bluuebunny/crossref_metadata_2025 huggingface dataset:
Green's Function Methods
Authors: Jin Jian-Ming , Chew Weng Cho
Published: April 2005

The Greens function method is a powerful techniques for solving boundary value problems. Greens function was named after George Green (17931841), who developed a general method to obtain solutions of Poissons equation in potential theory. This method was described in an essay by Green entitled “On the application of mathematical analysis to the theories of electricity and magnetism,” published in 1828.
Ground Penetrating Radar
Authors: Daniels David J.
Published: April 2005

Ground penetrating radar (GPR) is a nondestructive measurement technique, which uses electromagnetic waves to locate targets or interfaces buried within a visually opaque substance or Earth material. GPR is also termedground probing,surface penetrating(SPR), or subsurface radar. A GPR transmits a regular sequence of low‐power packets of electromagnetic energy into the material or ground, and receives and detects the weak reflected signal from the buried target. The buried target can be a conductor, a dielectric, or combinations of both. There are now a number of commercially available equipments, and the technique is gradually developing in scope and capability. GPR has also been used successfully to provide forensic information in the course of criminal investigations, detect buried mines, survey roads, detect utilities, measure geophysical strata, and in other applications.
Gunn or Transferred‐Electron Devices and Circuits
Authors: Eisele Heribert
Published: April 2005

Transferred‐electron devices are the only microwave devices whose operation is based solely on the bulk‐material properties of semiconductors such as GaAs or InP. These devices are employed mainly in low‐noise medium‐power oscillators up to high‐millimeter‐wave frequencies. James B. Gunn was the first scientist to observe the underlying physical phenomenon in an experiment and, therefore, these devices are often referred to asGunn devices. This article describes the principles of operation, basic fabrication technologies, and common oscillator circuits for them. Different device structures for performance optimization and optimization procedures and simulation tools are discussed. The article also summarizes the current state of the art of Gunn devices and the outlook covers the prospects of more recent device structures and material systems.
Helmholtz Equations
Authors: Kowalczyk Piotr , Mrozowski Michal
Published: April 2005

Scalar and vector Helmholtz equations and their applications in electromagnetics are discussed. Relevance of the Helmholtz equation to wave motion is explained. Derivation involving Maxwell's equations and auxiliary scalar and vector potentials is presented. Basic analytical solution techniques for homogeneous and nonhomogeneous cases are introduced and illustrated in simple problems such as guided waves and radiation from a finite‐length dipole. Numerical methods and the operator approach to investigation of the Helmholtz equation are briefly outlined.
Heterojunction Bipolar Transistor
Authors: Prasad Jayasimha
Published: April 2005

The major advances in heterojunction bipolar transistor (HBT) technology since the mid‐1980s is covered in this article. The cutoff frequency (fT) and the maximum oscillation frequency (fmax) have reached record highs. Indium phosphide (InP) HBTs have shown (fT) and (fmax) in excess of 450 GHz and gate delays of 1.95 ps. Silicon–germanium (SiGe) HBTs have demonstrated 350 GHz (fT) and gate delays of 3.6 ps. The improved performance of the devices has resulted in impressive circuit results. Static frequency dividers operating at 152 GHz has been reported in InP HBT technology. SiGe HBT technology has demonstrated dynamic frequency dividers running at 110 GHz. Multiplexer/demultiplexer (MUX/DMUX) circuits operating at 40 Gbps (gigabits per second) were demonstrated with InP HBTs. On the other hand, 50‐Gbps 4–1 MUX/DMUX circuits have been shown with SiGe HBTs.
Heterostructures Devices
Authors: Ryzhii Victor
Published: April 2005

Heterostructures are the elements of many of the most advanced semiconductor devices currently being developed open and fabricated. They are essential parts of modern optoelectronic devices, such as semiconductor lasers, lightemitting diodes, and photodetectors with highest performance. Heterostructures are being employed increasingly in high‐speed digital and high‐frequency analog devices. The advantages of heterostructures are that they provide effective control over the states and motions of charge carriers—electrons and holes in active regions of heterostructure‐based devices.
High‐Field Effects
Authors: Hess K.
Published: April 2005

Electrons and holes contribute to the charge transport in semiconductors, while ordinary charge transport in metals is restricted to electrons only. Another distinctive feature of semiconductor transport is its inherent nonlinearity in high electric fields.

The basic phenomena of high field transport are nonlinear conductance; changed responses to magnetic fields; changed high‐frequency response, including the dielectric function; and changed confinement in potential wells or at heterojunctions between different semiconductors.
HTS Film Growth
Authors: Char Kookrin , Matijasevic Vladimir
Published: April 2005

In the decade since the discovery of high‐temperature superconductivity (HTS) in cuprate compounds, thin‐film materials have played an important role in the evolution of this field. The discovery of HTS has led to a rapid development of many different thin film deposition techniques. HTS thin films are now routinely made in hundreds of laboratories around the world, and thin‐film research is actively pursued in areas such as new superconducting materials and epitaxial oxide heterostructures. More recently, advances in deposition processes have brought about the synthesis of larger‐area HTS films, making fabrication less expensive and allowing for high‐throughput manufacturing of single‐superconducting‐layer films.

In this article, we review the physical vapor deposition (PVD) techniques most frequently used for HTS thin‐film synthesis.
History of Wireless Communication
Authors: Leggatt Patt
Published: April 2005

Beginning with the discoveries of Michael Faraday and then examining the work of the Maxwellians, Lodge, Fitzgerald, Heaviside, Hertz, Edison, Armstrong, and others, the history of wireless communications from 1831 to 1915 is presented. The article leaves off with Armstrong in 1915, whose triode oscillator paved the way for modern electronics and specifically wireless devices.
Indium Phosphide (InP)
Authors: Wada Osamu
Published: April 2005

Indium phosphide (InP) and InP‐based compound semiconductors grown on InP substrates are extremely important for the application to high‐speed, microwave, and optoelectronic devices. In the following, general properties of InP‐based materials and heterostructures are described first, and state‐of‐the‐art device and integrated circuit technologies for both electronic and optical systems are reviewed. High‐speed digital and microwave transistors such as high‐electron‐mobility transistors (HEMTs), heterojunction bipolar transistors (HBTs), and their integrated circuits have been developed for digital signal processing, including optical communications with the bit rate of 40–100 Gbps. Microwave devices for system applications in the frequency range up to 200 GHz are introduced. Long‐wavelength lasers and photodetectors, which are key in current optical communication networks, would have not become real without InP‐based compound materials covering the appropriate energy gap. Optoelectronic devices, including lasers, optical modulators, photodetectors, and their optoelectronic and photonic integrated circuits (OEICs and PICs) developed for bit rates up to 40 Gbps, are reviewed. Also, all‐optical devices being developed for the application to systems beyond 100 Gbps are described, which includes mode‐locked lasers and ultrafast all‐optical optical switches based on unique ultrafast properties of InP‐based materials.
Integro‐Differential Equations
Authors: Garcia Manuel
Published: April 2005

This article discusses a variety of methods and approximations used to solve and calculate integrodifferential equations, with emphasis, is on the utilitarian rather than the theoritical. Integrodifferential equations can describe linear and nonlinear systems that have memory, or are not in equilibrium. The appearance of both derivatives and integrals in an equation (e.g., expressing some type of balance with respect to time) means that instantaneous rates (e.g., velocity) and accumulated history (e.g., metal fatigue) determine the state of the system at the present moment. It is this aspect of integrodifferential equations that gives them their intellectual appeal, wide applicability, and challenging nature.
Intermodulation Measurement
Authors: Taher Abuelma’atti Muhammad
Published: April 2005

Whenever a number of signals of differing frequencies pass through a nonlinear device, energy is transferred to frequencies that are sums and differences of the original frequencies, that is, intermodulation products. Using a Taylor series expansion, this article presents a simple intermodulation theory and discusses its limitations and extensions. Methods of characterizing and measuring the intermodulation performance of nonlinear devices are presented, and their merits and demerits are discussed.
Iterative Methods
Authors: Burkholder Robert J. , Lee Jin‐Fa
Published: April 2005

Iterative solution algorithms are described for complex systems with a large number of degrees of freedom. Areas of application include partial differential equations, integral equations, and hybrid methods in electromagnetics. Classical (or stationary) methods and conjugate gradient (nonstationary) methods are presented. Classical methods are generalized in terms of matrix splittings. The conjugate gradient method is derived in detail from the point of view of Galerkin testing and Krylov spaces. Preconditioning is discussed, and some common preconditioners from classical methods are presented.
Leaky Wave Antennas
Authors: Galli Alessandro , Frezza Fabrizio , Lampariello Paolo
Published: April 2005

The basic radiative features, operation, design, and realization procedures of leaky‐wave antennas for microwave applications are described. The relations between the propagation properties of open waveguides, on which these antennas are based, and the relevant radiation patterns are discussed, exploiting the leaky‐wave concept. The main radiative characteristics (scanning behavior, beamshaping, etc.) are presented, and the procedures for analysis and synthesis are outlined. Examples of proposed structures are reported, and accounts for practical operation and measurements are given.
Lens Antennas
Authors: Malherbe J. A. G.
Published: April 2005

Lenses can be employed to act as high‐gain scannable antennas. The optical principles that apply to lens antennas are discussed, as well as the materials used in the construction of lenses. The basic lens function is discussed, and examples given of simple planoconvex and planoconcave lenses, together with the equations that describe the lens surfaces. In order to reduce the lens size, lenses are zoned, and equations for lens zoning are given. Other lens parameters such as gain, sidelobe level, reflections, loss, and bandwidth are treated. Lens systems for scannable or multibeam antennas are described, and design and analysis procedures for Rotman lenses given. Other lenses discussed include Luneburg,R‐2R, integrated dielectric, and Fresnel zone lenses.
Low Noise Amplifiers: Device Noise Characterization and Design
Authors: Lee Sungjae , Webb Kevin J.
Published: April 2005

The basic procedures for device noise characterization and the design of low noise amplifiers are described.
Low‐Pass Filters
Authors: Choi Chiu H.
Published: April 2005

A lowpass filter suppresses the high‐frequency components of a signal, leaving intact the low‐frequency ones.

An approach to design a circuit (a lowpass filter) whose frequency response satisfies the lowpass requirements consists of two steps: approximation of the requirements by a transfer function and synthesis of the transfer function.

There are several approximation methods, for instance, Butterworth, Chebyshev, inverse Chebyshev, and Cauer approximations. A transfer function obtained by one method is different from those obtained by the others, and has different properties. However, the frequency response of each of the transfer functions satisfies the lowpass requirements.
Magnetic Field Measurement
Authors: Stecher Manfred
Published: April 2005

The measurement of electromagnetic (EM) fields is relevant for various purposes: for scientific and technical applications, for radio propagation, for electromagnetic compatibility (EMC) tests (i.e., testing of the immunity of electronic equipment to electromagnetic emissions aiming at the protection of radio reception from radio interference), and for safety reasons (i.e., the protection of persons from excessive field strengths). For radio propagation and EMC measurements, below about 30MHz a distinction is made between electric and magnetic components of the EM field to be measured. In the area of human safety, this distinction is continued to even higher frequencies.
Magnetic Materials
Authors: van Dover Robert B.
Published: April 2005

Since the early part of the twentieth century, magnetic materials have been the subject of deep and broad research and development because of their economic and scientific importance, and much of our knowledge is mature. Nevertheless, startling discoveries continue to be made, such as the discovery of Nd–Fe–B permanent magnets and the “giant magneto‐resistance” effect in thin‐film multilayers.
Magnetic Microwave Devices
Authors: How Hoton
Published: April 2005

Magnetic microwave devices discussed in this article include ferrite junction devices, lumped‐element circulators, nonreciprocal resonators, YIG film and MSW devices, magnetooptic devices, absorbing/antireflection layers, and nonlinear magnetic devices. A general theoretical background underlying the physics for the operation of a ferrite microwave device is first reviewed. Discussions include the derivation of the Polder permeability tensor, the effective fields associated with electron spin motion, the general dispersion spectrum and plane‐wave solutions for electromagnetic wave propagation in a bulk magnetic medium, MSW (magnetostatic waves) admitted by the geometry of a yttrium iron garnet (YIG) film, and the nonlinear instabilities for spin waves occurring at high power, including their routes to chaos. Ferrite junction devices including circulators and isolators are discussed in terms of their bandwidth operation, size reduction, power handling, and other novel issues such as intermodulation noise. The operation of lumped‐element circulators is introduced and the interport impedances outlined. The effective field associated with a magnetic easy plane is defined from an operation point of view. A ferrite nonreciprocal resonator can be used as a phase shifter whose operation is independent of the derived phase shift angles. YIG film devices incorporating magnetostatic waves are introduced, including delay lines, filters, directional couplers, and resonators. Nonlinear magnetic devices are discussed, including frequency‐selective power limiters, signal‐to‐noise enhancers, amplitude correctors, and ferrimagnetic echoing devices. Magnetic solitons include Bloch domain wall solitions and microwave magnetic envelope solitons. Finally, magnetooptic Kerr and Faraday effects and the operation of magnetooptic Bragg diffraction devices are discussed, and the design of microwave absorbing layers and antireflection layers is briefly introduced.
Magnetic Resonance Imaging
Authors: Webb Andrew
Published: April 2005

This article describes the basic theory behind magnetic resonance imaging and highlights the most recent advances in hardware design and image acquisition strategies for increased speed and signal‐to‐noise ratio.
Microstrip Antenna Arrays
Authors: Hall Peter S.
Published: April 2005

Microstrip antenna arrays offer low‐profile solutions to many antenna applications with potentially low cost. Their low profile comes about from the use of microstrip patch radiators fed by microstrip circuit‐based feed networks, or by using the naturally occurring radiation from the feed networks to form a beam. Both patches and microstrip feeds consist of metallic strips or shapes photoetched on one side of a grounded substrate and can be made using conventional photolithographic processes. The use of the microstrip transmission‐line medium, widely used in both hybrid and monolithic radiofrequency circuits, also gives rise to a unique potential for integration with active devices and radio front ends.

This article gives an overview of microstrip array architectures. These include parallel‐ and series‐fed arrays and also arrays formed by discontinuities in a microstrip line, such as the serpent and rampart lines. Other forms such as ultrawideband arrays, leaky‐wave arrays, multilayer arrays, sequentially rotated arrays, multibeam arrays, reflect arrays, and active integrated arrays are also described. The article concludes by describing the impact on array design of important factors such as accuracy in pattern synthesis, feed loss and radiation, and mutual coupling.
Microwave Filters
Authors: Zhu Lei
Published: April 2005

This article summarizes the fundamentals of microwave filters with varied frequency‐selective characteristics such as lowpass, bandpass, highpass, and bandstop. On the basis of the ladder network of a lowpass prototype filter, a well‐known synthesis design approach is described to realize the lowpass frequency response in terms of the preselected insertion loss functions and then determine the element values of this network under the Butterworth and Chebyshev function responses. By executing the frequency transformation from the normalized to actual microwave frequency ranges, various lumped‐element microwave filters are first constructed with both series and shunt elements. Next, the immittance inverters are introduced and utilized to eliminate either series or shunt elements, thus alleviating the complexity in filter implementation. In addition to a series of useful design formulas and tables provided with brief explanations, a variety of practical microwave filters are made up using transmission‐line and waveguide elements and their principles are discussed with regard to their equivalent cascaded networks.
Microwave Power Transmission
Authors: Strassner Berndie H. , Chang Kai
Published: April 2005

Microwave power transmission (MPT ) is the wireless transfer of large amounts of power at microwave frequencies from one location to another. MPT is often referred to in the literature as wireless power transmission (WPT ) at microwave frequencies. MPT research has been driven primarily by the desire to remotely power unmanned aerial vehicles (UAV s) and by the concept of space solar power (SSP ) first conceived by Dr. Peter Glaser of the Arthur D. Little Company in 1968. SSP is an MPT system with the addition of solar cells and magnetrons for microwave power generation. The SSP idea calls for a constellation of solar power satellites (SPS s) to capture the energy from the sun using arrays of solar cells. The solar cell panels output large DC voltages to awaiting cavity magnetrons positioned on various subarrays within each SPS phased‐array aperture. These magnetrons convert the high‐voltage DC outputs of the solar panel arrays to microwave power. The microwave energy is then beamed to Earth to farms of rectifying antenna (rectenna) arrays that convert the incoming microwave energy back to DC power. Since its inception, SSP has gained considerable attention since it has the potential of providing clean, renewable, and continuous power for generations to come. MPT has been shown experimentally as a way for people on Earth to remotely power unmanned high‐altitude platforms such as UAV s. Additional uses for MPT include powering space probes from future space stations into deep space and powering robots to enter dangerous environments such as nuclear‐contaminated areas.
Mixed‐Signal CMOS RF Integrated Circuits
Authors: Steyaert Michiel , Reynaert Patrick
Published: April 2005

The world of wireless communication and its applications have begun to grow rapidly. The driving force behind this lies in the introduction of digital coding and digital signal processing in wireless communications. This digital revolution is driven by the development of high‐performance, low‐costCMOStechnologies that allow for the integration of an enormous amount of digital functions on a single die. AsCMOSis mainly a digital technology, placing all digital functions on a single die is merely a matter of handing the system complexity. To achieve a truly single‐chip solution, the analog part also has to be integrated inCMOS.

The telecommunication market is generally considered to be a business where a single‐chip solution in a cheap (CMOS) technology results in a huge cost benefit; the main reason is the high volume of user equipment. Furthermore, in these systems, small size, low board area, low power consumption, and high talktime are crucial, and therefore it is of utmost importance to achieve a high level of integration. This trend toward single‐chip, fully integrated systems can clearly be seen in the development of RF systems such asGSM,EDGE, Bluetooth, and wirelessLAN. In all these sytems, the analog part mainly consists of anRFfront end. Deep submicrometer technologies allow for the operation frequency ofCMOScircuits above 1 GHz, which opens the way to fully integratedRFsystems. Several research groups have developed high‐performance downconverters, low‐phase‐noise voltage‐controlled oscillators, and dual‐modulus prescalers in standardCMOStechnologies. The research has already demonstrated fully integrated receivers and synthesizers with no external components, nor tuning or trimming. Further research on low‐noise amplifiers, power amplifiers, and synthesizers has resulted in fully integratedCMOSRFtransceivers for DCS1800, Bluetooth, and wirelessLAN.

In this article, we focus on the evolution from the well‐known heterodyne receiver topology to the zero‐ and low‐IF topology used in modern receivers. We also discuss the interaction between the analog part and the digital part regarding substrate noise and decoupling.
Mobile Satellite Communications
Authors: Lodge John
Published: April 2005

Mobile satellite (MSAT) AU:1 systems provide communications services to mobile and portable terminals using a radiotransmission path between the terminal and the satellite.

A wide variety of services and applications are supported by mobile satellite systems, with many more proposed.

Third‐generation systems are expected to be capable of transmission at rates up to several hundred kilobits per second and will be capable of delivering moderate‐quality video and high‐quality audio services.

A wide variety of mobile satellite terminals is commercially available.
Monopole Antennas
Authors: Gandhi O. P. , Lazzi G. , Furse C. M.
Published: April 2005

This article describes the concepts underlying monopole antennas and their many applications, such as for broadcasting, car radios, and more recently for cellular telephones.
Monte Carlo Analysis
Authors: Lugli Paolo
Published: April 2005

As the name suggests, the Monte Carlo (MC) method is based on the selection of random numbers [1–4]. In its present form, the method is attributed to Fermi, Von Neumann, and Ulam, who developed it for the solution of problems related to neutron transport.

Although it will not be possible to exhaust the complexity of the MC methods in such a short review, the present contribution is intended to give a critical overview of the MC algorithms used for device and process modeling and for circuit yield analysis.
Multiconductor Transmission Lines
Authors: Brandão Faria J. A.
Published: April 2005

This article is devoted to the analysis of multiconductor transmission lines (MTLs), a type of structure that is encountered in many applications concerning RF and microwave engineering. Our aim is to provide the reader with a self‐contained presentation of the subject; we start by establishing the time‐domain equations of multiconductor transmission‐line systems and then progress step by step to the final objective of determining the frequency‐domain solution to those equations. Matrix techniques are made intense‐use in order to permit a compact analysis of the problem. Solutions to MTL equations are presented in two different useful formats. At first we consider a solution in the form of a superposition of natural modes of propagation; later, a relationship between voltages and currents at the MTL structure ports is established by employing a transmission matrix. The analysis presented in this article is not limited to the simple case of uniform line structures, as it also encompasses the important problem of nonuniform MTLs.
Dual‐ and Multi‐Frequency Microstrip Antennas
Authors: Lee K.F. , Luk K.M. , Shum Y.H.
Published: April 2005

A number of techniques for dual‐band or multiband operation of microstrip antennas are available in the literature. This article introduces the operation principles and design guidelines of several popular methods, including the multimode‐operated patch, stub‐loaded patch, slot‐loaded patch, stacked patch, and coplanar patch antenna. Their relative performances are compared both theoretically and experimentally. One important purpose of the article is to provide physical insight to readers for further development of multiband microstrip antennas, which are attractive for modern wireless applications.
Multiplexers
Authors: Mansour Raafat R.
Published: April 2005

Multiplexers are used in communication system applications where there is a need to divide a wideband signal into a number of narrowband signals (channels). They are also employed to provide the opposite function, by combining several narrowband channels into a single wideband channel. Multiplexers are therefore known aschannelizersorcombiners. They find widespread use in many applications such as satellite payloads, wireless systems, and electronic warfare (EW) systems.
Negative Resistance
Authors: King Clifford A. , Ng Kwok K.
Published: April 2005

It is understood that the term negative resistance refers to the dynamic characteristic, that is, the slope of the
I–V
curve (
dV/dI
) is negative.

The negative resistance devices originating from
dV/dI
being negative are discussed, followed by their applications. Finally, similar discussions on the transit‐time devices are presented.
Noise, High‐Frequency
Authors: Agethen M. , Reuter R. , Bertenburg R. M. , Brockerhoff W. , Tegude F. J.
Published: April 2005

The high‐frequency behavior of electronic devices is of major interest in the field of research and development. Beside the typical RF device parameters, like the cutoff frequenciesfTandfmax, the high‐frequency noise behavior should be considered for circuit design, especially if noise has a significant influence on the system performance, for instance, the sensitivity of receivers. Thus, there is a demand for simple, but exact RF noise models that must consider the physically relevant noise phenomena with a significant contribution to the total noise behavior of the device.

After an introduction to various physical noise sources, a general description of noisy two‐ports will be presented. Then, a short presentation of a special measurement setup for RF noise in the range of 2–18 GHz with dependence on temperature (15–400 K) is given. In Section 4 RF noise phenomena in certain devices are examined and high‐frequency noise models for heterostructure field‐effect transistors (HFETs) and heterojunction bipolar transistors (HBTs) based on the material system InP are presented. For both devices the capabilities of the model presented will be proved by comparing measured and modeled RF noise parameters. In Section 5 modifications of the HFET noise model and applications of this RF noise model are presented.
Microwave Parametric Amplifiers
Authors: Faber Marek T.
Published: April 2005

An outline of the development of microwave parametric amplifiers (paramps) is presented as an introduction. The principle of their operation is explained leading to the classification of parametric amplifiers and frequency converters. (Photoparametric amplification is also referenced.) Varactor diodes are briefly presented in order to discuss in greater detail the operation of the most significant type of paramp—the nondegenerate parametric amplifier—including gain, noise, bandwidth, and stability. Degenerate, multiple‐idler and traveling‐wave parametric amplifiers are also discussed. Then the construction of a 3.25‐GHz nondegenerate parametric amplifier is presented as a representative example.
Passivation
Authors: Pearton S. J.
Published: April 2005

Passivation layers are deposited over the entire top surface of Si or compound semiconductor wafers to form an insulating protective coating for the semiconductor. This procedure guards against environmental contamination that might lead to increased surface leakage currents, and also against mechanical damage during assembly and packaging. Some of the desirable properties of passivation‐layer materials include good scratch protection of the underlying interconnect metallurgy, impermeability to moisture and alkali (Na+, K+) ions, low stress (<5×108 dyn/cm2, preferably compressive), conformal step coverage, and etchability with excellent uniformity and adhesion. While thicker passivation layers would normally be desirable because of the improved mechanical protection they afford, there is generally an upper limit to the thickness in order to avoid cracking. The primary inorganic dielectric passivation films are SiO2and SiNx, while polyimides and epoxy resins are used for low‐cost polymer encapsulation. The thermal stability requirements are obviously lower for final passivation coatings than for interlevel dielectrics.

Patterns are formed in the passivation‐layer material by either wet (for phosphosilicate glasses) or dry (for SiNxor polymers) etching to enable electrical contact to the completed circuit. The area of these contact pads is sufficiently large (100×100 μm2) that wet etching is acceptable.
Perturbation Theory
Authors: Mathew K. T.
Published: April 2005

Perturbation methods, otherwise known as cavity perturbation methods based on perturbation theory, are simple and accurate methods to solve many of the electromagnetic field problems. This article envisages the basic concepts to evolve the perturbation theory from Maxwell's fundamental equations. Different approaches to this problem are also tackled. The merits, drawbacks, and possible errors of this technique and few of important applications are discussed.
Phase‐Locked Oscillators and Frequency Synthesizers
Authors: Rohde Ulrich L.
Published: April 2005

Synthesizers are used to generate frequencies with arbitrary resolution covering the frequency range from audio to millimeter‐wave. Today, simple frequency synthesizers consist of a variety of synthesizer chips, an external voltage‐controlled oscillator (VCO), and a frequency standard. There are also combinations of techniques that I would like to refer to as “hybrid synthesizers.” They will be covered here.
PIN Diodes
Authors: Fathy Aly E. , Rosen Arye
Published: April 2005

A PIN diode is a semiconductor device that operates at RF and microwave frequencies as a variable resistor in the forward direction.

The PIN diode is useful for leveling, limiting, and amplitude modulating an RF signal, when the control current is varied continuously. However, the device can be used for pulse modulating, attenuating, and phase shifting of an RF signal if the control current is turned ON or OFF, or in discrete steps. In addition, the PINs small size, weight, high switching speed, and minimized parasitic elements make it ideally suited for miniature, broadband RF signal applications.
Q‐Factor Measurements
Authors: Luiten Andre
Published: April 2005

This article presents a review of both traditional and modern methods ofQfactor measurement. Many of the techniques to be described were first developed in order to determine theQfactors of resonances falling in the microwave frequency domain.

The article commences with a definition of theQfactor and a description of the experimental parameters that need to be measured so as to determine theQfactor of resonance. The various methods for measuring these parameters will then be outlined, including the particular advantages and disadvantages of a technique, the equipment required for the measurement, and its potential for accuracy. Finally, some of the latest developments in the field ofQmeasurement will be presented.
Radar Altimetry
Authors: Raney R. Keith
Published: April 2005

The article reviews ocean‐observing radar altimeters hosted on spacecraft in low‐Earth orbit. These instruments measure sea surface topography on global and mesoscales to a height accuracy of a few centimeters. Flight missions since 1973 to the present are summarized. The conventional pulse‐limited full‐deramp modulation technique is illustrated by the design of the TOPEX altimeter. The advanced delay–Doppler technique is explained, whose benefits extend to ice‐sheet altimetry (Cryosat), and to improved measurement of oceanic gravity anomalies, hence bathymetry. The article concludes with comments on future directions.
Radar Cross‐Section
Authors: Jenn David C.
Published: April 2005

Radar cross section (RCS) is a measure of the magnitude of the scattered electromagnetic wave from a body relative to the magnitude of the wave incident on the body. To many people RCS is synonymous with stealth. Stealth technology has become an integral part of all military systems since it was first employed in the 1970s. However, RCS is just one aspect of stealth, the design philosophy that seeks to make a platform (such as an aircraft, ship, or ground vehicle) undetectable to a wide range of sensors.
Radar Remote Sensing of Irregular Stratified Layers
Authors: Bahar Ezekiel
Published: April 2005

A variational full‐wave approach to electromagnetic scattering from irregular stratified media with multiple scale features is presented. Since the scales of the irregular features, such as surface roughness, are often a continuum from very large to very small compared to the wavelength, a two‐scale unified full‐wave approach is applied. The method used to smoothly decompose the random medium fluctuations into larger‐scale and smaller‐scale fluctuations is illustrated for random media characterized by Gaussian and Pearson–Moskowitz‐type spectral density functions. The variational parameter is related to the two‐scale subdivision of the random features of media. It is shown that the total scatter cross section of the irregular stratified media is stationary over a very broad range of the variational parameter. Thus the full‐wave solutions, which are expressed as weighted sums of two cross sections, are practically insensitive to the precise decomposition into two‐scale features.
Radar Signal Detection
Authors: Wang Minsheng , Chan Andrew K.
Published: April 2005

Owing to the existence of noise and interference, radar signal detection has to be treated as a statistical problem, regardless of whether the signal under detection is deterministic. This statistical formalism of radar signal detection theory can be applied to all types of radar signals without restriction. To understand radar signal detection, noise has to be described quantitatively. A time‐limited deterministic signal can be described as a time series, and a periodic deterministic signal can be represented as a Fourier series. In contrast, noise cannot be represented as a deterministic function in the time or frequency domains. In other words, we cannot predict a noise‐contaminated radar signal with absolute certainty. However, with available noise information such as the expectation, the power, or even the probability distribution of noise, we can select a criterion on which to base our decision.
Radar Tracking
Authors: Bruder Joseph A.
Published: April 2005

Radar tracking is the ability to determine the position and velocity vector of a target at any particular instant in time, to predict its position in the future, and to distinguish the desired target from other targets and clutter.

Target tracking is necessary for a number of reasons. In order to direct a weapon such as a missile or a projectile to a target, the range, future range, and angles from the radar to the target must be determined by the radar. By knowing the position of the target relative to that of the missile, the guidance computer can direct the missile to the target.
Radiation Effects
Authors: Schwank James R. , Sexton Fred W. , Dodd Paul E. , Shaneyfelt Marty R.
Published: April 2005

The effects of the space radiation environment on semiconductor device response are reviewed. Semiconductor devices in space can be exposed to energetic particles that can cause device degradation and system failure. The space environment consists primarily of protons, electrons, and heavy ions. Ionizing radiation (electrons and protons) can induce significant charge buildup in oxides, causing large threshold voltage shifts, and decreases in carrier mobility and bipolar transistor gain. This can result in large increases in the static power current of an IC, degradation in timing, and potential loss of functionality. In the space environment, heavy ions and protons can cause single‐event effects. There are two general classes of single‐event effects: soft errors and hard errors. Soft errors cause no permanent damage and may be correctable. Single‐event upsets are one type of soft error. If the error rate caused by soft errors is too high, performance degradation and even system failure can result. Hard errors cause permanent damage to devices. As integrated circuit technologies advance, they are becoming more prone to soft errors caused by energetic ions. In fact, soft errors caused by energetic particles present in the terrestrial environment and emitted from metal impurities are rapidly making single‐event upset a major reliability concern for ground‐based commercial ICs.
Radio Reception
Authors: Zvonar Zoran
Published: April 2005

Several factors could influence the radio system performance, including radio propagation, radiolink design, radio receiver design, as well as radio network design. The focus of this section is on the most important elements of the radio‐access portion of the system.

Section 1 covers link budget and frequency planning. Sections 2–4 address path‐loss prediction models, outdoor and indoor prediction models, effects of environment and small‐scale variations resulting in multipath fading, with emphasis on channel characterization and statistical propagation models. Section 5 completes the list of external factors that influence radio performance. The aspects of radio design include radio parameters, diversity techniques, modulation and coding, and interference suppression techniques.
Radiowave Propagation Concepts
Authors: Levis Curt A.
Published: April 2005

Although radiowaves also propagate in waveguides, cables, and transmission lines, the term radiowave propagation is used generally, and specifically in this article, for signal travel between a source and a receiver without guidance by such artificial devices. Examples of such systems are radio and television broadcasting, radio point‐to‐point communication, radar, radio navigation, and remote sensing. Much has been learned about radiowave propagation since Hertz first demonstrated wireless transmission from one room to another. Now radiowave propagation is considered a moderately mature science, yet new understanding continues to emerge. This article presents an overview of radiowave propagation concepts.
Radiowave Propagation Ground Effects
Authors: Hill David A.
Published: April 2005

Radiowave propagation plays an important role in modern communication, radar, and navigation systems. The mathematical theory of radiowave propagation is based on Maxwells equations [1], which were formulated by James Clerk Maxwell in the 1860s [2]. The first free‐space radiowave transmission experiments between a pair of antennas were performed by Heinrich Hertz in the 1880s [3]. In 1897 Marconi first patented a wireless telegraphy system based on long‐distance, radiowave propagation.
Radiometry
Authors: Glover Ian A.
Published: April 2005

Radiometry is concerned with the measurement, analysis, and interpretation of radiant electromagnetic energy. The simplest and most common measurement, made using an instrument called aradiometer, is of received electromagnetic power in a given frequency band. Some instruments, however, analyze the received energys spectral distribution (spectroradiometers), its polarization (polarimeters), or its angular distribution in space (imaging radiometers). The usual objective of radiometric measurements is the inference from them of the physical and/or chemical state of the material from, or through which, the received electromagnetic energy has been emitted, reflected, or transmitted. Radiometry is therefore a branch of remote sensing and could be considered to include radar.
Rectifying Antennas (Rectennas)
Authors: Strassner Bernd H. , Chang Kai
Published: April 2005

Rectifying antennas, commonly referred to asrectennas, are integral parts of microwave power transmission or wireless power transmission (WPT ) systems. In WPT systems, RF power is transmitted from one location and captured at another location. The term rectenna consists of parts of the words “rectifier” and “antenna” since its function is to absorb incoming radiofrequency (RF ) energy and convert this energy to usable DC power. Advanced concepts for WPT , in which rectennas play a vital role, include the ground–space applications of powering aircraft and high‐altitude platforms remotely as well as space solar power where the sun's energy is transmitted from space in the form of microwaves to Earth's surface. WPT can also be useful in several ground–ground applications, including supplying power to remote locations such as islands where the infrastructure to generate power is either absent or not cost‐effective to build. However, the main future use for WPT is seen in a myriad of space–space applications. These include supplying power to space colonies and space shuttles from nuclear powered satellites. This will enable space explorers to obtain the necessary power needed, at locations far from Earth, to further explore the depths of space.
Reflector Antennas (Parobolic Antennas, Dish Antennas)
Authors: Terada Marco A. B.
Published: April 2005

A primer on the reflector antenna art is presented in this article. The initial sections offer an overview of reflector antennas and their main applications at a level suitable for high school and lower‐division college students, as well as the basic principles necessary for the proper understanding of their functionality. The following sections present a more in‐depth treatment of the subject, including methodologies for analyzing and designing practical reflector systems. Finally, advanced topics covering the current state of the art within the field are discussed at a level targeting both graduate students and researchers, as well as the practicioning engineer. An effort is made to illustrate the theory and discussions with examples reflecting real‐world applications.
Resonant Tunneling Diodes
Authors: Maezawa Koichi
Published: April 2005

Resonant tunneling diodes (RTD s) exploit the quantum tunneling effect emerging in nanometer‐scale thin semiconductor heterostructures. The RTD s feature strong nonlinear current–voltage characteristics exhibiting negative differential resistance and also extremely high operation frequency. These features make the RTD s extremely useful for nonlinear microwave/millimeter‐wave circuits as well as high‐speed digital circuits. The features of RTD s and their applications to high‐frequency circuits are discussed.
Resonators
Authors: Ahn Hee-Ran
Published: April 2005

Resonators are important components in microwave communication circuits. They create filters and select frequencies in oscillators, amplifiers, tuners, and so on. Fields inside a resonator store energy at the resonance frequency where equal storage of electric and magnetic energies occurs. The input impedance at resonance is purely real because the reactance is proportional to the difference between electric and magnetic energy storage.

In this article, series and parallel resonance circuits will be discussed and then the representative resonators that are commonly used in practical cases will be explained.
Silicon‐Germanium
Authors: Schumacher Hermann
Published: April 2005

The introduction of Silicon‐Germanium alloys into the base of bipolar transistors provided a quantum leap in the performance of microwave and millimeter‐wave integrated circuits based on mature Silicon processing. Silicon/Silicon‐Germanium heterostructures can be used in a variety of ways. In bipolar transistors, they may increase the allowable base doping concentration, or speed up charge carrier transport through the base layer. In field‐effect transistors, they may provide carrier confinement, reducing Coulomb scattering and thus increasing the low‐field mobility of electrons and holes. Or, they may be used to introduce an axial strain into Silicon channel layers, again with advantages in charge carrier mobility. The article reviews the principle of SiGe‐based electronic devices, their state‐of‐the‐art, and some microwave circuit applications.
Six‐Port Networks
Authors: Xu Xinyu , Wu Ke , Bosisio Renato G.
Published: April 2005

Software‐defined radio (SDR) has been identified as a potential method to enhance flexible wireless communication systems. The operation speed of an analog/digital converter (ADC) and processing ability of digital signal processing (DSP) chips are key factors in the development of SDR for useful commercial applications. More recent advances in semiconductor processing technology and the development of reconfigurable devices such as digital signal processors and field‐programmable gate arrays (FPGAs) reduce the development time of commercial products. SDR in conjunction with six‐port receivers has promising applications for use in wireless LANs, audio and television broadcasting, and interoperability between different radio services, as seen by new studies on the use of six‐port technology in various design aspects of a new SDR receiver. The objective is to realize an application of SDR to provide a multichannel, multimode wireless direct digital receiver.

The combination of SDR and six‐port technology provides great flexibility in system configuration; significant reduction in hardware cost, particularly at millimeter‐wave frequencies; and potential for software reuse. The six‐port receiver approach offers wideband accommodation to ever‐changing communication specifications required in a SDR as much of its functionality is defined in software. Different types of six‐port circuits have been designed, with center frequencies at 2.4, 5.8, 24, and 28 GHz, operating over wide frequency bands. Some six‐port circuits are based on microstrip structures and are fabricated with hybrid microwave integrated circuit (MHMIC) or monolithic microwave integrated circuit (MMIC) technology at both microwave and millimeter‐wave frequencies. Other circuits use a novel substrate‐integrated waveguide (SIW) structure allowing integration of planar integrated circuit structure with waveguide structure. The performances of these six‐port circuits in digital receivers are reported in relation to signal modulation schemes, noise performance analysis calibration, and coding. Bit error rate simulation and measurement results obtained with demodulation algorithms are given for QPSK and QAM‐16 signals under a variety of operating conditions. Initial results show promising applications of six‐port technology for direct digital conversion demodulation reception, needed in future low‐cost SDR communication systems. Measurement and simulated demodulation results obtained with coding algorithms are also given.