bluuebunny/crossref_metadata_2025 huggingface dataset:
Skin Effect
Authors: Olyslager Frank , de Zutter Daniël
Published: April 2005

The skin effect is the property that electromagnetic waves penetrate only a small distance into a conductor. The fields and induced currents decay exponentially with the distance from the surface. The distance over which the fields and induced currents decrease by a factor ofeis the skin depth. The ratio of the voltage drop along the surface of the conductor to the current flowing in the conductor and causing this voltage drop is the surface impedance. Expressions for the skin depth and the surface impedance are in the first instance derived for a plane conductor interface. The results for a plane conductor are also applicable for a curved conductor as long as the radius of curvature is large compared to the wavelength. For a conductor with a finite thickness an expression for the surface impedance is derived that takes into account the finite thickness of the conductor. The roughness of the conductor surface increases the surface resistance. This increase is quantified by an empirical law. The concept of the surface impedance allows an efficient inclusion of conductors with finite conductivity in numerical electromagnetic simulation techniques such as integral equation techniques, finite‐element techniques, and finite‐difference time‐domain techniques.
Sky Wave Propagation at Medium and High Frequencies
Authors: Davies Kenneth
Published: April 2005

In this article, we shall discuss the following topics: 1. Basic physical properties of sky wave propagation (namely, refraction, reflection, penetration, and absorption) 2. relationships between vertical propagation and oblique propagation 3. ionospheric models 4. characteristics of medium frequencies 5. characteristics of high frequencies 6. prediction programs for ionospheric sky wave performance 7. real‐time channel evaluation
Slot Antennas
Authors: Nakano Hisamatsu
Published: April 2005

The radiation pattern and conductance of a thin straight half‐wavelength slot are derived using an assumed electric field distribution over the slot. Subsequently, Babinet's principle, which provides a relationship between the input impedances of a slot and a conducting plate, both having the same shape, is derived. In addition, an antenna evaluation method based on the finite‐difference time‐domain method is briefly described. Using the finite‐difference time‐domain method, straight, bowtie, loop, curl, and spiral slot antennas are analyzed. The analysis reveals (1) the effects of the finiteness of the conducting sheet, in which the straight slot is cut, on the radiation characteristics; (2) the effects of the bowtie angle on the radiation characteristics; (3) the input impedance of the loop as a function of the circumference; and (4) the frequency responses of the curl and spiral slots, acting as circularly polarized radiation elements.
Spaceborne Radar
Authors: Kwok Ronald , Yueh Simon H. , Fu Lee-Lueng
Published: April 2005

Here, we review three different applications of active microwave remote sensing that have contributed geophysical measurements on a scale and accuracy that surpass what could be accomplished with airborne or in situ observations. These are synthetic aperture radar interferometry, scatterometry, and altimetry. For each of these areas, we describe the measurement principle, the current technology, the applications, and give a brief look into the future.
Spiral Antennas
Authors: Cencich Thomas P. , Filipovic Dejan S.
Published: April 2005

Spiral antennas were introduced in the mid‐1950s. They were the first antennas to exhibit uniform impedance and pattern performance over multioctave bandwidths. Spirals were the cornerstone and mathematical quintessence of a new concept in antenna theory termedfrequency-independent antennas. In this article, various aspects related to the analysis and design of spiral antennas are discussed. The theory of spiral operation, often referred to asband theory, is discussed. Also included are characteristic geometries and shapes including equiangular and Archimedian planar and conical spirals. Theoretical and practical aspects needed for successful design and understanding of spiral antennas are reviewed. Special attention is given to understanding the modal performance of multiarm spiral antennas and its importance to overall antenna characteristics, analysis theory, mode‐forming networks, multimode excitations, and similar. Various feeding methods including infinite and tapered baluns, as well as coaxial bundles are described. Dual‐polarized spiral designs including inside/outside‐fed spirals and modulated armwidth (MAW ) spirals, and bandwidths of various spiral geometries are discussed. The article also includes some aspects of spiral miniaturization; discussions of challenges of nondissipative cavity backing, utilization of spirals as reflector feeds, the modal decomposition technique; and an overview of numerical methods utilized for successful design of spiral antennas. The article is organized in several sections, each devoted to a separate topic, with illustrations and tables utilized for further clarification and demonstration of discussed concepts.
Squid
s
Authors: Fagaly Robert L.
Published: April 2005

SQUID instruments consist of a SQUID amplifier or sensor and a detection circuit that transforms the signal of interest into a magnetic flux that is detected by the SQUID sensor. Associated control electronics transform this signal into a room temperature voltage that is available for additional signal processing if needed. The SQUID amplifier and the detection coils are superconducting devices. Thus some type of refrigerant (e.g., liquid helium or nitrogen) or refrigeration device is needed to maintain the SQUID (and detection coil) in the superconducting state. Additional signal‐conditioning electronics may be needed to improve the signal‐to‐noise ratio.
Stability of Nonlinear Systems
Authors: Chen Guanrong
Published: April 2005

This article outlines the notion of stability of nonlinear systems, for both continuous‐time and discrete‐time settings. Basic concepts and fundamental theorems of various system stabilities are introduced. These mainly include the important Lyapunov stability theory, along with some others such as the Zhukovskij stability theory and orbital as well as structural stabilities. Bounded‐input bounded‐output stability of maps is also discussed.
Stripline Components
Authors: Barrio-Garrido R. M. , Salazar-Palma M. , Sarkar T. K. , Adve R. S.
Published: April 2005

The fast spread of wireless and high‐speed communications brings the need for providing inexpensive and compact microwave circuits at very high frequencies. A promising approach is the development of the modern multilevel or three‐dimensional monolithic microwave integrated circuits (MMIC), printed circuit boards (PCB), and the new technologies for integration of millimeter‐wave systems like low‐temperature cofire ceramics (LTCC). In such environments, stripline‐like components play a key role and focus a great interest nowadays, because multilayer, embedded transmission line (ETL) based on stripline configurations originates from the three‐dimensional packages. Moreover, stripline is one of the preferred transmission lines in most of this environments because, among other advantages, radiation and dispersion are negligible and ground planes provide effective shielding. For example, in antenna feeding, stripline has probed to be a compact and effective solution. In filter applications, suspended striplines are extensively used by engineers because of their low unloaded Q‐factor. However, the multiconductor and multilayer structures present some complications derived from the shorting posts or via holes, spurious modes that result in crosstalk and losses, complex geometries, and so on. In many cases, it is necessary to find new design solutions to avoid parallel‐plate mode coupling, but full‐wave analysis becomes a complicated task. In this article, these issues are exposed, and both classic stripline components and new multilayer structures are presented. We discuss some design considerations, advantages and drawbacks, classic and new devices, and modern solutions recently reported for old and new necessities of the design and analysis of stripline configurations.
Superconducting Cavity Resonators
Authors: Padamsee Hasan
Published: April 2005

A key component of the modern particle accelerator is the device that imparts energy to the charged particles. This is an electromagnetic radio frequency (RF) cavity resonating at microwave frequencies typically between 50MHz and 3000 MHz. Superconducting cavities economically provide high CW operating fields. Another benefit is that superconducting cavities can be designed to have a large beam aperture that reduces the beam cavity interactions, allowing higher beam quality and higher beam current. There are two distinct types of superconducting cavities, depending on the velocity of the particles. The first category is for accelerating charged particles that move at nearly the speed of light, such as electrons in a high‐energy linear accelerator [e.g., at TJNAF at Jefferson Lab in Newport News, VA] or a storage ring [e.g., LEP at CERN in Switzerland]. The second type is for particles that move at a small fraction (e.g., 0.01 to 0.3) of the speed of light, such as the heavy ions emerging from a dc highvoltage Van de Graaff accelerator.
Superconducting Filters and Passive Components
Authors: O’Callaghan Juan M. , Collado Carlos , Talisa Salvador H. , Mateu Jordi
Published: April 2005

This article gives an overview of the applications of high‐temperature superconductors for passive microwave devices, with an emphasis on planar filters. It includes a description of the basic characteristics of these superconducting materials and relates these characteristics to device performance. In the case of filters, the low loss of superconducting films allows the development of small, planar filters with superior performance. One important application of these filters is preselector filters for receiver front‐ends, because they combine high‐frequency selectivity with low insertion loss and low noise figure because of the low temperatures of operation.

The article also gives a short overview of applications of high‐temperature superconducting materials in planar delay lines, cryocoolers, and cryogenic packaging.
Superconducting Microwave Technology
Authors: Choudhury Durga P. , Sridhar S.
Published: April 2005

Superconductivity is a remarkable state of matter in which electric current can flow inside materials without any detectable resistance. In a superconductor, perfect electric conductivity or zero resistivity occurs only below a “critical temperature”TC. A direct current induced in a superconducting ring has been shown to persist for over 2 years without any measurable decay. Another important characteristic of superconductors was the discovery by W. Meissner and R. Ochsenfeld in 1933 that a superconductor expels all magnetic flux from its interior; that is, a superconductor is also a perfect diamagnet. A key area of technological applications of superconductors is in high‐frequency devices, particularly at frequencies in the radiowave, microwave, and millimeterwave spectral ranges.
Surface Acoustic Wave Devices
Authors: Morgan D. P.
Published: April 2005

A surface‐acoustic‐wave (SAW) device employs an acoustic wave guided along the surface of a piezoelectric crystal, in which the stresses and strains of the wave are coupled to electric fields. The wave has a low velocity, typically 3500 m/s, and propagates with low attenuation. These features enable compact low‐loss devices to be developed for electronics applications at frequencies up to several gigahertz. Arrays of metal electrodes are used to generate, detect, or reflect the waves. This technology has enormous versatility because standard lithographic techniques can be used to fabricate almost arbitrary geometries.

This article summarizes the nature of surface waves and some relevant propagation effects, including diffraction. The interdigital transducer, used in all these devices for wave generation, is described. A survey of suitable materials is given, including quartz, lithium niobate, and lithium tantalate. Transversal bandpass filters are weighted using apodisation or withdrawal weighting. They are widely used in TV receivers, as well as in professional equipment which calls for very high‐performance devices. For radar, SAW pulse compression filters perform a correlation operation, increasing the range capability. Other devices perform correlation for spread‐spectrum communication waveforms; an example is the SAW nonlinear convolver, which is capable of instantaneous programmability. For mobile telephony there has been a strong demand for miniature low‐loss bandpass filters, and a wide variety of novel SAW devices have been developed. For example, impedance element filters give 1 dB loss at 900 MHz, with 30 MHz bandwidth and a package size of 2×2 mm2. For IF CDMA filters, a modified form of the transversal filter, called the R‐SPUDT (resonant single‐phase unidirectional transducer), enables both low loss and small size to be obtained. For GSM IF circuits, transverse‐coupled resonator filters have been developed to give a very narrow bandwidth of 200 kHz.

The article concludes with a superficial survey of the theory of these devices.
Surface Mount Technology
Authors: Trybula Walter J. , Trybula Michael
Published: April 2005

Surface mount assembly (SMA) is the description of a technology that incorporates the electrical and mechanical of components to printed wiring boards (PWBs) or a similar type of circuit substrate. The term
surface mount
comes from the methodology of attaching the components.

Many categories of packages can be employed in surface mount assembly. They can be identified into two categories: leadless devices and leaded chip carriers.
Electromagnetic Surface Waves
Authors: Wu Zhipeng
Published: April 2005

In this article, the electromagnetic surface waves propagating along an interface between two dielectric media or an interface between air and a multilayered structure in planar, cylindrical, and spherical geometries are introduced. Specific surface waves considered are (1) the Zenneck surface wave, (2) the surface wave on a conductor‐backed dielectric slab, (3) the radial cylindrical surface wave on a flat surface, (4) the axial cylindrical surface wave, (5) the surface wave on a dielectric‐coated conducting cylindrical, (6) Norton and trapped surface waves on flat ground interface, (7) surface‐wave propagation over an inhomogeneous flat surface, and (8) surface‐wave propagation over a spherical ground. Several examples are given to illustrate the propagation of surface waves in these geometric structures. The surface waves propagating along Earth's surface have been used for wireless communications and remote sensing. On the other hand, the surface waves on conductor‐backed dielectric slabs become a problem in microwave printed circuits and microstrip antenna systems. The understanding and control of surface waves are therefore important in radio systems.
Telemedicine
Authors: Chen Chang Wen
Published: April 2005

Telemedicine—which combines many innovative information technologies that integrate research areas in human—computer interaction, data storage, processing, and compression with communications networking to improve healthcare—has been recognized as a way to provide an effective and versatile solution to many of the intransigent problems in healthcare delivery.
Television and FM Broadcasting Antennas
Authors: Bendov O.
Published: April 2005

Antennas for television and FM broadcasting are usually installed on tall towers to maximize the service area. A high‐power transmitter feeds the broadcast antenna to provide “passable” picture and sound at distances approaching 70 m. In the UHF range (TV channels 14 to 69), the transmitter's peak power could be as high as 280kW. In the VHF range (TV channels 2 to 13 and FM), a transmitter's peak power of 70kW is not unusual. In addition to high power‐handling capability, broadcast antennas must continue to perform under severe weather conditions, such as ice storms and hurricane winds. Antennas, especially for television broadcasting, must be designed to accept and radiate all of the power delivered by the transmitter. Antennas for digital television must be designed to meet more stringent specifications than those for antennas for analog television.
Television Antennas
Authors: Kawakami Haruo
Published: April 2005

In this article, various types of modified batwing antennas are analyzed theoretically with the aid of the moment method. Results are compared with measurements to examine detailed performance of antenna elements, demonstrating the accuracy of the analytic method.
Thermal Analysis and Design of Electronic Systems
Authors: Kraus Allan D. , Bar-Cohen Avram , Geisler Karl J.
Published: April 2005

The challenges posed by high chip heat fluxes and ever more stringent performance and reliability constraints make thermal management a key enabling technology in the development of microelectronic systems for the twenty‐first century. Thus, thermal packaging efforts must be performed in the context of the salient trends and parameters that characterize the IC technology and the electronic products industry.

Recent road‐mapping efforts, have affirmed the expectation that improvements in CMOS semiconductor technology will continue unabated into the early part of the twenty‐first century. Exploiting the potential of this IC technology, with the attendant increase in chip size, switching speed, and transistor density, will necessitate significant improvements in packaging technology.
Thin Films
Authors: Wasa Kiyotaka , Setsune Kentaro
Published: April 2005

Thin film ferroelectric materials and hexagonal piezoelectric materials are essential for fabrication of electronic and/or photonic devices. Ferroelectric materials are dielectrics that have a spontaneous polarization with nonlinear hysteretic properties and show several unique properties including high dielectric permittivity, high piezoelectricity, high pyroelectricity, and high electrooptic characteristics. Thin film ferroelectric materials have a high potential for miniaturization and/or integration with the semiconductive devices. Thin films are also important to the understanding of ferroelectricity. Thin films are commonly fabricated by depositing individual atoms on a substrate. The film thickness is typically less than several micrometers.
Thin Film Resistors
Authors: Collins F. M. , Anderson W. A. , Ma E. M.
Published: April 2005

In this article, we will discuss the historical background and technological evolution of thin film resistors. We will also review resistor technology design concepts, including requirements for (1) the range of resistance values, (2) their precision, and (3) the physical size in terms of power or voltage demands, materials used in production, finished formats, performance characteristics, and some advantages of integrated thin film resistor production.
Transient Analysis
Authors: Feely Orla , Mulkeen Brian
Published: April 2005

This article reviews the basic principles of transient circuit analysis, which is a long‐established branch of circuit theory with a wide range of applications. It examines transient behavior in linear circuits and explains the type of behavior that can occur in these circuits. It shows how this behavior can be analysed by solving appropriate differential equations, or by applying the Laplace or Fourier transform. Application of the Laplace transform to distributed circuits is also considered.
Transmission Lines and Parameters
Authors: Chen Ji , Chen Richard L.
Published: April 2005

Transmission lines are defined as waveguiding structures that can support transverse electromagnetic (TEM) waves or quasi‐TEM waves. This article concentrates on five commonly used transmission‐line structures. The transmission‐line parameters are first introduced in the derivation of the telegrapher's equations by dividing the transmission line into electrically small segments that can be described by the lumped‐element circuit theory. The transmission‐line parameters are then derived from rigorous electromagnetic field analysis. Five commonly used transmission lines—parallel‐plate waveguides, coaxial cables, two‐wire lines, striplines, and microstrip lines—are presented, and the techniques used to extract their corresponding transmission‐line parameters are given. A common integrated circuit (IC)‐level transmission‐line structure is presented, and the challenges in parameter extraction for future micro‐ and nanoscale transmission lines are also discussed.
Traveling Wave Antennas
Authors: Waterhouse Rod B.
Published: April 2005

In this article, a review of common traveling wave antennas is presented. We briefly discuss the structural characteristics, design trends, and overall performance of several traveling wave antennas including Beverage antennas (wire and printed), horn antennas, reflectors, and tapered slots. Some examples of manufactured traveling wave antennas are given. We also attempt to outline the fundamental properties of this general class of antenna and how it can be differentiated from resonant style radiators. It will be shown that traveling wave antennas are essential for a variety of applications ranging from sophisticated radio astronomy platforms to simple low‐frequency communications.
Tunnel Devices
Authors: Sargent Edward H. , Xu J. M.
Published: April 2005

Tunnel devices take advantage of the wave‐like properties of charge carriers in implementing a desired function. The term tunneling refers to the movement of matter from one side of an energetic barrier to the other even though it does not possess sufficient energy to overcome the potential barrier according to the laws of classical mechanics. Instead, the quantum‐mechanical wave function of the particle penetrates inside the barrier and extends into the medium on the far side. Tunnel devices typically possess nonlinear, nonmonotonic current‐voltage characteristics and are characterized by very rapid fundamental propagation times. They find application in such diverse areas as microwave oscillators; multiple‐level logic, switches, memory elements; and lasers.
Variable‐Frequency Oscillators
Authors: Gutierrez Germán
Published: April 2005

Oscillators are abundant around us. Most oscillators are of two basic kinds: sinusoidal and relaxation. This article covers the main topologies for all popular oscillators and the ways to make their frequency of oscillation variable. The description is independent of frequency and can be applied from very‐low‐frequency to microwave oscillators. Mechanical examples give a very simple explanation for the mechanism of oscillators and the concept of resonance.
Very High Frequency Range
Authors: Campbell Richard L.
Published: April 2005

The Very High Frequency (VHF) range extends from 30MHz to 300 MHz, which means that when a VHF sine‐wave signal is observed on an oscilloscope, the trace completes from 30 to 300 million cycles each second. The wavelength and frequency of VHF signals has a profound impact on the hardware we build to use these frequencies. The 30 to 300MHz frequency range has been popular since radio engineers first discovered how to reliably generate and amplify VHF signals during the 1930s. The VHF range has significant advantages for some common applications over higher and lower frequency ranges.
Voltage‐To‐Frequency Converters
Authors: Vidal-VerdÚ Fernando , Navas-GonzÁlez Rafael , Rodriguez-VÁzquez Angel
Published: April 2005

Voltage‐to‐frequency‐converters (VFCs) do typically employ relaxation oscillators to generate an output signal whose frequency depends linearly on an input voltage. VFCs are data converters; they are designed to codify the input voltage by means of the output frequency. Hence, they have strong requirements regarding linearity, dynamic range, and stability. On the other hand, compared to other converters, they have the advantage of low cost, particularly for large resolutions; 13 bit resolution is typical, and more than 20 bits are feasible. However, in such a case several milliseconds may be necessary to complete the conversion—the smaller the resolution, the shorter the conversion time.

The serial frequency modulated output provided by VFCs is particularly well suited for telemetry, to send the outcome of a measurement by wire, radio, or fiberoptic links. After the frequency‐modulated signal is received, it can be easily codified into a digital word, or converted back into a voltage by a frequency‐to‐voltage converter. This type of output simplifies galvanic isolation through the use of either an optocoupler or a magnetic coupler. The serial output is also useful for increasing system compactness if throughput requirements are not high. Although many smart monolithic sensors have serial frequency‐modulated outputs, a VFC is needed in case we have an output voltage like that of a Wheatstone bridge after being amplified by an instrumentation amplifier, or the output of a generating sensor such as a thermocouple.

This article deals first with the concepts behind voltage to frequency conversion, and then describes the main types of VFCs on the market, their limitations and main applications. Frequency‐to‐voltage converters are also briefly described.
Waveguide Discontinuities
Authors: Sorrentino R. , Alimenti F.
Published: April 2005

This article deals with waveguide discontinuities that are unavoidably present in any microwave circuit either unintentionally or to the purpose of performing a prescribed function. After a brief introduction, this contribution illustrates the basic theory behind the modal analysis of such structures and their general properties. Finally a categorization of waveguide discontinuity is proposed with reference to some geometric characteristics that are related to the corresponding electromagnetic problem.
Guided Electromagnetic Waves
Authors: Joines William T.
Published: April 2005

Closed‐form solutions for TEM, TM, and TE waves in guiding structures are obtained from Maxwell's equations. Propagation parameters, frequency ranges, broadbanding techniques, and design examples are presented. Dielectric waveguides for microwave and optical frequencies are also presented.
Wireless Communication Systems
Authors: Armada Ana García , Ramos López Javier , González Serrano Francisco J.
Published: April 2005

This article introduces wireless communications systems and explains the different products and standards related to wireless communications. The article is divided into five main sections.

A brief introduction in Section 1 offers a perspective of the evolution of wireless communications systems and introduces a useful classification. After this introduction, Section 2 is devoted to the explanation of basic concepts and fundamentals of the different wireless products, while Section 3 explains the related technology.

Sections 2 and 3 both make it easy to understand Section 4, in which five wireless products and related standards are detailed: cellular, cordless, trunking, paging, WLAN, and WPAN systems.

Finally, Section 5 offers a brief vision of the future evolution of wireless systems, introducing advanced technologies such as “smart” antennas and spacetime transmission diversity (STTD), and research, towards the fourth generation of mobile communications.
Calibration of a Circular Loop Antenna
Authors: Aykan Aydin
Published: April 2005

The calibration of a measuring loop antenna means assigning an antenna factor
K
for each frequency in the entire measurement band. This factor can be found either by calculating the impedance of the loop or by using a well‐defined standard magnetic field of a transmitting antenna. For both methods, it is necessary to obtain an accurate relation between the magnetic field and the geometric dimensions of the loops. Generally, a manufactured loop has a complex geometric shape with complex electrical behavior so that its impedance cannot be accurately determined analytically. In such cases, the standard magnetic field method remains as the only alternative for calibration. The formulas needed for implementation of the method, which takes into account the dimensions of the loops with finite conductor radii as well as the current distribution along the loop, are given. With the procedure presented here, the calibration is reduced to an accurate measurement of attenuation.
Corrugated Horn Antennas
Authors: Lucci L. , Pelosi G. , Selleri S. , Nesti R.
Published: April 2005

In this work the basic theory of circular corrugated horn antennas is presented, using easy concepts with simple mathematics. The aim is to give the reader an understanding of the fundamental electromagnetic properties of these devices and to provide a set of quantitative design tools for the electromagnetic engineer.

The wave propagation problem in corrugated waveguides is approached by approximating the field boundary conditions on the corrugation limit surface and by making further assumptions, suggested by practical considerations, with a consequent mathematical simplification of the theory. This approach has the major advantage of providing an analytical solution for the electromagnetic field, which is accurate as far as the approximate boundary conditions are valid and that enables us to highlight the most relevant features of corrugated waveguides.

The problem of radiation from corrugated horns is addressed in a similar way by choosing an approximated model sufficiently accurate for almost all practical needs. This model, the “Gaussian beam model,” has a simple analytical formulation and is rigorously treated. The final result of this approach is a set of analytical formulas relating electromagnetic properties to geometric parameters that are very useful in the design.

Then, further design aspects concerning the throat region, the phase center, and cross‐polarization are introduced and a numerical methods for highly accurate analysis of corrugated horns are described, ending with some design examples.
Reconfigurable Antennas
Authors: Bernhard Jennifer T.
Published: April 2005

High‐speed wireless systems of the future will require more functionality from antennas than can be provided by classic designs. One approach to this challenge is to develop reconfigurable antennas. The goal of a reconfigurable antenna—one that can adjust its operating frequency, bandwidth, and/or radiation pattern to accommodate changing system requirements—poses significant challenges to both antenna and systems designers. This article first defines antenna reconfigurability and then highlights some of the more recent advances in the area of antenna reconfiguration. Additionally, some of the barriers that still need to be overcome to arrive at realizable technologies are discussed. These barriers include the development of reliable, mass‐manufacturable radiofrequency microelectromechanical system (RF MEMS) switches, the design of switch bias networks that will not interfere with antenna operation, and the expansion of signal processing and feedback algorithms to fully exploit this new antenna functionality.
Reflectarray Antenna
Authors: Huang John
Published: April 2005

This article gives an overview of the development history and key design methodologies for the reflectarray antenna, in particular the printed reflectarray. A reflectarray is an array antenna similar to a parabolic reflector, but with its reflecting surface capable of being designed either flat or slightly curved. On the reflecting surface, there are many isolated (not physically combined by power division lines) antenna elements, which are illuminated by a feed antenna located at the vicinity of a focal point. These isolated elements are each predesigned with a particular electrical phase delay to compensate for the phase differences due to different pathlengths from the feed. The illuminating electrical field from the feed will then be scattered from these isolated elements and form a cophasal concentrated beam in the far‐field distance.
Multimode Equivalent Network Representations
Authors: Guglielmi Marco
Published: April 2005

The objective of this article is to describe the formulation of multimode equivalent network representations of waveguide junctions. Both planar and arbitrary junctions are discussed, thereby covering essentially all possible cases of engineering interest for microwave and millimeter‐wave applications. The theory presented in this article effectively transforms complex field problems into linear algebraic problems of simple solution. The theory described is rigorous and computationally very efficient and can therefore be used as a very solid theoretical frame for the development of advanced full‐wave electromagnetic simulation computer programs. In addition to theory, a number of applications are also demonstrated showing very good agreement between measured and simulated performances, thereby fully validating the theory presented.
Microwave Detectors
Authors: Ham Ronald E.
Published: April 2005

Microwave detectors generally measure power in the controlled impedance environments afforded by transmission lines and waveguides. The system impedance is known, so voltage and current magnitudes can be derived. With the judicious application of other microwave components such as power splitters and quadrature couplers, phase information can be extracted from multiple power measurements; therefore, full characterization of a system or component is possible with only the microwave detector to convert microwave signal characteristics to the readily observable and measurable quantities of low‐frequency voltages and currents.

Microwave detectors sense the amplitude or power of a signal, or the change in the amplitude or power of a signal. They are used for the determination of signal power level and for recovery of information placed upon the microwave signal amplitude.
Microwave Isolators
Authors: Dunn Vernon E.
Published: April 2005

Isolators are used extensively in microwave equipment to prevent interaction between other components of the system. This article describes the principles of operation of the most common types of microwave isolators and typical operating characteristics of these isolators.
Strip Transmission Lines
Authors: Pramanick Protap , Bhartia Prakash
Published: April 2005

Striplines are one of the most common types of transmission lines used in microwave circuits. This article presents the fundamental characteristics of this transmission line, together with equations for calculating these. Striplines are useful for designing virtually all microwave circuit components, which are described in the article.
Complex Media
Authors: Li Le-Wei , Yin Wen-Yan
Published: April 2005

This article reviews and summarizes the research and development work conducted in the area of microwave complex media, with emphasis on (1) clarification of bianisotropic media and (2) typical methodologies. Many application examples are included to address issues in the complex media, where partial solutions are provided as well.
Small Antennas
Authors: Fujimoto Kyohei
Published: April 2005

Small antennas are categorized into four types.

Electrically Small Antenna (ESA), Physically Small Antenna (PSA), Physically Constrained Small Antenna (PCSA), and Functionally Small Antenna (FSA). Although one uses four categories, the classification is not necessarily distinct, so that one class of antenna can be classified into more than one class; for instance, when a patch antenna has the edge (radiating aperture) of one‐fifth wavelength in its peripheral, the antenna is referred to as both ESA and PCSA.

Two major subjects exist in small antennas: (1) investigation of characteristics and performance of small antennas, and (2) exploitation of methods to attain small antenna, particularly ESA.
Integrated Antenna Systems
Authors: Fujimoto Kyohei
Published: April 2005

An antenna system is ordinarily designed independently from transmitter or receiver circuitry, to which the antenna is connected by a transmission line. Unlike such an ordinary antenna system, an integrated antenna system (IAS) incorporates components, either passive, active, or both, into the antenna structure. The term integration here implies unification of an antenna and device or circuitry so that the performance of the antenna system is determined by both the antenna and the integrated device or circuitry. By means of integration, one can expect either improvement or modification of the antenna characteristics, or enhancement of antenna performance due to the addition of functions introduced by the integration.
Antennas for Mobile Communications
Authors: Fujimoto Kyohei
Published: April 2005

Antennas used for mobile communications are not necessarily specialized types of antenna; ordinary antenna types can be used. However, there are several distinctions in performance between mobile and fixed communications with respect to design methodology for antennas in mobile communications, including variations of field strength, varied environmental conditions, mechanical and physical robustness, and mechanical and electrical system performance.
Dielectric Resonator Antennas
Authors: Ng H. K. , Leung K. W.
Published: April 2005

Linearly and circularly polarized conformal strip‐fed dielectric resonator antennas (DRAs) are studied in this article. In the latter case, a parasitic patch is used to excite a nearly degenerate mode. The hemispherical DRA, excited in its fundamental broadside TE111mode, is used for the demonstration. In the analysis, the mode‐matching method is used to obtain the Green's functions, whereas the method of moments is used to solve for the unknown strip currents. In order to solve the singularity problem of the Green's functions, a recurrence technique is used to evaluate the impedance integrals. This greatly increases the numerical efficiency. Measurements were carried out to verify the calculations, with good results.
Low Temperature Co‐Fired Ceramic (LTCC) Technology in RF and Microwave Engineering
Authors: Wu Ke-Li
Published: April 2005

This article outlines the low‐temperature cofired ceramic (LTCC) technology, from its historic evolvement to the basics of dielectric material properties and manufacturing process with emphasis on the design concept of multilayer LTCC RF and microwave embedded passive devices and modules. A detailed table containing most of commonly seen passive components is provided with layouts of their high‐frequency circuit models (Table 4 in the article).
Left‐Handed Materials for Microwave Devices and Circuits
Authors: Krowne Clifford M.
Published: April 2005

In this article we discuss the use of left‐handed materials or arrangements of materials to produce left‐handed responses to enable the construction of electronic devices and circuits. Attention is directed mainly toward the nonfocusing and nonradiating aspects of left‐handed behavior. Production of these materials, insertion of these materials in structures to produce devices and circuits, and the potential new properties of these electronic components and circuits is covered. The new physics causing the unusual aspects of left‐handed materials is presented. Propagation constants for microwave and millimeter electromagnetic waves will be presented, as well as electromagnetic field distributions in devices using left‐handed materials. Left‐handed devices and circuits, utilizing the physical action of left‐handed materials, will be discussed.
RF/Wireless Packaging
Authors: Pinel Stephane , Tentzeris Manos , Staicnlescu Daniela , Laskar Joy
Published: April 2005

The electronics packaging industry has proliferated to a point where its technology is at least equally—the semiconductor technology it is designed to serve. The increase in silicon complexity and integration has imposed demanding requirements on packaging technology for higher I/O counts, finer lead pitch, enhanced heat dissipation, and high‐speed, reliable interconnects. At the same time, the industry is also driving toward reduced printed‐circuit‐board area and complexity. From the traditional role of a protective mechanical enclosure, the modern package has been transformed into a sophisticated thermal and electrical management platform.

Recent advances in high‐frequency packaging indicate a migration from wirebond (where the chip or die is interconnected to the package only on the periphery of the die) to flip‐chip (where the die is interconnected to the package using the entire die area); and from ceramic to organic packages, with cartridge and multichip technologies emerging as key form factors.

The RF front‐end module is the core of the complex systems, and its integration poses a great challenge. Considering the characteristics of the RF modules, such as high performance up to 100 GHz; a large number of high‐performance discrete passive components, design flexibility, reconfigurable architecture, low power consumption, compactness, customized product, short time to market, and low cost, the system‐on package (SoP ) approach has emerged as the most effective means to provide a realistic integration solution as opposed to the system‐on‐chip (SoC ) solution. The strength of SoP is based on multilayer technololgy using low‐cost and high‐performance materials.
Smith Chart
Authors: Schwab Leonard M.
Published: April 2005

The Smith chart was routinely used to solve difficult transmission‐line matching problems in a variety of broadcasting, microwave, circuit design, and telecommunication applications. While it has since evolved almost exclusively into a software format, the original paper forms remain a convenient detailed medium for print output of finished work from software implementations of Smith's graphical method.

The essential objective in using the Smith chart is stated simply. An impedance (or equivalent admittance) locus over a frequency range is systematically repositioned on the chart in well‐defined ways by the progressive effects of series or shunt elements, thereby placing the passband portion of the impedance vector in the central area of the chart and the stopband portion at the outer periphery of the chart. The circuit elements commonly used include distributed elements such as transmission lines and quarter‐wave stubs, discrete elements such as inductors and capacitors, and any combination of these and related elements. Resistance elements are seldom intentionally used.
Measurement of Near Fields Using a Modulated Scatterer
Authors: Gardiol Fred
Published: April 2005

In the close vicinity of an electronic device or of an antenna, the electric and magnetic fields often exhibit a complex behavior, and a good knowledge of the resulting field pattern would be a most valuable asset for many practical applications. But when one inserts a probe antenna connected to a receiver, close to the the device, one modifies the filed, because metal locally short‐circuits the tangential electric field components.

The modulated scatterer technique provides an indirect approach to determine field components, by introducing a small “scatterer” that does not perturb as much as a receiving probe would. The signal returned by the scatterer is very small, and to detect it one “modulates” the scatterer and then uses coherent detection. The amplitude and the phase of the field components are then determined.
Application of Wavelets to Electromagnetic Problems
Authors: Goswami Jaideva C. , Tentzeris Manos M.
Published: April 2005

In this article, we discuss some wavelet applications to electromagnetic problems, provide an overview of wavelet theory, solve integral equations developing from electroagnetic scattering and transmission‐line problems, and consider differential equations.
Conformal Mapping Techniques
Authors: Yazgan Erdem , Akan Volkan
Published: April 2005

Conformal mapping techniques (CMTs) can be applied in the analysis of many engineering applications such as boundary value problems and electromagnetic field problems. This article presents information about the formulation of the potential and flux functions and the most important properties and application procedures of some RF and microwave engineering techniques.
Intermodulation
Authors: Pedro José Carlos
Published: April 2005

This article presents a broad overview of intermodulation distortion (IMD) in microwave and RF circuits and systems. It starts by putting IMD in the context of the linear and nonlinear perturbations of telecommunication systems, to then explain its physical origins and most common theoretical analysis methods and laboratory characterization setups. For that, several active device/system models and analytical and numerical techniques are addressed. Finally, the nonlinear distortion generation mechanisms present in typical microwave small‐signal amplifiers, high‐power amplifiers, and frequency converters are reviewed.
Ultra‐Wideband Radio
Authors: Siwiak Kazimierz
Published: April 2005

Ultrawideband (UWB) signaling is a modern wireless technique that reuses previously allocated RF bands by spreading the energy thinly in a wide spectrum, thus rendering signals imperceptible in the noise floor of conventional narrowband receivers. There are several methods of generating and radiating UWB signals, including a low‐duty‐cycle UWB implemented as time‐modulated UWB (TM‐UWB), and a high‐duty‐cycle direct‐sequence phase‐coded UWB (DS‐UWB). Even conventional radio techniques such as orthogonal frequency‐division multiplexing (OFDM) have been proposed, based on the “loose” spectrum access rules of the U.S. FCC Report and Order, which legalizes the emissions. Unique ways of coding and positioning the impulses, as in transmitted‐reference delay hopped UWB (TRD‐UWB), can result in the extremely simple UWB radio architectures. Here, the technological basics and performance of time‐position‐coded impulse UWB, the direct‐sequence‐coded UWB, and the transmitted‐reference UWB approaches are compared with conventional radio approaches. Several UWB approaches have been proposed in the IEEE 802 standards arena. Applications of UWB devices are presented and potential uses of UWB are described. Short‐pulse, low‐power techniques have enabled practical through‐the‐wall radars, centimeter precision 3D positioning, and communications capabilities at the high data rates, all with exceptional spatial capacities.
Miniaturized Packaged (Embedded) Antennas for Portable Wireless Devices
Authors: Ali M.
Published: April 2005

Packaged (embedded) antennas are becoming more and more in need with the rapid proliferation of wireless communication devices and systems. This include mobile phones, pagers, wireless PDAs, phones with enhanced GPS services, terminals with Bluetooth/WLAN functionalities, and RFID tags for inventory tracking and identification. In this article an overview of miniaturized packaged (embedded) antennas is presented. This includes multiband embedded antennas for mobile phone applications in the 900/1900‐MHz bands, Bluetooth/WLAN in 2.4‐ and 5–6‐GHz bands. Miniaturized planar inverted‐F antennas (PIFAs) are discussed along with wideband monopoles for possible triple‐band applications. Surface‐mount PIFAs, integrated inverted‐F antennas (IFAs), and packaged monopole type radiators are discussed for Bluetooth and WLAN applications. Finally, some future trends in this research area are also discussed.
Electromagnetic Bandgap Assisted Bandpass Filters
Authors: Karmakar Nemai C. , Nurunnabi Mollah Mohammad
Published: April 2005

Electromagnetic bandgap structures (EBGSs) are playing a vital role in enhancing the performance of microwave devices. EBG materials are periodic structures, that exhibit wide bandpass and bandrejection properties at microwave frequencies. The introduction of periodic perturbation such as dielectric rods, holes, and patterns in waveguides and PCB substrates has resulted in the development of EBGSs, which are also termed photonic bandgap (PBG) materials.