Showing papers in "IEEE Microwave Magazine in 2008"

Space mapping

Abstract: In this article we review state-of-the-art concepts of space mapping and place them con- textually into the history of design optimization and modeling of microwave circuits. We formulate a generic space-mapping optimization algorithm, explain it step-by-step using a simple microstrip filter example, and then demonstrate its robustness through the fast design of an interdigital filter. Selected topics of space mapping are discussed, including implicit space mapping, gradient-based space mapping, the optimal choice of surrogate model, and tuning space mapping. We consider the application of space mapping to the modeling of microwave structures. We also discuss a software package for automated space-mapping optimization that involves both electromagnetic (EM) and circuit simulators.

Bulk acoustic wave RF technology

Abstract: In this article, we will provide an overview of BAW filter technology by discussing comparison between BAW and SAW RF filter technologies, working principles of BAW resonator and filter, BAW resonator key performance parameters, comparison between free-standing bulk acoustic resonator (FBAR) and solidly mounted resonator (SMR) technologies, status of BAW resonator design and models, BAW filter manufacturing challenges, and future BAW technology improvement directions.

Be flexible

Abstract: The first section of this article gives an overview of standards that current multimode cellular phones must support. The paper then covers traditional analog architectures that were dominant in the SiGe-BiCMOS era and were also the basis for the first CMOS-based transceivers. Then the paper focuses on the extension to these architectures utilizing digital front-ends (DFEs) to enhance their flexibility and configurability. The final section gives an outlook to upcoming developments for CMOS nodes beyond 130 nm like all-digital phase locked loops (ADPLL) and sampling receivers.

A practical guide to 3-D simulation

Abstract: This article is intended to give design engineers an overview over some properties of numerical methods used in today's most relevant commercial electromagnetic (EM) simulation tools. It cannot and does not want to be a rigorous analysis of the methods themselves nor a concise description of their history.

VNA calibration

Abstract: The paper presents the improvements, as well as the calibration, on state-of-the-art of measurement made using vector network analysers.

RFID Transponders

Abstract: The objective of this article is to review radio frequency identification (RFID) technology, its developments on RFID transponders, design and operating principles, so that end users can benefit from knowing which transponder meets their requirements. In this article, RFID system definition, RFID transponder architecture and RFID transponder classification based on a comprehensive literature review on the field of research are presented. Detailed descriptions of these tags are also presented, as well as an in-house developed semiactive tag in a compact package.

Multisine signals for wireless system test and design [Application Notes]

Abstract: Multisine signals are used in the laboratory and in the field to provide a periodic, well-characterized waveform that can simulate complex modulated radio frequency (RF) signals. In the field of wireless telecommunications, multisines are often used to provide realistic test signals that have statistics similar to various types of digitally modulated signals. It is concluded that the multisine approach is well suited for evaluating a nonlinear system excited by real communication signals. Multisine signals enable to gather important information about the in-band distortion and to excite long-term memory effects by generating baseband components. They are periodic and straightforward to characterize, making them ideal for identifying both magnitude and phase distortion during test and verification. Using multisines to simulate standard wireless system excitations and figures of merit allows for very good laboratory nonlinear distortion measurement setups.

Roadmap of IMT-advanced development

Abstract: The WRC-07 decisions have paved the way toward the development of IMT-advanced by identifying a 200-MHz contiguous spectrum above 3 GHz for a number of countries. It is also noted that for early implementation of IMT-advanced there are technical subjects to be studied and solved, in particular for compatible operation with other systems sharing the same frequency bands. For the standardization activities, global cooperation between ITU-R and other organizations are required.

Combining Coarse and Fine Models for Optimal Design

Abstract: In this article we reviewed the implicit space mapping concept. We illustrated it using a simple tapped-line microstrip filter example. We demonstrated the robustness of our approach by performing an accurate design of a microstrip hairpin filter. A detailed and easy-to-follow design optimization procedure was provided and the Agilent ADS implementation of the algorithm was described. A good electromagnetically validated design in Sonnet em was obtained in a few fine model simulations. Implicit space mapping is a simple approach to combine a circuit-theory based CAD model and an EM simulator model to achieve fast and accurate optimal design and modeling.

Toward Integrated Circuit Size Reduction

Abstract: In this article, voltage-basis, current-basis, and normalized scattering matrices were introduced and it was shown that three different scattering matrices are the same only with equal termination impedances but only the normalized scattering matrix is correct with arbitrary termination impedances. The scattering matrices can be calculated from impedance, admittance, or ABCD matrices characterizing a network. However, if the network has more than three ports, the calculation process from the admittance or impedance matrices is not simple. For this, conversion formulas of the ABCD parameters into the normalized scattering parameters were presented for the impedance-transforming directional couplers. If one can have any choice of the termination impedances of the directional couplers as shown in this article, the total size of a microwave integrated circuit can be reduced.

Low-temperature cofired ceramic LC filters for RF applications [Applications Notes]

Abstract: Over the past few years, a great amount of effort has been spent on LTCC filters or related research [21]?[28]. Some of these components have more advanced functionalities, such as a combination of filter and balun, or a complete front-end module with balun, filter, and matching network. At the same time, advanced methodologies have also been developed to design these components [29]. All the enjoyment of miniaturized RF components or modules is due to the promising three-dimensional design flexibility of LTCC technology. It is expected that a variety of functionally complex components will be continuously available on the market such that the cost and size of the overall wireless terminal can be further reduced. Various aspects of designing miniaturized LTCC LC filters have been briefly discussed here. Conventional coupled LC resonators are commonly used in LTCC filters for RF applications because of their compact size advantage. The shunted parallel resonator in this type of filter can be realized directly as a lumped-element or distributed quarter- wavelength stripline with or without loaded capacitors. Filters with distributed resonators in general have better passband insertion loss performance. Moreover, there are many ways to improve the rejection performance in an LTCC filter design; for example, by modifying the resonators or admittance inverters so as to introduce transmission zeros at the stopband. It was demonstrated, through a design example, that by making use of the flexibility of LTCC technology, a compact LC bandpass filter can be realized for various RF applications.

New-Wave Radio

Abstract: Radio communications in the past century have relied primarily on nonlinear devices to modulate and demodulate signals for wireless transmissions. This article reviews initial laboratory results obtained with new radios using linear interferometers to modulate and demodulate ultra-wide-band (UWB) signals. Automotive and chip fabrication industries apply such interferometers in new commercial radios for UWB communications.

Measurement of microwave behavior in optical links

Abstract: The aim of this article is to give an overview of how S-parameter techniques can be used and misused to measure the "microwave behavior" of microwave photonic components and links-a field known as lightwave component analysis. Along the way, we clarify what is meant by the term "microwave behavior" when it is applied to what in effect are nonmicrowave components. We find that while it is desirable to extend the S-parameter approach to the lightwave domain, it is not as easy as we would hope.

Multiport VNA measurement

Abstract: This article presents some of the most recent multiport VNA measurement methodologies used to characterize these high-speed digital networks for signal integrity. There will be a discussion of the trends and measurement challenges of high-speed digital systems, followed by a presentation of the multiport VNA measurement system details, calibration, and measurement techniques, as well as some examples of interconnect device measurements. The intent here is to present some general concepts and trends for multiport VNA measurements as applied to computer system board-level interconnect structures, and not to promote any particular brand or product.

Artificial Dielectric Resonators for Miniaturized Filters

Abstract: This paper discusses about miniaturization of microwave resonators based on the artificial dielectric concept. Very high effective permittivity will contribute to reduce the dimension of resonators significantly, though the unloaded Q is deteriorated. Its recovery should be possible by controlling the thickness of metal strips.Another feature of artificial dielectrics, easy control of anisotropy and inhomogeneity, will improve the spurious property of the resonator. Artificial dielectric is suitable to be implemented in the LTCC technology. Some examples were described, though there is more room for improvement of spurious and loss property. The concept of artificial dielectrics is related to that of coupled resonators. Control of mutual coupling between resonators creates a new type of resonator. The improvement of loss property is a key issue for the application of artificial dielectrics, and it is now being studied by our group. The same thing is also true for metamaterials, as long as the unit particles are made of metal strips.

Shrinking microwave filters

Abstract: An adaptive predistortion technique has been presented and verified through the design and fabrication of practical filters in both the C and Ku bands. The method allows the realization of microwave filters at a lower cost, lighter mass, smaller volume, and better performance with minimum insertion loss penalties.The concept of lossy filters has been presented from a practical perspective. A simple lossy synthesis technique using any synthesized lossless (nontransversal) filter was shown, which can be used with hyperbolic rotations for loss distribution. Moreover, the limitation on the minimum Q of lossy resonators has been studied using a one-pole filter as a fundamental building block. Lossy four-pole Chebyshev and quasi-elliptic synthesis examples were presented. A four- pole Chebyshev lossy filter in the Ku band has been synthesized, modeled, and fabricated successfully using mixed combline and microstrip technologies. The design has the advantage of having all input-output paths going through more than one resonator, which minimizes unwanted source-to-load coupling, especially at high frequencies. The lossy approach is still at its early stages of development and needs more research and development effort to become as mature as the predistorted filters.

Coplanar waveguide basics for MMIC and PCB design

Abstract: In this article, basic CPW design information geared towards a practicing microwave circuit designer, including the applicability and benefits of CPW transmission line configuration, design and modeling tips, and two microphotographs of implemented CPW MMIC amplifiers are provided. Supported by the CPW geometry (coupled slotline) and modes that can occur for practical implementation of CPW (parallel-plate waveguide mode). CPW has a significant number of applications in microwave design, and we hope this brief tutorial will provide enough of an introduction to aid designers in beginning CPW design.

Practical Magic

Abstract: Typically, Doherty test fixtures are inflexible with regard to combiner positioning. The generic Doherty development fixture shown here can quickly provide the designer with the final circuit requirements for multiple devices. The dynamic Doherty combiner enables this flexibility by using the 50-Omega line as part of the output transformation. An easy-to-implement 50-Omega line and a shunt cap provides the transformation required from the Doherty inverter to the amplifier output. Final circuit configurations can revert to the traditional lambda/4 transform once the phase length "Oslash" is identified. Flexible Doherty development circuits will assist in minimizing the fixtures required for development efforts. This Doherty development process is easy and straightforward to implement, and results can be obtained quickly. Simulation methods and models will continue to be used to create the 50-Omega tuning structures and optimize the design of Doherty circuits. However, this practical design approach can be applied for each circuit that needs to be designed, and good results will be obtained.

Shortening the design cycle

Abstract: Electromagnetics (EM) has today become a critical part of the microwave design cycle. This article briefly traces the entry of EM into microwave design and describes how today's design cycle arose. Then, we discuss how recent developments (in particular, perfectly calibrated ports in EM analysis) open entire new areas of applied microwave design.

Introduction to measurements for power transistor characterization

Abstract: In this article, we will introduce you to measurements for power transistor characterization: why they matter, why they are such a complicated, highly specialized field, and where we think the technology of power transistor characterization is headed. The characterization of microwave power transistors is an important and emerging field with many interesting engineering challenges. One can basically distinguish two areas: model extraction measurements and model validation measurements. To make things simple, isothermal pulsed-bias pulsed S-parameter measurements are typically used for model extraction purposes and load-pull measurements are typically used for model validation purposes. Both areas are rapidly evolving in order to keep track of new power transistor technology. The main issue with pulsed-bias pulsed S-parameter characterization is the need to apply pulses with ever-increasing amplitude (up to 200 V and 10 A) and ever-decreasing pulse width (smaller than 400 ns). The load-pull measurements can be done with a variety of setups, with active or passive approaches, and with or without handling harmonic frequencies. The challenges of load-pull system development are to offer time-domain voltage and current waveforms at the transistor terminals-an invaluable tool to provide insight in highly nonlinear transistor behavior-in addition to the capability to present low input impedances (1 Omega) and to handle high power levels (up to 100 W).

Industrial design of axisymmetrical devices using a customized FDTD solver from RF to optical frequency bands [Application Notes]

Abstract: This article focused on the vector two-dimensional finite-difference time-domain (V2-D FDTD) method for axisymmetrical devices, also known as BOR FDTD. The approach to solving Maxwell equations by the V2-D FDTD method is straightforward. Not only the whole structure simulation is feasible, facilitating a search for globally optimum solutions, but also a valuable insight is provided into the subtleties of the device operation in the 3-D space and time. A graphical interface of the QW-V2D solver has been used to exemplify how the software helps in problem solving and quick search for new solutions.

Fine-tuning commercial and military radio design

Abstract: Software-defined radio (SDR) and cognitive radio (CR) concepts have been introduced to change the paradigm of wireless communications by making it possible to improve data throughput and connectivity by enabling autonomous reconfigurability spectral and temporal agility, and adaptive behavior. This new class of intelligent radio would be able to adapt to a wide variety of wireless operating conditions and multiple protocol standards, which will allow collaboration between otherwise incompatible systems.

Rotman lens design and simulation in software [Application Notes]

Abstract: Since its invention in the early 1960s (Rotman and Turner, 1963), the Rotman Lens has proven itself to be a useful beamformer for designers of electronically scanned arrays. Inherent in its design is a true time delay phase shift capability that is independent of frequency and removes the need for costly phase shifters to steer a beam over wide angles. The Rotman Lens has a long history in military radar, but it has also been used in communication systems. This article uses the developed software to design and analyze a microstrip Rotman Lens for the Ku band. The initial lens design will come from a tool based on geometrical optics (GO). A second stage of analysis will be performed using a full wave finite difference time domain (FDTD) solver. The results between the first-cut design tool and the comprehensive FDTD solver will be compared, and some of the design trades will be explored to gauge their impact on the performance of the lens.

Radar Revisited (review of "Radar Handbook, 3rd ed." by Merrill Skolnik) [Book Reviews]

Abstract: This is the third edition of an established handbook, edited by one of the most-recognized names in the field of radar technology. The volume is a compilation of 26 chapters, authored by individuals with a thorough command of, and incredible credentials in, the topics of their chapters. Most chapters have a large number of figures (up to several dozen) and extensive bibliographies. Chapters range from fairly quantitative and mathematical ones to cursory and descriptive ones. Some sections of the handbook represent a concise and readable summary of the state-of-the-art of knowledge on their topics; others are a sketchy collection of remarks for which it is difficult to identify the benefits to be derived by the reader. There is little coordination between chapters where similar topics may be discussed, and a lack of any cross-referencing. There are also weaknesses in the index, as well. While the older, classical radar topics receive much attention, the book overlooks newer areas such as coverage of automotive radars. This volume will appeal to the generalists with interest in the conventional radar subjects, and to others as a starting point for locating sources with more detailed information.

HBT Modeling

Abstract: III-V heterojunction bipolar transistors (HBTs) enjoy several advantages over their conventional silicon cousins. These include: (1) a thinner base and lower base resistance which yields higher gain and fmax; (2) high breakdown voltage; (3) low parasitics; (4) high power density. The combination of a thin base (higher fT), low base resistance (higher fmax), and low parasitics in particular make HBTs a suitable choice for high- frequency applications.

Stopband filters built in the BAW technology [Application Notes]

Abstract: This article presented the design of two band reject filters in the BAW technology. The two designs show different benefits. The ladder T topology has a better rejection bandwidth than the ladder topology because the bandwidth is controlled by resonance and antiresonance frequencies, which are selected by the loading layer. Moreover, the bandwidth is adjustable by the design. This setup presents a steeper rejection slope. The insertion loss can be reduced by increasing the bottom electrode's thickness. However, the fabrication process and the control of resonance frequency are more difficult since antiresonance frequencies of series resonators depend on the thickness of the loading layers.

When self-consistency makes a difference

Abstract: Compound semiconductor power RF and microwave device modeling requires, in many cases, the use of self- consistent electrothermal equivalent circuits. The slow thermal dynamics and the thermal nonlinearity should be accurately included in the model; otherwise, some response features subtly related to the detailed frequency behavior of the slow thermal dynamics would be inaccurately reproduced or completely distorted. Two examples have been shown, concerning current collapse in HBTs and modeling of IMPs in GaN HEMTs. Accurate thermal modeling can be made compatible with circuit-oriented CAD tools through a proper choice of system-level approximation; in the discussion presented it exploited a Wiener approach, but of course the strategy should be tailored to the specific problem under consideration.

True broadband multimedia experience

Abstract: Even though the fourth-generation (4G) wireless story has not yet been defined, it is clear that the industry is moving aggressively to a 4G world. The pace of 4G adoption as well as the rate at which standards are being developed is by far the fastest of all previous generations of wireless. Whereas it took nearly ten years for third-generation (3G) to roll out and become standardized, 4G activities are proceeding on a much faster three-year cycle.

Tailoring FEKO for microwave problems

Abstract: In this article we have presented some of the more recent modeling options available in FEKO (waveguide ports, combination with FEM, dielectric GO, PBCs, coupling with networks) that are specifically useful to the microwave engineer. In addition to presenting some of the theory, we focused on examples to show the application of each method and discussed their advantages. The examples were kept intentionally simple such that the relevant advantages can easily be highlighted.