Showing papers in "IEEE Microwave Magazine in 2001"

RF MEMS switches and switch circuits

Abstract: MEMS switches are devices that use mechanical movement to achieve a short circuit or an open circuit in the RF transmission line. RF MEMS switches are the specific micromechanical switches that are designed to operate at RF-to-millimeter-wave frequencies (0.1 to 100 GHz). The forces required for the mechanical movement can be obtained using electrostatic, magnetostatic, piezoelectric, or thermal designs. To date, only electrostatic-type switches have been demonstrated at 0.1-100 GHz with high reliability (100 million to 10 billion cycles) and wafer-scale manufacturing techniques. It is for this reason that this article will concentrate on electrostatic switches.

Linearization: reducing distortion in power amplifiers

Abstract: This article discusses techniques for the cancellation of distortion (linearization) in power amplifiers. Different methods of linearization are introduced and compared. The linearization of solid-state power amplifiers (SSPAs), traveling-wave tube amplifiers (TWTAs) and klystron power amplifiers (KPAs) are considered. Although the focus of this article is on power amplifiers, many of the techniques are applicable to other components such as mixers, low-noise amplifiers, and even photonic components, such as lasers and optical modulators.

RF fiber-optic link performance

Abstract: Applications that involve point-to-point routing of analog signals have benefited from the excellent propagation characteristics of optical fiber. Fiber-optic links that remote RF signals to and from phased-array radar antennas must meet especially stringent performance requirements. The past decade has seen significant progress in the performance of the fiber-optic links that distribute RF signals in antenna-remoting applications, as well as in cellular communications and cable television signal distribution networks. This article reviews the present state of the art in RF fiber-optic links.

Dielectric resonators raise your high-Q

Abstract: High-quality resonating elements are the key to the function of most microwave circuits and systems. They are fundamental to the operation of filters and oscillators, and the performance of these circuits is primarily limited by the resonator quality factor. At microwave frequencies, the quality factor (Q) of metal transmission line resonant circuits is proportional to volume. As a result, waveguide structures are often employed to increase Q at the expense of size, weight, and cost. Dielectric resonators overcome these limitations due to the fact that their losses are dominated by dielectric loss (loss tangent), and only in small part to metallic losses (housing). Dielectric losses are improving constantly, whereas metal losses, with the exception of superconductors, have remained substantially the same. These resonators can be made to perform the same functions as waveguide filters, but are, in contrast, very small, stable and lightweight. The popularization of low-loss dielectric resonators roughly coincides with the miniaturization of many of the other associated elements of most microwave circuits. When taken together, these technologies permit the realization of small, reliable, lightweight and stable microwave systems.

Vacuum electronics for the 21st century

Abstract: This article explores the history and diversity of this remarkable technology, with emphasis on advances in vacuum-electronic amplifiers, including the microwave power module (MPM), that have been enabled by the ongoing development of modeling and simulation tools These physics-based codes, enabled by rapid advances in computational hardware, allow simulation-based design and optimization of complex vacuum-electronic circuits The growth of satellite-based digital communications technology over the past decade has opened lucrative commercial opportunities for vacuum-electronic amplifiers This exciting new area requires the efficient production of high-frequency power and the ability to handle spectrally efficient modulations within stringent packaging constraints at affordable cost

Direct electromagnetic optimization of microwave filters

Abstract: This article explores an optimization procedure for microwave filters and multiplexers. The procedure is initialized by a classical filter synthesis based on a segmented electromagnetic synthesis that provides the basic dimensions of the structure. The optimization loop, which combines a global electromagnetic analysis and a coupling identification, improves the structure response compared to an empirical optimization.

Safety standards for exposure to RF electromagnetic fields

Abstract: Looking back at the past 40 years of development and forward to the new millennium, this article reviews the subject of safety standards for exposure to microwave/RF energy. The present standards are highly advanced with the use of modern dosimetry and a thorough computerized review of the literature. The bioeffects and hazards are predominantly thermal in nature and applicable standards, whether for exposure or product performance, incorporate large safety factors. These standards are the result of broad consensus among an appropriate balance of scientists, engineers, and stakeholders that results under the due process of the IEEE Standards system.

3-D integration of RF circuits using Si micromachining

Abstract: Micromachined silicon integrated circuits have the potential for providing an overarching circuit integration technology that can significantly reduce the size, weight, and cost of microwave and millimeter-wave components. The capability to integrate diverse substrate technologies opens the door for real multifunction chips, combining analog, digital, RF,and optoelectronic functions. This natural approach to three-dimensional (3-D) vertical integration not only can provide higher density circuits, but, by freeing RF circuit design from the tyranny of the two-dimensional (2-D) layout, can reach levels of performance not possible in a planar geometry. This article focuses on the concept of 3-D circuit integration using silicon (Si) bulk micromachining; however, similar techniques can be applied in any other III-V substrate material. Packaging issues prerequisite for the 3-D integration and component development that led to the capabilities for 3-D integration are discussed. The integration techniques are applied to a 3-D integrated W-band power cube, which provides a vehicle for successfully demonstrating the concept and basic techniques for 3-D integration. A concept study is presented of the use of micromachining to integrate Ka-band 2-D and 3-D corporate power combining architectures.

Specific absorption rates induced in head tissues by microwave radiation from cell phones

Abstract: The wireless telephone industry is concerned about how the public may use the SARs, because, according to one industry source, "SARs by themselves may be misleading and variations in SARs do not represent a variation in safety." Indeed, SAR values can vary as a function of carrier frequency (for example, 850 or 1,900 MHz, used to transmit the telephone message) or how the handset is held. The author gives some insights into SAR, what it is, how is it determined, and what it means.

Standards in IEEE 802 unleash the wireless Internet

Abstract: Within the Institute of Electrical and Electronics Engineers, Inc. (IEEE), the IEEE 802 LAN MAN Standards Committee is developing air interface standards for wireless local area network (LAN), wireless metropolitan area network (MAN), and wireless personal area network (PAN) technology. These standards are enabling the development of an infrastructure for the wireless Internet.

Health effects: the blood-brain barrier, cancer, cell phones, and microwave radiation

Abstract: A series of recent epidemiological studies has provided some optimism, in that they imply that the use of cellular mobile telephones does not cause brain tumors in the short term. It is also recognized that these investigations do not measure, in the long run, risks for cancers, such as brain tumors with longer latency periods of induction or slow-growing tumors that could take decades for symptoms to emerge in humans. Therefore, lifespan long research, using animal models, is crucial. The scientific evidence on cellular-telephone safety or harm remains inconclusive.

Heterojunction and heterodimensional devices for optoelectronics

Abstract: This article features a few optical sensory devices with basic properties that are changed by the presence of a two-dimensional electron gas (2DEG). A photodetector based on ohmic contact to the 2DEG is first presented in which variation of the 2DEG concentration and the (transverse) electric field that causes this confinement radically changes the device behavior. Next, the same device architecture is used but two Schottky contacts replace the ohmic ones, resulting, as expected, in a vastly different device behavior.

Advanced phase-locked-loop oscillators

Abstract: This article presents a very sophisticated subclass of communication subsystems, namely oscillators, that use the phase-locked loop (PLL) technique. Some basic features and several application examples are presented that enable locking in the oscillator signal for each frequency offset. If the oscillator is used on its fundamental frequency, a high spectral purity is achieved without additional distortion. Furthermore, it can be increased by the filter function of the loop. An integrated 70 GHz synthesizer is introduced and discussed, and a microwave synthesizer module and its technical behavior is described. Several measured results supported by analytical considerations show the applicability and the high performance of the PLLs introduced.

Woodwind design uses microwave theory

Abstract: Woodwind musical instruments consist of holes and tubes that enable a musician to play different notes. Woodwinds can be modeled with open holes as short circuits and tubes as transmission lines. An instrument can be designed by modeling all of the sections and fingering configurations. Transmission-line approximations and cascaded transmission-line theory can be used to model woodwind instruments, such as the flute, crumhorn and cornetto. In fact, the same transmission-line equations and approach of breaking a circuit into small sections are used for microwave circuit design. In this article, this approach is applied to design a crumhorn using commercially available Lucite tubing. After fabrication, good agreement is obtained between the measured performance and the theoretical predictions.

Microwave engineering education using web-based instruction

Abstract: The electronic information transfer revolutionizes the flow of information in a similar manner as the print material did over 400 years ago. The opportunity for mass production of the written knowledge has transformed the classical methods of teachings. Electronic publishing, with its free flow of knowledge, has already reshaped the structure of our libraries, and it is posed to influence not only the physical structure of the classroom but also the style and methods of teaching. Even the technical publications distributed by the Institute of Electrical and Electronics Engineers (IEEE) as journals or symposia digests are gradually moving to the electronic format. It is not too far off mark that, in a short time, the technical papers are going to merely be a movie clip of the actual experiments or numerical models of the reported paper. The IEEE Microwave Theory and Techniques (MTT) Society has led this campaign and is poised to provide the information-age benefits to its members. Since one of the primary responsibilities of any professional society is the continuing education of its members, it is natural to expect the MTT Society to initiate educational initiatives. As a result of advances in telecommunication and the popularity of the Internet, electronic multimedia now could augment the traditional teaching methods. Hence, the Education Committee initiated the Microwave Multimedia Module (M4) project, in addition to many other efforts. The Drexel University team of Mohammed-Reza Tofighi, a Ph.D. student, and myself has responded to the M4 project challenge. Our goal is to develop an E-book that covers various topics in passive and active microwave circuits in the hope of assisting MTT Society members in their continuing education efforts. This product is developed as standard “post page” and will be completed in mid-2001. The copyrighted material will then be delivered to IEEE as an electronic book.

Risk of human exposure to cellular mobile communication radiation

Abstract: Most of our knowledge concerning the biological effects of radio frequency (RF) radiation from wireless communication devices has come out of investigations conducted using experimental animals, such as rats, mice, etc. When it comes to the impact of RF radiation on human health and safety, epidemiology can play a pivotal role because it is a study of the distribution of disease and its determinants in human populations. To examine if exposure to wireless communication radiation is involved in cancer induction and promotion, it is necessary to collect data from people with similar backgrounds, other than RF exposure.

Coupling effects between lumped elements [MMICs]

Abstract: The coupling effects between various lumped elements have shown that the effect on inductors is less than 1% for inductors having reactance of about 50 /spl Omega/ and separated by 20 /spl mu/m on a 75 /spl mu/m thick GaAs substrate. Thus, a distance of 20 /spl mu/m between lumped elements is safe for monolithic circuits at RF frequencies.

Transimpedance amplifiers for optoelectronic applications

Abstract: In this application note, the fundamental characteristics and issues related to the design of transimpedance amplifiers for optical receivers have been presented. Guidelines for the design of distributed transimpedance amplifiers have been outlined. The analysis of the uncompensated distributed transimpedance amplifier has clearly identified the problems limiting the performance of the amplifier. The negative resistance compensation technique has been shown to provide a solution to overcome the performance limitation.

Microwave surfing - which came first: big bang or big crunch?

Abstract: Microwave radio astronomy has been one of the driving forces behind the spectacular success of the "standard" account of the origin of our universe, popularly known as the inflationary "Big Bang" theory This article briefly reviews a few concepts in the field including the discovery of the cosmic microwave background, the cosmic background imager, the degree angular scale interferometer, the grafting of "dark energy" onto the prevailing inflationary Big Bang model, and the conception of the cyclic universe paradigm

Application notes: what's my impedance?

Abstract: Although a lot of attention has been focused on the very capable and expensive 2.5-D and 3-D field solvers, there are many useful problems that can be done easily and quickly with an inexpensive 2-D cross-section solver. After a quick introduction to impedance calculation, we solved some basic microstrip and stripline problems. Any time you are learning to use a new tool, it is prudent to solve a few problems where the correct answer is known. Then you can move on to more interesting problems, like the CPW with overlay example and the shielded stripline example. This article was not intended to be a comprehensive review of these software packages, but rather a brief introduction to the concepts needed to calculate static transmission-line impedances.

Nano- and microelectromechanical systems [Book Review]

Abstract: S ergey Edward Lyshevski obviously has a lot of experience to draw on for this book. He has published many papers on microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS). This book is designed to be a one-semester course on MEMS and NEMS and possibly serves as the text for one of Dr. Lyshevski’s courses at Purdue University. While the book focuses on sensor, motor, and control applications, the author also tries to be comprehensive in all aspects of MEMS operation. The book begins with a NEMS and MEMS overview and proceeds to chapters on mathematical models, structural design, and system control. The mathematics used in Chapter 2 range from the differential equations of electrostatics, to Lagrangian dynamics, then on to quantum mechanics, and finally ending with two pages on heat diffusion. Biological analysis is brought in via molecular bond logic used for NEMS, and modern computer-aided design products such as SimuLink andMEMSCAD are mentioned.

What is RF

Abstract: It seems RF will remain a popular phrase for some time to come. Components and circuits whose design share a number of these concerns are RF, regardless of the numerical value of the frequency or bandwidth of electromagnetic signals involved. With a definition based on the designers' mind-set, we can include many kinds of components under the umbrella of RF at virtually any frequency from LF to IR.

Wireless investor [fundamental and technical analysis]

Abstract: The income-, value-, growth-, momentum-, and mania-driven styles have been explained, and the thinking behind each style outlined. These investing styles use various techniques associated with "fundamental" analysis and "technical" analysis. The goals for this issue are as follows: explain the difference between fundamental analysis and technical analysis; review the academic argument that technical analysis has no value; and provide a high-level overview of the basic techniques of technical analysis.

Printed inductors on alumina substrates

Abstract: Fabrication of printed inductors on alumina substrate using circular and rectangular shapes of multiturn inductors were studied. The values of the inductors were found to be close to the design values. Inductors with 6 mil spacing were found to be closer to the design values than the 4 and 5 mil of spiral inductors. It may be because of the mutual inductor effect between the turns. Q values of the smaller inductor are comparable to the discrete values. Low-pass filters built using printed inductors between 100 and 400 MHz cut-off frequencies provided close to the simulated performances in which discrete component model were used.

Microwave surfing. Wireless networks: an electronic battlefield?

Abstract: Dealing with covert surveillance and jamming may seem business as usual to microwave engineers working in the defense sector, but the same issues will appear rather remote to their colleagues in the wireless business. However, as the reports given suggest, wireless network designers may need to use their own countermeasures to avoid being ambushed on the electronic battlefield.