bluuebunny/crossref_metadata_2025 huggingface dataset:
Large complexes and molecular machines by electron microscopy
Authors: Plitzko J. M. , Engelhardt H.
Published: April 2005

Cryo‐electron tomography has the unique potential of visualizing the structure of large protein complexes in isolated preparations at high resolution and in their natural context, in unperturbed cells. Tomograms of vitrified cells are essentially three‐dimensional images of their entire proteome. They contain the information of the spatial relationship of macromolecules, their interactions, and reveal the assembly of macromolecular machines that are only stable in vivo. Here, we present a brief survey of the principles and developments of cryo‐electron microscopy and image reconstruction.
Genome maps and their use in sequence assembly
Authors: Dear Paul H.
Published: April 2005

Genome maps give the location of defined sequence features in the genome and serve as a framework around which to assemble the complete genome sequence. Without them, the complete assembly of complex genomes purely from the shotgun sequence data is effectively impossible. Here, I summarize the principle methods that are used to make detailed genome maps and the ways in which mapping and sequencing are integrated to produce finished genome sequences.
Eukaryotic regulatory sequences
Authors: Krull Mathias , Wingender Edgar
Published: April 2005

The existence and clustering of particular regulatory sequences is the main determinant of specific gene expression. While the sequences of whole genomes for several species are now available, information on those control elements is relatively sparse. The numerousness of elements in the genome limits experimental identification. In‐depth knowledge on DNA binding sites of transcription factors and their role in regulatory modules will enable genome‐wide in silico site prediction with high sensitivity and specificity. Here we present a short review of the types of regulatory sequences and the computational methods that are applied for their characterization and prediction.
Molecular simulations in structure prediction
Authors: Fraternali Franca , Kleinjung Jens
Published: April 2005

Structure prediction projects fill the gap between the number of known sequences and experimentally determined structures. While providing valuable medium resolution models, refinement by molecular simulations could improve structures to high resolution.
Threading algorithms
Authors: Bienkowska Jadwiga , Lathrop Rick
Published: April 2005

This chapter reviews various algorithms that have been developed for protein structure prediction by threading. Threading algorithms depend on many features of protein sequence and structure representations and not all of them are used by all methods. There is no standard formalism to represent those different features. While providing necessary detail, sometimes the formal notation obscures the core idea of an algorithm. In order to make the core ideas transparent to many readers, we made an effort to adhere to a simple formalism and tried to avoid mathematical formulas. This forced us to omit many details and complete outlines of algorithms, for which the reader is referred to the original literature for a detailed picture.
RNA
secondary structure prediction
Authors: Mathews David H. , Zuker Michael
Published: April 2005

The field of RNA secondary structure prediction matured in the last 10 years with the development of many readily available software packages. The thermodynamic parameters for predicting the free energy of an RNA secondary structure are continuing to be revised on the basis of new experiments. This article reviews the available secondary structure prediction algorithms for both a single sequence and multiple sequences.
Simulation of biochemical networks
Authors: Kierzek Andrzej M.
Published: April 2005

Advances in experimental techniques of molecular biology motivate attempts to mathematically model complex biochemical reaction networks occurring in the cell. Usually, the models are so complex that they cannot be solved analytically and so computer simulations must be employed. Biochemical reaction networks may be expressed as a system of differential equations, thus allowing standard algorithms and software packages to be used in the simulation. Frequently, the lack of precise model parameters prevents quantitative studies of the system dynamics. In such cases, qualitative simulations using logical formalism or the study of flux distribution of the stationary state may be performed. The methods mentioned above are deterministic and do not take into account stochastic fluctuations resulting from the fact that biochemical processes occur in very small volumes. Various Monte Carlo approaches are used to account for the stochastic effects in the dynamics of biochemical reaction networks. Recent advances in these methods allow simulations of systems composed of reactions varying by many orders of magnitude in their rates and the number of molecules involved. Simulations explicitly incorporating positional information on the spatial clustering of membrane receptors have also been performed.
Altimeters
Authors: Eren Halit
Published: April 2005

Alimeters are instruments that measure altitude or elevation objects above or below a given level. There are three types of alimeters: pressure altimeters that make use of properties of atmosphere, radio and radar altimeters that are based on electromagnetic wave propagation, and optical altimeters that use optical properties of light and lasers. All these basic altimeters find extensive applications in industry, aviation, military, navigational aids, land surveying, remote sensing, recreations, and sports.

Modern barometric altimeters are manufactured mostly as integrated circuit (IC) pressure transducers. Therefore primary signal processing such as linearization, error corrections, and gain adjustment are made within the chip. Altimeters based on electromagnetic principles transmit electromagnetic energy and detects of the reflected energy from an object. An example of these altimeters is the single‐frequency radar system that broadcasts a pulsed tone signal directly downward the object and processes the returned signals with elaborate electronic circuits for high sensitivity and resolution. Altimeters based on microwave energy transmission can be used for other purposes such as imaging, scanning, mapping, oceanographic studies, and weather forecasting. Laser altimeters operate similar to the radar altimeters by processing time differences between the transmitted and received signals. Typical examples of such altimeters are the LIDAR (light detection and ranging) and the SLA (shuttle laser altimeter) and RASCAL (
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A popular system that can be used as altimeter is the Global Positioning System (GPS), which constitutes 24 satellites orbiting around Earth. Each satellite transmits electromagnetic energy carrying unique codes and information. Information picked up receivers is used to determine positions of objects in three dimensions.
Amplitude Shift Keying
Authors: Xiong Fuqin
Published: April 2005

Amplitude shift keying (ASK) is one of the earliest and simplest digital modulations used in telecommunications. The simplest form of ASK is theON–OFFkeying (OOK). To improve bandwidth efficiency,M‐ary ASK (MASK) must be used. MASK can be coherently demodulated and noncoherently demodulated, and the former has a lower bit error probability but a more complex demodulator. The signal expression, power spectral density, block diagrams of modulators and demodulators (coherent and noncoherent), and bit error rate, are described in detail for each ASK scheme. Comparisons are made between various ASK schemes and between coherent MASK and the popular MPSK (M‐ary phase shift keying). Advanced ASK‐based modulation schemes, namely, QAM (quadrature amplitude modulation) and coherent and noncoherent ASK‐OFDM (orthogonal frequency‐division multiplexing) are also briefly described.
Antenna Accessories
Authors: Alves Plinio R. G. , Menezes Leonardo R. A. X. , Carvalho Paulo H. P. , Silva Franklin C.
Published: April 2005

Accessories in antennas can be seen as devices adapted to radiating or receiving electromagnetic wave structures. Their main purpose is to create means for the perfect operation of antennas. The accessories interconnect these antennas to the transmission and reception systems in an efficient and safe way. An electromagnetic coupling generally exists between the antennas and the accessories, and one can explore them to improve antenna performance. In this way, the accessories are as fundamental as the antenna proper, whose behavior is dependent on the appropriate connections.

Several kinds of accessories, are used more frequently: attenuators, baluns, chokes, coaxial (coax) lines, insulators, lightning arresters, planar structures, phase shifters, and twin‐lead devices. These components will be described in the following sections.
Antenna Compact Range
Authors: Kefauver W. Neill
Published: April 2005

The antenna compact ranges is a powerful tool employed to measure the performance of antennas accurately, efficiently, and with minimal facility investment. The term “compact” comes from the concept that an antenna can be measured without using a long outdoor range; hence the range is compact or small. The performance of these ranges has improved dramatically since the mid‐1970s and range designs have improved almost as rapidly as the modeling tools to design antennas since the reflector and feed designs are tied to many of the developments in high‐performance antennas.
Antenna Feeds
Authors: Bird Trevor S.
Published: April 2005

The term “antenna feeds” describes many types of antennas in common use today. Feeds are a means of supplying energy to (or receiving energy from) a secondary antenna, such as a reflector, lens, or beam waveguide, via a transmission line or waveguide. Everyday applications of antennas with feeds include satellite communications, radar, radio telescopes, deep‐space probes, and terrestrial microwave and millimeter‐wave radiolinks.

After a brief historical introduction, the basic characteristics of antenna feeds are explained. Then specific feed types are described under four main headings, namely aperture, linear, traveling‐wave and compound antennas. The approach adopted combines a short description of physical attributes with an outline of possible applications.

The class of aperture antennas is the most extensive, and details are given of various circular and rectangular waveguides and horns, self‐supporting feeds, and microstrip patches in feed applications. Linear antenna feeds such as the Yagi–Uda, logperiodic, and zigzag arrays are reviewed and properties of importance highlighted. Under the heading of traveling‐wave antennas, the antennas discussed include the dielectric rod, profiled‐slot, Vivaldi antennas, and linefeed antennas for cylindrical and spherical reflectors. Finally, the antennas covered in the compound feeds category are arrays, beam waveguides, splash plates, and dichroic reflectors.

Antenna feeds are linked intrinsically with feed systems, and some examples given are diplexers, beamforming networks, and comparator networks for monopulse tracking.

The article concludes with an outline of modern design methods of importance of feed antennas and some predictions of possible future developments.
Antenna Parameters
Authors: Balanis Constantine A.
Published: April 2005

This article summarizes the parameters of antennas, and it has been written as an introduction for the technologist and as a review for the antenna expert. It defines the most important parameters of some antennas in words and of others, using equations employed by antenna engineers for the analysis and design of antennas, especially for RF and microwave bands.
Antenna Scanning Arrays
Authors: Mailloux Robert J.
Published: April 2005

Electronic scanning arrays provide high‐gain radiated beams that can be directed to chosen spatial angles by the use of phase shifters or time‐delay units. This feature satisfies an increasing number of applications, from the military need for large arrays for ground‐based, airborne, and space‐based radars and communication systems, to the growing needs of the wireless community for much smaller, often adaptively controlled arrays. This article describes the fundamental properties and limitations of array antennas, including the parameters that constrain their gain, beamwidth, and bandwidth, and the phenomena of grating lobes. Several examples of pattern synthesis and adaptive control algorithms are presented. Last, there is a description of array architectures as appropriate to the three basic means of control, using analog, optical, and digital means of beamforming.
Antenna Radiation Patterns
Authors: Chryssomallis Michael T. , Christodoulou Christos G.
Published: April 2005

The radiation pattern of an antenna is one of the antenna's basic properties since it shows how the antenna distributes its energy in space. It generally consists of a number of lobes, and if it is measured far away from the antenna, it is independent of distance. It is a function of angles and can be expressed as field or power pattern. It usually can be completely specified from the patterns in two planes, perpendicular to each other, theEandHplanes, respectively. Related to the radiation pattern of an antenna, a number of important parameters exist, such as radiated power, radiation efficiency, directivity, gain and antenna polarization.

The subject of this article is to provide an introduction to radiation patterns and all the related important parameters. The content is organized in four sections. Section 1 introduces several antenna patterns, giving the necessary definitions and presenting the common types. The field regions of an antenna are also pointed out. In Section 2, after the introduction of Poynting vector and radiation power density, radiation performance measures such that the beam solid angle, directivity, and gain of an antenna are defined. In Section 3, the concepts of wave and antenna polarization are discussed. Finally, in Section 4, a general case of antenna pattern calculation is considered, and numerical solutions are suggested for radiation patterns that are not available in simple closed‐form expressions.
Antenna Testing and Measurements
Authors: Kefauver W. Neill , Martin Lockheed
Published: April 2005

Although extensive modeling codes exist to predict antenna performance, no model can certify hardware without some obtaining representative patterns of the antenna as it will be used. Extensive facilities using various methods to evaluate antenna performance have been developed over many years. This article covers the accepted technologies that allow verification of design performance.
Antennas
Authors: Christodoulou C. G. , Wahid P. F.
Published: April 2005

This article provides an overview of the characteristics of various antennas used in the RF/microwave region. A brief history of antennas is presented. Starting from simple wire antennas, the article goes on to describe reflector antennas, lens antennas, horn antennas, frequency‐independent antennas, conformal antennas, and reconfigurable antennas. The salient properties of each of these antennas are presented and discussed.
Antennas for Medium‐Frequency Broadcasting
Authors: Rackley Ronald , Folkert Matthew
Published: April 2005

Since the 1940s, there has not been significant development in the area of the antenna element itself as selfsupporting and guyed radiating towers continue to be used much as they were at that time.

New developments have principally involved auxiliary equipment used to test and monitor the antenna system and the means by which the antenna is theoretically analyzed. Digital antenna monitors are used today to accurately monitor the relative current magnitudes and phase relationships of the towers in a directional array while portable solid‐state field strength meters are used to measure radiation patterns. Advances have also been made with improved RF current meters, sampling transformers, and impedance measuring equipment. The design of medium‐frequency broadcast antennas for optimized performance has also seen tremendous advances with the introduction of numerical solutions to electromagnetic problems and nodal modeling of feeder systems made economically possible with personal computers vastly simplifying both design and implementation.
Backscatter
Authors: Ufimtsev Pyotr Ya.
Published: April 2005

The backscatter, or backscattering, is the scattering of waves back toward the source of the incident wave. This process substantially depends on material properties of the scattering object, its shape, size, and spatial orientation relative to the incident wave, as well as on the frequency and polarization of the incident wave. One distinguishes three frequency regions with different physical properties of scattered waves. They are quasistatic, resonance, and quasioptical regions.
Buried Object Detection
Authors: Türk Ahmet Serdar , Hocaoglu Ali Köksal
Published: April 2005

The subsurface detection and identification of the buried geologic and synthetic (human‐produced) structures is currently an important research area. The scope of the problem is very complex and covers a wide range in applications. One area of the research includes the detection of a large metallic gas pipe buried in a deep or small plastic mine laid just beneath the ground. The size, geometry, constitution and depth of the target object and the characteristics of the medium (wet soil, sand, etc.) can be considered as the principal parameters for the detector designs. In this article, different sensor technologies based mainly on electromagnetic, acoustics, infrared, or chemical theories are discussed.
Cellular Radio
Authors: Lee William C.Y.
Published: April 2005

The cellular radio system is sometimes called a mobile phone system or a car phone system. Due to the daily needs of subscribers, cellular systems have expanded considerably all over the world. This article discusses the history of cellular systems and the difficulty of deploying them in the mobile radio environment, elaborating on employing digital cellular systems, Personal Communication Services (PCS) mobile satellite systems, and the future IMT‐2000 system.
Chirality
Authors: Lakhtakia Akhlesh
Published: April 2005

Chiral media have the ability to discriminate between left‐handed and right‐handed electromagnetic fields. These media can be classified into two types: (1) isotropic chiral media and (2) structurally chiral media. The molecules of a naturally occurring isotropic chiral medium are handed, while an artificial chiral medium can be made by randomly dispersing electrically small, handed inclusions (such as springs) in an isotropic achiral host medium. The molecules or inclusions in a structurally chiral medium, such as a chiral nematic liquid crystal, are randomly positioned but have helicoidal orientational order. Structurally chiral media can also be artificially fabricated either as stacks of uniaxial laminae or using thin‐film technology. Formulations for electromagnetic fields in both classes of chiral media are succinctly presented here.
Circuit Stability
Authors: Svoboda James A.
Published: April 2005

Stability is a property of well‐behaved circuits and systems. Typically, stability is discussed in terms of feedback systems. Well‐established techniques, such as Nyquist plots, Bode diagrams, and root locus plots, are available for studying the stability of feedback systems. Electric circuits can be represented as feedback systems. Nyquist plots, Bode diagrams, and root locus plots can then be used to study the stability of electric circuits.
Circuit Tuning
Authors: Schaumann Rolf
Published: April 2005

Circuit tuningrefers to the process of adjusting the values of electronic components in a circuit to ensure that the fabricated or manufactured circuit performs to specifications. In digital circuits, where signals are switched functions in the time domain and correct operation depends largely on the active devices switching all the way between theirONandOFFstates, tuning in the sense discussed in this article is rarely necessary. In analog continuous‐time circuits, however, signals are continuous functions of time and frequency so that circuit performance depends critically on the component values. Consequently, in all except the most undemanding applications with wide tolerances, correct circuit operation almost always requires some form of tuning.
Coaxial Lines And Waveguides
Authors: Karmakar Nemai Chandra , Padhi Shantanu Kumar
Published: April 2005

In this article we first describe the classical theory in which transmission lines are assumed to be a distributed section of series resistance and inductance, as well as shunt capacitance and conductance. This model is then evolved into the telegrapher equation, which explains the wave nature of electromagnetic energy guided by a two‐conductor transmission line. Finally, the field theory of transmission lines is used to derive coaxial transmission‐line theory.
Combline Filters
Authors: Wang Chi
Published: April 2005

The combline filter, which was first introduced by Matthaei in 1963, is one of the most commonly used bandpass filters in many communication systems and other microwave applications. With modern filter synthesis theory, combline filters having elliptic function frequency responses can be realized by using the nonadjacent couplings. In this article, the lumped‐element lowpass filter prototype is first presented. The equations for conversion between the lowpass prototypegvalues and the impedance/admittance inverters or coupling matrix elements are given. Matthaei's approximated design equations and procedures using Getsinger's design data for rectangular bars, and Cristal's design curves for cylindrical rods are described for design of direct‐coupled combline filters with narrow to moderate bandwidth. A compact tapped‐line input/output coupling configuration is addressed. The general filter topologies are then discussed. The commonly used cascaded triplet and cascaded quadruplet sections for creating more complicated filter structures are presented. Typical combline applications, including multiplexers, dielectric‐filled miniature combline filters, and linear phase or delay filters are presented.
Coplanar Stripline (CPS) Components
Authors: Suh Young-Ho
Published: April 2005

Coplanar stripline (CPS) is a balanced uniplanar transmission line, consisting of two metallic conductor strips separated by a certain gap width, on a substrate. Conventional CPS does not provide bottom metallization of the substrate for ground; instead, one of the conductor strips provides electric ground of the other signal strip.

This article investigates (1) CPS transmission‐line characteristics for practical circuit design and analysis using closed‐form equations; (2) CPS circuit components such as resonators, filters, and “tee” junctions; and (3) applications to antennas and wireless power transmission.

Various new CPS resonators are modeled and designed and their performance investigated in terms ofQfactor or bandwidth. As applications of the proposed CPS resonators, new CPS bandpass filters are demonstrated. The design methods of bandpass filters and their lumped‐element equivalent circuits are presented. A simple CPS lowpass filter is developed using interdigital capacitors and a CPS transmission line.

For CPS component measurements, two types of broadband CPS‐to‐microstrip transition are introduced. Printed dipole antenna feeding can also be easily implemented using this transition.

A novel CPS tee junction using coupled CPS (CCPS) is introduced. As an application of CPS tee junction, a twin‐dipole antenna fed by microstrip‐to‐CPS tee junction is presented at Ka band. A 1×8 printed dipole phased array is developed with the twin‐dipole antenna.

Finally, as a circuit application of CPS, a dual‐frequency rectenna is developed at 2.45 and 5.8 GHz. For dual‐frequency rectenna components, a dual‐frequency antenna, CPS lowpass filter, and CPS bandstop filters are developed. To achieve high RF ‐to‐DC conversion efficiencies at both frequencies, diode analyses are performed for frequency‐insensitive high conversion efficiency.
Coplanar Stripline Transitions
Authors: Simons Rainee N.
Published: April 2005

RF and microwave circuit components can be realized with input/output ports using either balanced or unbalanced planar transmission lines. Interconnections between these components will require a balun or a transition to transform an unbalanced port to a balanced port. This article presents several baluns or transitions, that are of either the Marchand or double‐Y type.
Coupled Transmission Lines
Authors: Paul Clayton R.
Published: April 2005

Two transmission lines whose electromagnetic fields are coupled induce signals from one line into another. This coupling is either intentional as in directional couplers or unintentional, producing unwanted responses in the other line, which is referred to as crosstalk. This discussion of coupled transmission lines will concentrate on the analysis of coupled lines and can be used to design intentional coupling or to assess unintentional coupling as in crosstalk.
Dielectric Measurement
Authors: Bartnikas R.
Published: April 2005

Dielectric measurements are concerned with the characterization of solid, liquid, and gaseous insulating materials over a wide range of DC and AC conditions at different frequencies temperatures, field strengths, and pressures, under differing environments.

Space does not permit a detailed description of all the dielectric measurement procedures and, consequently, only a cursory presentation is made.

Accordingly, the presentation is necessarily confined to a concise description of the most common methods of dielectric measurement employed currently.
Dielectric Resonators
Authors: Weily Andrew R. , Esselle Karu P. , Mohan Ananda Sanagavarapu
Published: April 2005

Dielectric resonators (DRs) are versatile components that have applications in microwave filters, oscillators, antennas, and measurement techniques. They have the advantages of highQfactor, low cost, and excellent temperature stability, and enable significant miniaturization of microwave circuits. This article provides background information on the evolution and theoretical analysis of DRs while highlighting current developments in the field. Mode classifications and field distributions are discussed for lower‐order modes of cylindrical DRs, and mode charts are presented to illustrate the effect of DR aspect ratio and cavity enclosure on the mode spectrum. A simplified analysis method for calculating the resonant frequency of the TE01δmode, the one most commonly used in practice, is described in detail. Information on calculating theQfactor, the temperature coefficient, and details of typical material parameters available from manufacturers are also presented. The article concludes with information on external and interresonator coupling for DR s and methods to compute coupling factors.
Digital Microwave Receivers
Authors: Luy Johann F. , Mueller TH.
Published: April 2005

Reducing complexity in RF systems is a challenge. Research for new broadband and multistandard antennas, high‐frequency bus concepts, and software‐configurable hardware platforms in order to fulfill the needs caused by an increasing number of communication and navigation standards are ongoing tasks.

The high‐speed building blocks of software‐configurable digital receivers are composed of lowpass or bandpass filters, sampling and analog‐to‐digital converter (ADC) circuits, and decimator functions that convert the high‐speed sampling rates into lower rates and higher resolution, respectively. The specific design of receiver hardware architecture is a compromise between the specifications of the services to be handled by the receiver and the availability of components.

The concept of bandpass‐limited subsampling (i.e., where the sampling frequency is lower than the carrier frequency) has become a very appropriate architectural approach as increasing cutoff frequency and speed of semiconductor technologies can be traded against resolution in this concept.

Direct sampling poses high requirements for the analog‐to‐digital converter (ADC). The requirements are reduced significantly if a six‐port digital receiver architecture is used. The functional principle of six‐port devices is based on the measurement of four independent output powers corresponding to the complex ratio between two superposed electromagnetic waves under different phase angles. The six‐port architecture can work under broadband conditions but may be disadvantageous compared to direct‐sampling receivers with respect to their dynamic properties.

Antialiasing filters are necessary components in ADCs. Three‐dimensional micromachined filter structures can provide high quality factors and low insertion losses at microwave and millimeter‐wave frequencies. Transimpedance amplifiers for a bandpass‐limited subsampling approach and limiting amplifiers can be designed and realized in commercial SiGe technology. The sampling circuit itself may use high‐speed Schottky diodes. Using these technologies, digital receivers are now approaching the millimeter‐wave range.
Digital Radio
Authors: Aalo Valentine A.
Published: April 2005

This article presents an overview of digital radiocommunications with emphasis on wireless personal communications.

The main objective of wireless personal communication is to allow the user access to the capabilities of the global network at any time and without regards to location and mobility.

Digital radio, used extensively in second‐generation and the evolving third‐generation systems, considerably improves the quality of the cellular system and enhances the services available to the mobile subscribers.
A/D and D/A Conversion Architectures and Techniques
Authors: Sonkusale Sameer , Zourntos Takis
Published: April 2005

This article is concerned with the data conversion subsystem that interfaces the front‐end and back‐end portions of the transceiver core. A data converter translates signals between analog and digital representations. Our emphasis is on data converters for mobile communication systems in which cost and power savings are a priority. Therefore, although much of our discussion is of a general nature, our presentation is geared toward CMOS integrated circuit implementation and applications with low to moderate bandwidths (e.g., communications with WCDMA, IEEE 802.11a/b, or Bluetooth protocols).
Diodes
Authors: Misiakos Konstantinos
Published: April 2005

In electronics terminology, diode refers to a two‐terminal device that allows current to flow in one direction while it blocks the flow of current in the opposite direction. Such devices usually employ semiconductor junctions or metalsemiconductor junctions. There are also diodes made of vacuum tubes or metalpurely ionic crystal contacts. This article deals with semiconductor p‐n‐junction diodes because they are the most widely used in practice because of their versatility, reproducibility, stability, and compatibility with integrated circuit technology.
Directive antennas
Authors: Alexeff Igor , Rader Mark , Kang Weng Lock
Published: April 2005

Radio antennas that are directive have many advantages over stationary antennas. They can observe in one direction while ignoring much larger signals coming in from the sides. In addition, as transmitting antennas, they can direct a small amount of radiation directly to the proper receiver. Conventional directive antennas use large mirrors for short waves, such as are used in radar. For longerwave antennas, they use reflector and director elements aligned with the antenna. The basic problem with such arrays is that they are mechanically steered, which is slow and difficult to do with large antennas, especially in the presence of wind, ice, or snow.
Distributed Amplifiers
Authors: Koryu Ishii T.
Published: April 2005

The objective of this article is to present various aspects of distributed amplifiers. Distributed amplifiers are by definition, electronic amplifiers consisting of distributed circuit parameters. However, in practice, amplifier systems that consist of a number of discrete amplifiers associated with distributed parameter circuits are often termed distributed amplifiers; this latter amplifier is actually a pseudodistributed amplifier.
Electromagnetic Compatibility
Authors: Paul Clayton R.
Published: April 2005

This article includes general discussion of the subject of designing electronic systems to render them electromagnetically compatible with their environment, to ensure that, they (1) will not cause interference with other electronic systems, (2) be interfered with by other electronic systems, and (3) interfere with themselves. The discussions cover digital signal spectra, nonideal behavior of components, conducted emissions, radiated emissions, crosstalk, and shielding. The subject of governmental regulations is also discussed.
Electromagnetic Materials
Authors: Choudhury P. K. , Singh O. N.
Published: April 2005

This article describes the electromagnetic properties of the medium or material in which the process of electromagnetics takes place. The introductory part discusses the evolution of electromagnetics based on theories and experiments by the pioneering scientists. The following portions of the article deal with the different types of materials, including isotropic dielectrics, conductors, semiconductors, superconductors, anisotropic dielectrics, and electrooptic materials. The fundamentals of magnetic materials are described in slightly greater detail, explaining the mechanisms of magnetization and special materials such as ferrites. Bianisotropic materials and their constitutive equations are also discussed. Here the focus is on some of the fundamental aspects of the constitutive characterization of bianisotropic media. The last two sections describe the basics and important applications of the phenomena of magnetostriction and piezoelectricity.
Electromagnetic Shielding
Authors: Celozzi Salvatore , Araneo Rodolfo
Published: April 2005

Electromagnetic shielding is an important constraint in the design of RF and microwave devices consisting in the mitigation of the emission levels of electromagnetic (EM) sources and/or in the protection of people or electrical and electronics apparatus and systems against possible effects due to external EM fields. Very often the need for electromagnetic shielding depends not only on functioning motivations but also on the compliance with standards fixing the limits of emission or immunity for various classes of apparatus and systems. Shielding theory, including analytical formulations, has been well developed in order to obtain guidance in practical problems and to firmly grasp the key factors on which the theory of electromagnetic shielding is based. For the difficulty in handling real configurations by means of exact analytical expressions, approximate formulations have been developed and improved over the years, while the analysis of the shielding effectiveness of closed structures, often referred to as enclosures, is generally performed in either the frequency or time domain, by using numerical techniques.
Electromagnetic Subsurface Remote Sensing
Authors: Chen S. Y. , Chew W. C.
Published: April 2005

Subsurface electromagnetic (EM) methods are applied to obtain underground information that is not available from surface observations. Subsurface EM methods include a variety of techniques depending on the application, surveying method, system, and interpretation procedure, and thus a “best” method simply does not exist. One of the most challenging parts of subsurface EM methods is interpretation of the data. Data interpretation is also a critical factor in evaluating the effectiveness of the system. In the following sections, we will use several typical applications to outline the basic principles of subsurface EM methods. Physical insight is emphasized rather than rigorous mathematical analysis.
Electromagnetics, Time‐Domain
Authors: Bushyager Nathan A. , Tentzeris Manos M.
Published: April 2005

In this article, various time‐domain electromagnetic simulation methods, including the finite‐difference time‐domain (FDTD), transmission‐line matrix (TLM), finite‐element time‐domain (FETD), and multiresolution time‐domain (MRTD) techniques are discussed in detail along with grid optimization approaches. In addition, conformal meshing techniques, specifically finite‐volume time‐domain (FVTD) and generalized Yee FDTD methods are briefly descirbed. Also included is a discussion of code parallelization, grid excitation, absorbing boundary conditions, antenna modeling, and methods that can be used to deriveSparameters from time‐domain output data.
Electronic Warfare
Authors: Spezio Anthony E. , Duckworth Alan N. , Klemm Francis J. , Moroz Stanley A. , Talley James M.
Published: April 2005

Electronic warfare (EW) is the systems discipline that exploits an adversary's use of the electromagnetic spectrum to overcome threats that use communications, navigation, and radar systems. This article includes a description of the EW timeline and the various phases of conflict. Also provided is a summary description of the signal environment in which EW systems operate.

This article includes a description of the EW timeline and the various phases of conflict. Also provided is a summary description of the signal environment in which EW systems operate.
Fabry–Perot Resonators
Authors: Sauleau Ronan
Published: April 2005

The characteristics and the main applications of Fabry–Perot (FP) resonators are described at microwave frequencies, referring to a well‐documented state of the art.

This article is organized in three sections. In the first, we present the basic properties of plane‐parallel FP interferometers using the traditional ray approach. Their performance is defined mainly in terms of power reflectivity of both partially transparent mirrors. Nevertheless many microwave and millimeter‐wave FP cavities employ metallic strip gratings or meshes as reflecting parts. The impact of the dispersive characteristics of these mirrors is investigated in details in Section 2. For that purpose, we first study the scattering parameters of inductive and capacitive meshes using transmission‐line models and compare them to rigorous numerical results. Then we analyze the influence of the grid geometries on the performance of plane‐parallel FP cavities (frequency responses, resonant frequencies, half‐power bandwidth, and insertion loss). Finally design rules and multilayer FP structures with metallic or dielectric mirrors are briefly considered. Various applications are discussed in Section 3: (1) frequency filters and diplexers, (2) directive antennas and multibeam and frequency beam scanning antennas, (3) open resonators with spherical mirrors for dielectric measurement, and (4) quasioptical power combiners and oscillators.
Signal Fading in Radio Communications
Authors: Janaswamy Ramakrishna
Published: April 2005

In this article we describe the causes of signal fluctuation in wireless systems and describe the phenomena of short‐term and long‐term fading. Some of the topics included are narrowband and wideband fading, Rayleigh fading, Ricean fading, lognormal fading, level crossing rates, average fade duration, channel coherence time, Doppler spread, delay spread, and coherence bandwidth. The impact of fading on the performance of systems and in the design of cell size is discussed.
Feedback Amplifiers
Authors: Schubert Thomas F.
Published: April 2005

This article considers the benefits of negative feedback on amplifier design: stabilization of gain, reduction of nonlinear distortion, increased bandwidth, and selective modification of input and output resistance. Basic definitions are followed by a general discussion of the properties of a feedback system. Amplifiers are divided into four categories of feedback topology, and the specific properties of each topological type are determined. The drawbacks of feedback, reduction of gain, and the possibility of oscillation are also considered. Several compensation methods to improve amplifier stability are discussed.
Ferrite Phase Shifters
Authors: Hord William E.
Published: April 2005

Phase shifters are used extensively in the microwave and millimeter‐wave region primarily as array elements in phased‐array antennas.

The article describes the evolution of ferrite phase shifters that have made the transition from the research laboratory to the production floor. Wherever possible, the author has identified the systems that use a specific type device.
Filter Synthesis
Authors: Lueder Ernst
Published: April 2005

The most common types of components for classical filters are lossless inductors and capacitors, as well as ideal transformers for the two‐port and resistances R1 and R2 as internal resistance of the source and as the terminating load. This case is treated in this article. Other types of components are switches such as FETs, capacitors, and operational amplifiers in so‐called switched capacitor filters or delays, adders and multipliers in digital filters or resistors, capacitors and operational amplifiers in RC‐active filters, or electromechanical transducers and a set of electrodes in surface acoustic wave (SAW) filters, which are treated in the last section.

Guidelines will be presented on how to determine from filter tables the component values of a filter meeting given specifications. This should enable a system engineer to achieve a quick filter design by selecting the appropriate type of filter and by then finding the component values in a table.
Finline Components
Authors: Menzel Wolfgang S.
Published: April 2005

Finline is a planar transmission line suspended in theEplane of a metal waveguide. The electromagnetic field is guided by a slot in the finline metallization. This contribution gives an overview of the possibilities of realizing passive as well as active components based on this type of transmission line. The article begins with a discussion of filters, directional couplers, and antennas and nonreciprocal components are mentioned later. It continues with a discussion of diode‐based components such as detectors, p‐i‐n diode attenuators or switches, mixers, and phase shifters. After a short remark on oscillators and amplifiers, a number of integrated components and front ends are presented.
Frequency‐Division Multiplexers
Authors: Snyder Richard V.
Published: April 2005

Frequency‐division multiplexers are networks used either to split an input spectrum into possibly, but not necessarily, contiguous subportions, or alternatively to combine discrete spectral inputs into a common output. Designers and theoreticians have traditionally treated the design methodology as “black art,” and it has been difficult to formally learn “how to multiplex.” This article presents some of the many multiplexing techniques that have been developed since the early 1950s, and provides a good starting point for would‐be multiplexer designers.
Frequency Independent Antennas
Authors: Filipovic Dejan S. , Cencich Thomas P. , Nurnberger Michael W.
Published: April 2005

Frequency‐independent (FI) antennas are radiating structures capable of maintaining consistent impedance and pattern characteristics over multiple‐decade bandwidths. Their finite size limits the lowest frequency of operation, and the finite precision of the center region bounds the highest frequency of operation. The geometry of a frequency‐independent antenna must be specified by angles alone, and principles such as truncation and self‐complementarity are necessary and desired, respectively. In this article, Rumsey's theory of FI antennas, developed in the mid‐1950s, is thoroughly discussed, and historical highlights listing the most important contributions in this area are given. A mathematical derivation for a general FI structure is provided, and some special cases are considered both theoretically and practically. A description and an explanation of the underlying theory of operation for several FI antenna types, including equiangular spirals, conventional and unconventional sinuous antennas, and log‐periodic folded slot arrays, are also provided. A view of frequency independence through the modal content and contamination of the radiated far field is emphasized. Considerations for flush/conformal mounting are briefly discussed, including the use of log‐periodic lossless cavities and broadband conical cavities.
Galerkin Method (Rayleigh–Ritz Method)
Authors: Weile Daniel S. , Wildman Raymond A. , Pisharody Greeshma , Mohan Anuraag
Published: April 2005

Galerkin's method and the Rayleigh–Ritz method form the mathematical underpinnings of many modern computational techniques for the solution of electromagnetics problems. In this work, the history of these two methods is reviewed, and each of the methods is described in detail. The relationship between the methods is explored, as is their relationship with the modern finite‐element method and method of moments. Numerical examples of the methods are provided to clarify the exposition.
Gallium Arsenide Technology and Applications
Authors: Manes G. F.
Published: April 2005

Starting from the early 1970s, the increasing request for solid‐state devices operating at microwave frequencies lead to investigations of semiconductor structures as alternatives to silicon.

Among various solutions, gallium arsenide generated interest and eventually emerged as the favorite material for high‐frequency applications due to the high carrier mobility compared with silicon devices.

The advantages in speed and high‐frequency performance of GaAs are slightly offset by the manufacturing process limitations of GaAs, in terms of both complexity and reproducibility as opposed to Si.

GaAs devices find application at RF and microwave frequencies for both linear and high‐speed logic applications.

GaAs microwave devices find extensive use in consumer applications as well in sophisticated warfare electronics. GaAs devices are used in the form of discrete components or microwave monolithic integrated circuits (MMICs). GaAs also exhibits relevant optical properties and finds extensive applications in optoelectronics, including LEDs, laser diodes, and solar cells.
Uniform Geometrical Theory of Diffraction
Authors: Pathak Prabhakar H.
Published: April 2005

Keller's geometrical theory of diffraction (GTD) [1,2] constitutes a major breakthrough for solving problems of electromagnetic (EM) radiation and scattering at high frequencies. The GTD can also be applied to solving acoustic and elastic wave problems; however, only the EM case is discussed here.

Recently, the development of fast solvers for signifi‐cantly increasing the efficiency of numerical methods in solving large problems has met with some success. However, for truly large problems, asymptotic high‐frequency methods in general, and especially ray methods such as the GTD and its uniform version, still remain the most useful analysis tools.
Ge‐Si Alloys and Devices
Authors: Russer Peter , Luy Johann-Friedrich
Published: April 2005

The silicon–germanium heterojunction bipolar transistor enabled the breakthrough of siliconbased MMIC (monolithic millimeter‐wave integrated circuit) technology [1,6]. Amplifiers and tunable oscillators or with maximum operation frequencies beyond 80GHz become feasible.

Silicon as a substrate for millimeter‐wave monolithically integrated circuits was suggested in 1981 by RCA [22]. Since 1986 in the field of silicon monolithic millimeter‐wave integrated circuits (SIMMWICs) there have been research activities at the former AEG‐Telefunken Research Institute (now DaimlerChrysler Research Center) and at the Technische Universitat¨ München [23–29].

Monolithic integrated millimeterwave circuits based on silicon and SiGe will give new options for millimeter‐wave sensor and communication applications.