Introductory review on object oriented paradigm for full‐wave microwave CAD

Object oriented (OO) techniques are proving useful in software engineering for dealing with complex systems and for increasing the ease of code development and maintainability. However, their application to electromagnetic modeling is still in its infancy. A brief introduction for microwave engineers to OO paradigms is made. A review of the state of the art in OO full‐wave electromagnetic modeling is made, an illustrative example is shown, and likely future trends are discussed. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 341–353, 2002. Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mmce10031     

A method for stability analysis of small-signal microwave amplifiers

This paper presents a method for analyzing the stability of small-signal microwave amplifiers with any topology. This analysis is performed using the Nyquist criterion and allows detection of the so-called odd-mode instabilities. The method is easily applicable by using commercially available microwave CAD. © 1998 John Wiley & Sons, Inc. Int J RF and Microwave CAE 8: 293–302, 1998.     

Switched-mode RF and microwave parallel-circuit Class E power amplifiers

The parallel-circuit Class E tuned power amplifiers with load networks consisting of either one capacitance and one inductor or a parallel LC circuit and series filter are described and analyzed. The elements of the load networks are defined using the same analytical approach with a set of the exact design equations. The ideal collector voltage and current waveforms for both configurations demonstrate a possible 100% efficiency and do not overlap. RF and microwave applications are demonstrated based on the simulation and experimental results of low-voltage InGaP/GaAs HBT and high-voltage LDMOSFET power amplifiers. These switched-mode parallel-circuit Class E power amplifiers offer a new challenge for RF and microwave power amplification by providing high-efficiency operating conditions. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14, 21–35, 2004.     

An eclectic approach to design tunable amplifiers

Broadband amplifiers that can accommodate commercial communication standards such as GSM, UMTS, Wi‐Fi, and Wi‐Max are extremely important for radio equipment manufacturers. To achieve this coverage, the amplifier should provide high gain and efficiency over a band from 800 to 5200 MHz. Although there are transistor devices that have cut‐off frequencies well over these frequencies, amplifiers covering such a broad‐bandwidth are difficult to design due to the requirement of broadband matching networks. In this work, design of broadband tunable matching networks is investigated using Real Frequency Direct Computational Technique (RF‐DCT). In order to be able to work on sample structures, impedance transforming filters are chosen and a broadband tunable matching network has been designed. Implementation of tunable inductors is investigated and the performance of a tunable matching network using tunable inductors and capacitors is demonstrated. Eventually a broadband frequency tunable amplifier has been designed using the tunable inductor concept. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Efficient surface reconstruction method for distributed CAD

This paper describes a new fast Reverse Engineering (RE) method for creating a 3D computerized model from an unorganized cloud of points. The proposed method is derived directly from the problems and difficulties currently associated with remote design over the Internet, such as accuracy, transmission time and representation at different levels of abstraction. With the proposed method, 3D models suitable for distributed design systems can be reconstructed in real time. The mesh reconstruction approach is based on aggregating very large scale 3D scanned data into a Hierarchical Space Decomposition Model (HSDM), realized by the Octree data structure. Then, a Connectivity Graph (CG) is extracted and filled with facets. The HSDM can represent both the boundary surface and the interior volume of an object. Based on the proposed volumetric model, the surface reconstruction process becomes robust and stable with respect to sampling noise. Moreover, the data received from different surface/volume sampling devices can be handled naturally. The hierarchical structure of the proposed volumetric model enables data reduction, while preserving significant geometrical features and object topology. As a result, reconstruction and transmission over the network are efficient. Furthermore, the hierarchical representation provides a capability for extracting models at desired levels of detail, thus enabling designers to collaborate at any product development stage: draft or detailed design.     

Fuzzy neural‐based approaches for efficient RF/microwave transistor modeling

In today's RF and microwave circuits, there is an ever‐increasing demand for higher level of system integration that leads to massive computational tasks during simulation, optimization, and statistical analyses, requiring efficient modeling methods so that the whole process can be achieved reliably. Since active devices such as transistors are the core of modern RF/microwave systems, the way they are modeled in terms of accuracy and flexibility will critically influence the system design, and thus, the overall system performance. In this article, the authors present neural‐ and fuzzy neural‐based computer‐aided design techniques that can efficiently characterize and model RF/microwave transistors such as field‐effect transistors and heterojunction bipolar transistors. The proposed techniques based on multilayer perceptrons neural networks and c‐means clustering algorithms are demonstrated through examples. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

A new neural network technique for the design of multilayered microwave shielded bandpass filters

In this work, we propose a novel technique based on neural networks, for the design of microwave filters in shielded printed technology. The technique uses radial basis function neural networks to represent the non linear relations between the quality factors and coupling coefficients, with the geometrical dimensions of the resonators. The radial basis function neural networks are employed for the first time in the design task of shielded printed filters, and permit a fast and precise operation with only a limited set of training data. Thanks to a new cascade configuration, a set of two neural networks provide the dimensions of the complete filter in a fast and accurate way. To improve the calculation of the geometrical dimensions, the neural networks can take as inputs both electrical parameters and physical dimensions computed by other neural networks. The neural network technique is combined with gradient based optimization methods to further improve the response of the filters. Results are presented to demonstrate the usefulness of the proposed technique for the design of practical microwave printed coupled line and hairpin filters. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

A Krylov‐subspace technique for the simulation of integrated RF/microwave subsystems driven by digitally modulated carriers

This article introduces a new approach to the analysis of nonlinear RF/microwave systems or subsystems described at the circuit level and excited by sinusoidal carriers modulated by arbitrary baseband signals. The circuit is simulated by a sequence of harmonic‐balance analyses based on a Krylov‐subspace method driven by an inexact Newton loop, and suitably modified to account for coupling with a finite number of preceding time instants. The Jacobian matrix of the nonlinear solving system is computed by an exact algorithm, and its structure is shown to be very well suited for the application of Krylov‐subspace techniques such as the GMRES method. In this way, problems with many millions of nodal unknowns may be efficiently tackled at the workstation level. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 490–505, 1999.     

微波热疗中的温度测量技术

概述了微波场中的温度检测技术,指出了它们的优点和存在的不足,提出一种微波热疗中的温度测量技术,实际制作了改进型的热电偶,并对它的抗电磁波干扰性进行了试验和分析,试验结果表明:该改进措施有效、可行。     

Novel synthesis technique for microwave circuits based on inverse scattering: Efficient algorithm implementation and application

In this article, an efficient algorithm implementation is presented for the synthesis of microwave circuits with arbitrary frequency responses. A comprehensive theory development is included starting from the formalism of the coupled‐mode theory to obtain an exact series solution for the inverse scattering problem. A final algorithm in pseudocode is available in this article together with graphical diagrams to provide a straightforward implementation for the interested reader showing its feasibility for parallel computing. As an example, a design of a matched filter for broadband communications is presented along with the operational insight of the applied method, the influence of the auxiliary parameters, and the comparison between target frequency responses, simulations, and measurements. This application in microstrip technology is enclosed as an instance of the versatility of our synthesis technique and the accuracy of the presented algorithm. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

New behavioral‐level simulation technique for RF/microwave applications. Part I: Basic concepts

The quadrature modeling technique is nowadays widely used for the nonlinear simulation of RF/microwave communication circuits and systems at the behavioral (system) level. It allows one to simulate the circuit/system performance under real‐world conditions and signals (using several thousand sample frequencies) and to predict such parameters as adjacent channel power ratio, spectral regrowth, and error vector magnitude in a computationally efficient way. But it is a narrowband technique and, consequently, cannot predict harmonics of the carrier frequency and even‐order nonlinear products, to account for the circuit/system frequency response and the bias decoupling network effect. Here, we propose a new behavioral‐level simulation technique (instantaneous quadrature technique) that overcomes these drawbacks, and demonstrate its validity through measurements and harmonic balance simulation. The transformation of envelope transfer characteristics into instantaneous ones is also discussed in detail. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 221–237, 2000.     

New behavioral‐level simulation technique for RF/microwave applications. Part III: Advanced concepts

The quadrature modeling structure is widely accepted as an efficient tool for the nonlinear simulation of RF/microwave bandpass stages (power amplifiers, etc.) for wireless applications. The common belief is that this structure can be applied to model only bandpass memoryless nonlinearities (which, however, may exhibit amplitude‐to‐phase conversion). In two recent articles 1 , 2 ; the authors have extended the application of the quadrature modeling structure to modeling broadband nonlinearities, which makes possible to predict harmonics and even‐order nonlinearities, to take into account the frequency response, etc. This article completes the overview of the instantaneous quadrature technique. The authors discuss its application to modeling AM, FM and PM detectors, which are strongly nonlinear elements with large memory (both the strong nonlinearity and large memory effects are essential for the detector proper operation), thus removing the limitation of nonlinearity to be memoryless or quasimemoryless. The identification of nonlinear interference/distortion sources is of great relevance for a practical EMC/EMI design. In the second part of this article, we discuss the dichotomous identification method, which is much more computationally efficient than a simple single‐signal method, especially for a large number of input signals. Individual spectral components of a complex‐spectrum signal can also be considered as input signals and, hence, it is possible to identify the spectral components responsible for a particular nonlinear interference/distortion (say, for a particular intermodulation product). © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 206–216, 2002.     

Nonlinear modeling of class‐E microwave power amplifiers

Verification of the Materka–Kacprzak model suitable for highly saturated MESFET operation is presented. To examine the validity of the model, a broadband microwave class‐E power amplifier was designed and fabricated using a Siemens CLY5 MESFET transistor. A 200 MHz bandwidth (22%) from 0.82 to 1.02 GHz with a power‐added efficiency greater than 60% was measured at an input power level of 15 dBm with a constant output power of 24 dBm. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 93–103, 1999     

Knowledge-guided inference for voice-enabled CAD

Voice based human-computer interactions have raised much interest and found various applications. Some extant voice based interactions only support voice commands with fixed vocabularies or preset expressions. This paper is motivated to investigate an approach to implement a flexible voice-enabled CAD system, where users are no longer constrained by predefined commands. Designers can, to a much more flexible degree, communicate with CAD modelers using natural language conversations. To accomplish this, a knowledge-guided approach is proposed to infer the semantics of voice input. The semantic inference is formulated as a template matching problem, where the semantic units parsed from voice input are the “samples” to be inspected and the semantic units in the predefined library are the feature templates. The proposed behavioral glosses, together with CAD-specific synonyms, hyponyms and hypernyms are extensively used in the parsing of semantic units and the subsequent template matching. Using such sources of knowledge, all the semantically equivalent expressions can be mapped to the same command set, and the Voice-enabled Computer Aided Design (VeCAD) system is then capable of processing new expressions it has never encountered and inferring/understanding the semantics at runtime. Experiments show that this knowledge-guided approach is helpful to enhance the robustness of semantic inference and can effectively eliminate the chance of overestimations and underestimations in design intent interpretation.     

Effective linearization technique for amplifiers operating close to saturation

The linearization technique that uses simultaneous injection of the second harmonics into the amplifier input and their feedforwarding to the amplifier output is suggested. This technique reduces the third‐order intermodulation products in multichannel amplifiers when amplifiers operate closer to saturation. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

TD-SCDMA射频功率放大器研究

对采用时分双工模式的TD-SCDMA移动通信系统中的射频功率放大器的EVM性能进行了分析。通过分析功率放大器瞬态响应,得到射频功率放大器在时分双工模式下的EVM指标比频分双工模式下的EVM指标有所恶化的原因,并对基于MW6IC2240的射频功率放大器电路建立了一个二阶R-C模型,进一步分析了功率放大器件和外围电路的参数对功率放大器瞬态响应的影响,得到功率放大器瞬态响应的开关上升时间大小会影响时分双工模式下射频功率放大器EVM性能。基于此,提出了改进TD-SCDMA系统中射频功率放大器EVM性能的方法。改进后的TD-SCDMA射频功率放大器在时分双工模式下的EVM性能与频分双工模式时接近。     

Procedural CAD Model Edge Tolerance Negotiation for Surface Meshing

Geometrical models output from CAD software often require modification before they may be used for analysis-quality mesh generation. This is due primarily to the inconsistencies in tolerances used by the CAD operator and the tolerances required for analysis. This paper presents a method for construction of watertight surface meshes directly on imperfect non-modified CAD models. The method is based on a hierarchical grid topology structure that defines a surface mesh by a grid and a collection of curves defining the boundary. Curve boundaries on component surfaces are iteratively split and merged according to user-set tolerances, allowing adjacent surface meshes to become computationally watertight via their shared edge curves. The collection of watertight surface meshes may then be made model-inde-pendent through interactive agglomeration of the surface meshes, followed by refinement and decimation sweeps to remove artifacts of original surface edges. Interactive procedures used for difficult cases are also explained, as are ongoing efforts for further automation.     

Education and training for CAD in the auto industry

CAD-systems envisioned and remarkably well specified in the 1950s have powered themselves into the central role they enjoy in today's automotive industry through continuous improvements and technological breakthroughs. This paper emphasizes the parallel and continuing evolution in the training and educational needs of users of CAD-systems. In the context of early historical developments of CAD at General Motors, this paper categorizes CAD-users in the automobile industry and presents their current and future needs. The variance in their educational and training needs poses an ongoing challenge for educational and industrial institutions to meet.