the device and the surrounding medium. Then, based on physical reasoning, the material constitutive parameters are further reduced to having only one entry of the spatially varying permeability tensor instead of two entries as discussed in the references. This further reduction is equivalent to modifying the near field in the transformed domain. Finally, due to a specific mu-near-zero condition near the origin, the sheet source is transformed to a localised one in the transformed domain and via full-wave simulations, the authors show that the field is still propagating as a plane wave. Moreover, the transmission line (TL) metamaterial implementation with discretised spatially varying permeability is designed. The capacitor- and inductor-loaded two-dimensional TL grid is used to synthesise the required spatially varying relative permeability in the wavefront converter metamaterial slab. The TL metamaterial design is proven to successfully synthesise a planar wave front using a microwave circuit simulator.

Overcoming the Realization Problems of Wideband Matching Circuits

During the analytical design process of wideband impedance matching major problems may arise, that might lead to non-realizable matching networks, preventing the successful impedance matching. In this paper two practical design rules and a simplified equation is presented, supporting the design of physically realizable impedance matching networks. The design rules and calculation technique introduced by this paper is summarized, and validated by microwave circuit simulation examples.

COMPARATIVE ANALYSIS OF DIFFERENT CAD METHODS FOR EXTRACTION OF THE HEMT NOISE WAVE MODEL PARAMETERS

The noise wave model has appeared as a very appropriate model for the purpose of transistor noise modeling at microwave frequencies. The transistor noise wave model parameters are usually extracted from the measured transistor noise parameters by using time-consuming optimization procedures in microwave circuit simulators. Therefore, three different Computer-Aided Design methods that enable more efficient automatic determination of these parameters in the case of high electron-mobility transistors were developed. All of these extraction methods are based on different noise de-embedding procedures, which are described in detail within this paper. In order to validate the presented extraction methods, they were applied for the noise modeling of a specific GaAs high electron-mobility transistor. Finally, the obtained results were used for the comparative analysis of the presented extraction approaches in terms of accuracy, complexity and effectiveness.

A 750-MHz Electronically Tunable Resonator Using Microstrip Line Couplers for Electron Paramagnetic Resonance Imaging of a Mouse Tumor-Bearing Leg.

The purpose of this work was to develop an electronically tunable resonator operating at 750 MHz for continuous-wave electron paramagnetic resonance (CW-EPR) imaging of a mouse tumor-bearing leg. The resonator had a multi-coil parallel-gap structure with a sample space of 16 mm in diameter and 20 mm in length. Microstrip line couplers were used in conjunction with varactor diodes to enable resonance frequency adjustment and to reduce the nonlinear effects of the varactor diodes. The resonator was modeled by the finite-element method and a microwave circuit simulation was performed to clarify its radiofrequency characteristics. A tunable resonator was evaluated in terms of its resonance frequency, tunable frequency band, and conversion efficiency of the RF magnetic field. The developed resonator provided a tunable frequency band of 4 MHz at a central frequency of 747 MHz and a conversion efficiency of 34 μT/W1/2. To demonstrate the application of this tunable resonator to EPR imaging, three-dimensional EPR images of a sample solution and a mouse tumor-bearing leg were obtained. The developed tunable resonator satisfied our initial requirements for in vivo EPR imaging and may be able to be further improved using the present finite-element and circuit models if any problems arise during future practical applications. This work may help to promote EPR imaging of tumor-bearing mice in cancer-related studies.

A symmetric coupled line equivalent circuit model for asymmetric coupled lines

A new equivalent circuit model is proposed for an asymmetric coupled line based on a symmetric coupled line. The proposed equivalent circuit consists of a symmetric coupled line and two ideal transformers to represent an asymmetric coupled line and can be easily incorporated into the existing microwave and RF circuit simulators. This makes it easier to model and simulate the asymmetric coupled line circuits in terms of simple symmetric coupled lines. Using the proposed equivalent circuit model, it is shown that an asymmetric coupled line coupler is electrically equivalent to a symmetric coupled line coupler with transformed port impedances and the relation between the two couplers is investigated through the established equivalence. The validity of the proposed model is confirmed through the analysis of the directional couplers and the impedance transformers involving the asymmetric coupled lines. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:277–282, 2016.

Wave propagation in two‐dimensional left‐handed non‐linear transmission line metamaterials

Recent research on harmonic generations in one-dimensional (1D) left-handed non-linear transmission line (LH NLTL) metamaterials has shown that the fundamental wave and its higher harmonics can realise quasi-phase matching, which in turn ensures the high conversion efficiency of the harmonics. In this study, the authors first present the electromagnetic (EM) theory to describe the generation and propagation of both second-harmonic (SH) and third-harmonic (TH) waves in a 2D non-linear transmission line metamaterial. Then, with the aid of the microwave circuit simulations, they fabricate a 2D LH NLTL metamaterial and demonstrate that an EM wave propagation in such medium has three states: left-handed (LH), right-handed (RH), and non-propagation. Furthermore, the response of the medium to applied field intensity shows that it can realise self-tuning between LH and RH states for the TH waves.

Modeling of a Planar Metamaterial Power Divider/Combiner Using Transmission Matrix Method

This letter presents a circuit modeling approach to analyze the scattering parameter and spatial voltage distribution of a planar nine-way metamaterial power-divider/combiner structure. The analysis is based on the multi-input and multi-output transmission matrix method. Computation results of this nine-way metamaterial power divider/combiner are shown in good agreement with simulation results using commercial microwave circuit simulator and measurement results.

DESIGN OF A 90° SWITCHED LINE PHASE SHIFTER FOR PHASED ARRAY ANTENNAS

Phase shifters are considered as the most vital subsystem for an antenna in any transceivers or RADARs. As the name suggests that, these components provide phase shift for the input signal, with respect to the reference signal at its output without any loss or modifications in the amplitude of input. In this work, an attempt has been made to design a 90⁰ phase shifter based on switched line type. The phase shifter is designed to implement on a microstrip circuit type. The frequency considered for the operation is 1 GHz. Agilent’s ADS (Advanced Design Simulation) software tool was used for designing and simulating the switched line phase shifter. The ADS software is widely used for designing and the simulation of microwave circuits and its components. Initially the circuit was designed with ideal switch models, which are readily available in ADS. Then independent single pole double throw switches were designed and simulated again. Parameters like return loss and insertion loss were considered as main parameters and then the designs were optimized to achieve the best possible return loss and insertion loss.

Modeling and Simulation of Microwave Circuits

A new and efficient method is presented for the analysis of arbitrarily shaped discontinuities. The technique obtains closed form expressions for the equivalent circuits which are used to model these discontinuities. Then it would be easy to handle and to characterize complicated structures like T and Y junctions, truncated junctions, arbitrarily shaped junctions, cascading junctions and more generally planar multiport junctions. Another advantage of this method is that the edge line concept for arbitrary shape junctions operates with real parameters circuits. The validity of the method was further confirmed by comparing our results for various discontinuities (bend, filters) with those from HFSS as well as from other published sources.

Analog study of near-field focusing and subwavelength imaging with nonlinear transmission-line metamaterial

In this paper, we report an analog study of realizing near-field focusing and near-perfect imaging at harmonic frequencies using a two-dimensional (2D) left-handed nonlinear transmission line (LH NLTL) metamaterial. Firstly, we give a detailed procedure of designing LH NLTL and right-handed (RH) transmission line media that match with each other at harmonics. Then, through microwave circuit simulations, we observe strong surface waves at the boundaries between RH and LH NLTL metamaterials, which are consistent with the theoretical analysis of an LH linear superlens. Finally, we show that the LH NLTL metamaterial can act as a flat nonlinear lens that can create, with a subwavelength resolution, an image of harmonic fields of the source which is opaque at the fundamental frequency.

Time‐domain techniques in microwave circuit simulation

Microwave circuit simulation has always posed particular difficulties especially in highly non-linear applications because of the presence of distributed or electromagnetic structures, which are usually passive and linear, but difficult to incorporate effectively in time-domain analysis. A variety of specialised techniques has evolved to cope with this situation with reasonable success. In recent years, microwave systems are becoming more integrated and complex and often involve `mixed-signals' that may operate over a very wide range of time scales, creating new simulation challenges. This study reviews the issues involved and suggests a practical paradigm for generalised time-domain simulation of microwave circuits.

An extraction technique for small signal intrinsic parameters of HEMTs based on artificial neural networks

This paper presents a fast and accurate procedure for extraction of small signal intrinsic parameters of AlGaAs/GaAs high electron mobility transistors (HEMTs) using artificial neural network (ANN) techniques. The extraction procedure has been done in a wide range of frequencies and biases at various temperatures. Intrinsic parameters of HEMT are acquired using its values of common-source S-parameters. Two different ANN structures have been constructed in this work to extract the parameters, multi layer perceptron (MLP) and radial basis function (RBF) neural networks. These two kinds of ANNs are compared to each other in terms of accuracy, speed and memory usage. To validate the capability of the proposed method in small signal modeling of GaAs HEMTs, data and modeled values of S-parameters of a 200μm gate width 0.25μm GaAs HEMT are compared to each other and very good agreement between them is achieved up to 30GHz. The effect of bias, temperature and frequency conditions on the extracted parameters of HEMT has been investigated, and the obtained results match the theoretical expectations. The proposed model can be inserted to computer-aided design (CAD) tools in order to have an accurate and fast design, simulation and optimization of microwave circuits including GaAs HEMTs.