Showing papers in "IEEE Antennas and Propagation Magazine in 1994"
TL;DR: In this paper, two approaches for describing the time-domain performance of an antenna were described, one of which uses the transfer function, a function which describes the amplitude and phase of the response over the entire frequency spectrum, and the other one uses time domain parameters, such as efficiency, energy pattern, receiving area, etc.
Abstract: Frequency-domain concepts and terminology are commonly used to describe antennas. These are very satisfactory for a CW or narrowband application. However, their validity is questionable for an instantaneous wideband excitation. Time-domain and/or wideband analyses can provide more insight and more effective terminology. Two approaches for this time-domain analysis have been described. The more complete one uses the transfer function, a function which describes the amplitude and phase of the response over the entire frequency spectrum. While this is useful for evaluating the overall response of a system, it may not be practical when trying to characterize an antenna's performance, and trying to compare it with that of other antennas. A more convenient and descriptive approach uses time-domain parameters, such as efficiency, energy pattern, receiving area, etc., with the constraint that the reference or excitation signal is known. The utility of both approaches, for describing the time-domain performance, was demonstrated for antennas which are both small and large, in comparison to the length of the reference signal. The approaches have also been used for other antennas, such as arrays, where they also could be applied to measure the effects of mutual impedance, for a wide-bandwidth signal. The time-domain ground-plane antenna range, on which these measurements were made, is suitable for symmetric antennas. However, the approach can be readily adapted to asymmetric antennas, without a ground plane, by using suitable reference antennas. >
329 citations
TL;DR: In this article, a critical review of available solutions and design techniques for the Jauman problem is presented, and three new and efficient algorithms, dedicated to the problem, which synthesize absorbers with Butterworth, equiripple or Chebyshev absorption characteristics are presented.
Abstract: The paper presents a critical review of available solutions and design techniques. It then outlines three new and efficient algorithms, dedicated to the Jauman problem, which synthesize absorbers with Butterworth, equiripple or Chebyshev absorption characteristics'. Upper limits exist on the spacer dielectric constant for these solutions to be realizable, and are tabulated. An example of the results obtained, in the form of a design table for practical Chebyshev absorbers, is also presented. These designs are optimal in the sense of maximum bandwidth for fixed passband reflection coefficient magnitude. >
208 citations
TL;DR: In this article, the authors summarized radio-propagation measurements and models for emerging wireless personal communication systems, and the problem of RF penetration into buildings is identified as an important area of research.
Abstract: The present survey paper summarizes radio-propagation measurements and models for emerging wireless personal-communication systems. Both indoor and microcell-propagation environments are considered, and the problem of RF penetration into buildings is identified as an important area of research for emerging wireless-communication systems. >
120 citations
TL;DR: In this article, the integral equation for a hemispherical dielectric-resonator antenna (DRA), excited by either a coaxial probe or a slot aperture, is obtained.
Abstract: An overview is given for the development of dielectric-resonator antennas. A detailed analysis and study of the hemispherical structure, excited by a coaxial probe or a slot aperture, is then given, using the dyadic Green's functions pertaining to an electric-current source or a magnetic-current source, located in a dielectric sphere. The integral equation for a hemispherical dielectric-resonator antenna (DRA), excited by either a coaxial probe or a slot aperture, is obtained. The integral equation is solved using the method of moments. The antenna characteristics, such as input impedance, radiation patterns, directivity, and efficiency, are computed numerically, around the resonant frequency of the TE/sub 111/ mode (the HEM/sub 11/ mode for cylindrical coordinates). The computed input impedance is compared with numerical and experimental data available in the literature. >
98 citations
TL;DR: In this paper, a ray-tracing simulation technique is presented to predict path loss and delay spread in urban microcells using simplified geometric-optics assumptions, and the received rays are combined non-coherently as a function of delay.
Abstract: Designers of wireless-communications networks require detailed understanding of radio-propagation in complicated, multi-path channels. Unlike conventional cellular systems, emerging wireless personal-communication networks will most likely operate in confined, urban environments (microcells). The application of broad-band-digital modulation to these networks requires careful consideration of the dispersive nature of the urban radio channel. This paper presents a ray-tracing simulation technique which incorporates site-specific environmental data, such as the location, the orientation, and the electrical properties of buildings, to predict path loss and delay spread in urban microcells. Using simplified geometric-optics assumptions, rays are traced in three dimensions. This determines the paths by which direct, specularly reflected and transmitted, diffusely scattered, and diffracted rays arrive at a receiver. The received rays are combined noncoherently as a function of delay, to estimate the channel power-delay profile. The power-delay profile is used for verification of model accuracy, via qualitative and statistical comparisons of measured and predicted data, for receiver locations on the Virginia Tech campus. The comparisons conclusively show the simulation's ability to accurately model urban microcellular propagation. >
49 citations
TL;DR: In this article, a method for simultaneous tuning of both the resonant frequency and reflection coefficient of a coaxially fed rectangular-microstrip patch is described, where the use of two tuning stubs allows independent adjustment of the effective patch length and the effective position of the feed point.
Abstract: A practical method for the simultaneous tuning, of both the resonant frequency and reflection coefficient, of a coaxially fed rectangular-microstrip patch is described. The use of two tuning stubs allows independent adjustment of the effective patch length and the effective position of the feed point. The effective length determines the resonant frequency of the patch, while the effective position of the feed point determines the input impedance. It is demonstrated that the method allows the adjustment of the feedpoint reflection coefficient of a patch to less than -60 dB, at a frequency which is within 0.005% of specification. >
44 citations
TL;DR: In this article, the types of photonic links and modulator systems available to the antenna engineer are presented, as well as an introduction to the different types of optical modulators.
Abstract: For well over a decade, research groups around the world have been investigating photonic devices for use in antenna, phased-array, and electromagnetic-field-sensor systems. Proposed applications include EMC monitoring, EMP measurements, anechoic-chamber calibration, novel antenna and array designs, remotely located antennas, and smart skins. Photonic antenna links allow immunity from electromagnetic interference, provide an extremely wide working bandwidth, and allow long cable runs with a minimum of loss. Developments in laser technology allow photonic-based links to have very low noise figures and high dynamic range. Opto-electronic devices are now being built in III-V semiconductors (GaAs, InP), which will ultimately lead to opto-electronic integration with MMIC devices. Photonic systems will revolutionize the way in which electromagnetic-measurement and antenna systems will be designed and built in the future. The paper presents an introduction to the types of photonic links and modulator systems available to the antenna engineer. >
37 citations
TL;DR: In this article, the authors proposed a wave-oriented data processing strategy for frequency-domain (FD) and time domain (TD) scattering from periodic and weakly aperiodic arrays.
Abstract: Understanding observable-based observables (OBP) phenomenology should make it possible to link observables, extracted from measured or computed data, to the wave mechanisms from which they originated, aiding in data inversion: we have referred to such a scenario as wave-oriented data processing. Thus, in wave-oriented data processing, one first parameterizes the forward problem in terms of a concise set of observables (forward problem), and then signal-processing algorithms are developed to extract these observables from data (inverse problem). To close the loop, we must show that the data processing algorithms extract wave phenomenology which is consistent with the forward OBP. The authors describe the forward and inverse phases of this strategy in greater detail. A general strategy is then implemented for a very specific scattering problem: frequency-domain (FD) and time domain (TD) scattering from periodic and weakly aperiodic arrays. That scattering problem is described and the results of their previous forward modeling are summarized. The remainder of the article emphasizes inverse, wave-oriented data processing. Processing options for phase-space processing are summarized,and the results for FD and TD scattering are presented. >
36 citations
TL;DR: This article describes a method of using bistatic returns to generate multiple monostatic predictions for each incident angle computed, and shows that the accuracy is initially high, and then degrades as the separation angle between the incident and viewing angles becomes large.
Abstract: Many radar cross section (RCS) prediction codes are limited to one monostatic return per run. However, such codes can calculate multiple bistatic returns per incident angle for a relatively small amount of additional computer resources. This article describes a method of using bistatic returns to generate multiple monostatic predictions for each incident angle computed. Typical results are presented, and show that the accuracy is initially high, and then degrades as the separation angle between the incident and viewing angles becomes large. >
33 citations
TL;DR: Incomplete Lipschitz-Hankel integrals (ILHIs) are a class of special functions that appear in the analytical solutions for numerous canonical problems in electromagnetics as discussed by the authors.
Abstract: Incomplete Lipschitz-Hankel integrals (ILHIs) are a class of special functions that appear in the analytical solutions for numerous canonical problems in electromagnetics. The reason that they appear so often in electromagnetics is because they provide solutions to the wave equation. The intent of the article is to provide an overview of the research that has been carried out in this area. After providing a brief introduction to the theory of ILHIs, applications for these special functions in problems involving diffraction, dispersion, sources radiating in layered media, and traveling-wave sources radiating in a homogeneous space, are discussed. >
29 citations
TL;DR: A target-identification scheme, in which a target in all its aspects to a radar is treated as a pattern class, where a pattern is a set of data features.
Abstract: In the identification of a particular target (or target class), out of a library of possible targets, one can use the scattering signatures from a transient (broadband) type of radar. These signatures are parameter sets (using aspect-independent and/or aspect-dependent parameters) in some scattering model. There are various such models of interest, based on the symmetries (or partial symmetries) of the various target features (geometric shapes, including constitutive parameters), of both local and global varieties. Such symmetries have significance for the signal processing as well, so that the signatures can be better extracted from the noise and clutter background. Based on such symmetries, one can organize the target features, models, signatures, and signal processing into the habitats of a zoo. Part 1 of this article does this. In Part 2, target signatures and pattern recognition are considered. Pattern recognition is a well-established set of techniques for categorizing objects by data features. In the context of radar-target identification, one can use parameters in electromagnetic-scattering models and sets of the same (signatures) for such features. This leads to a target-identification scheme, in which a target in all its aspects to a radar is treated as a pattern class, where a pattern is a set of data features. >
TL;DR: In this article, the authors summarize the historical process which led to recovering the concept of a ray, typical of the pre-Maxwell theory of light, from wave theory, giving evidence to some aspects that led to the formulation of the ondulatory theory of diffraction.
Abstract: The aim of this article is to summarize the historical process which led to recovering the concept of a ray, typical of the pre-Maxwell theory of light, from wave theory. To this end, the contributions of Huygens (1690), Newton (1704), Young (1801), and Fresnel (1816), which can be considered the founders of the modern science of optics, are briefly described, giving evidence to some aspects that led to the formulation of the ondulatory theory of light. Then, it is seen how the concept of a ray was recovered from Kirchhoff's diffraction theory, which can be interpreted as a rigorous formulation of Fresnel's ideas. The key role of the Maggi-Rubinowicz (1888, 1924) representation of Kirchhoff's diffraction integral, which can be interpreted as the mathematical expression of Young's theory of diffraction, is discussed. Also, it is noted that the first theoretical derivation of diffracted rays, and of the cone of diffraction, was due to Adalbert Rubinowicz (1917). He was one of Sommerfeld's assistants, in Munich, in analyzing the transmission of a high-frequency field through an aperture in an opaque screen. The ideas which are briefly summarized produced the basis for the statement of the geometrical theory of diffraction. This ray theory, which is the natural extension of geometrical optics (GO), was presented by J.B. Keller, in 1953. >
TL;DR: In this paper, the microstrip-patch antenna serves multiple purposes: the patch radiates energy, acts as a resonant load, and as a feedback network, and is capable of efficiencies which approach conventional non-radiating oscillator designs.
Abstract: The author discusses class-C FET/patch oscillators; in these, the microstrip-patch antenna serves multiple purposes: the patch radiates energy, acts as a resonant load, and as a feedback network. These integrated antenna/oscillators are capable of efficiencies which approach conventional non-radiating oscillator designs. >
TL;DR: In this paper, an overview of the issues related to electromagnetic analysis of power lines has been presented, including some related to the operation of power line, and others related to effects of the power-line electromagnetic environment.
Abstract: Many issues related to electromagnetic analysis of power lines have been raised. These include some related to the operation of power lines, and others related to effects of the power-line electromagnetic environment. Concern about the latter has been responsible for a renewed interest by the media. An overview of these issues is given. When appropriate, the topics are placed in the context of methods commonly used by those trained in the electromagnetics of antennas and propagation. >
TL;DR: The authors begin by giving a superficial discussion of the Kiernan Reentry Measurements Site (KREMS) program, of which MMW is an active participant, and the suite of sensors located there and the system description includes a discussion concerning the transmitter, antenna, receiver, and signal-processing systems.
Abstract: Kwajalein Atoll is home for four high-power instrumentation radars. Of these four radars, the Millimeter-Wave sensor (MMW) is the most technologically advanced, and has the highest resolution. Although originally designed as an adjunct to the ALCOR radar, MMW was built as a stand-alone system. Since its original design, MMW has undergone a number of modifications. These past modifications, along with the current system architecture, are discussed. In addition, the future plans for MMW, as it evolves into an even-more-powerful sensor, are addressed. The authors begin by giving a superficial discussion of the Kiernan Reentry Measurements Site (KREMS) program, of which MMW is an active participant, and the suite of sensors located there. The system description includes a discussion concerning the transmitter, antenna, receiver, and signal-processing systems. >
TL;DR: In this article, the authors show the potential for high-resolution mapping of ocean-surface wind, waves, and currents using six over-the-horizon (OTH-B) air-defense radars.
Abstract: Science stands to benefit from the quarter century of research and development, and $1.5 billion spent by the Air Force, to deploy six over-the-horizon (OTH-B) air-defense radars, now targeted for shutdown. Opportunities for environmental research and services on a grand scale beckon to anyone who can afford to operate and maintain them. Tests show the radars' potential for high-resolution mapping of ocean-surface wind, waves, and currents. >
TL;DR: In this paper, an analysis of the radiation resistance and gain of the full-wave-dipole antenna has been presented, in order to understand more about this antenna's properties and potential applications for exploiting its high gain benefits.
Abstract: The full-wave-dipole antenna is very seldom used in communication systems, and yet this type of antenna offers a very high gain. This is due to the high input impedance for the center-tap feeding-point antenna. The analysis of short-length and half-wavelength dipole antennas has been reported, in great detail previously, in texts. However, an analysis of the full-wave dipole antenna has not been detailed nor reported, either in texts or journals. Such an analysis is very significant, in order to understand more about this antenna's properties and potential applications for exploiting its high-gain benefits. The paper presents an analysis of the radiation resistance and gain of the full-wave-dipole antenna. This involves special integrations in the mathematics. >
TL;DR: In this paper, the antenna-aperture size is chosen to maximize the directivity at the off-boresight-angle, which is half the EOC beamwidth, to overcome the greater atmospheric attenuation at the edge.
Abstract: This contribution is related to two previous articles in this column: one by James Howell (1991), and the other by Theo Cheston (1990). This article has to do with antenna applications such as geosynchronous-satellite antennas illuminating the Earth. For such applications, gain at the edge of the Earth (EOC) should be maximized, to overcome the greater atmospheric attenuation at the edge. This calls for choosing the antenna-aperture size to maximize directivity (gain) at the off-boresight-angle, which is half the EOC beamwidth. >
TL;DR: In this paper, simple approximations to the Bessel functions can be employed, to accurately model the oscillatory behavior of Bessel function integral for both small and intermediate-sized loop antennas.
Abstract: The purpose of this article is to derive approximate formulas for the radiation resistance (R), and the directivity (D) of circular loop antennas. It is shown that simple approximations to the Bessel functions can be employed, to accurately model the oscillatory behavior of the Bessel function integral for both small and intermediate-sized loop antennas. Furthermore, when these approximations are combined with the usual asymptotic contributions to the integral in the case of a large input parameter ka (a=loop radius, a=2/spl pi///spl lambda/) accurate and relatively simple results for R and D can be secured for all loop sizes. Numerical results can, if necessary, be obtained using a simple pocket calculator. >
TL;DR: This issue's EM programmer's column includes two contributions, one of which presents an interesting and extremely simple method for generating an entire 360-degree monostatic radar cross section (RCS) pattern, from a few bistatic RCS data.
Abstract: This issue's EM programmer's column includes two contributions. The first contribution is by Woo, et al., and is Part I of a survey of grid/mesh generators for partial-differential equation solutions. This survey is intended to provide the community with a list of available grid generators. There is no attempt to give an evaluation of the listed software, other than that provided by the holders of the software. The second paper, by Michael Schuh and Alex Woo, presents an interesting and extremely simple method for generating an entire 360-degree monostatic radar cross section (RCS) pattern, from a few bistatic RCS data. As we know, bistatic data are cheap to generate, because there is no need to redo the solution of the integral or wave equation. Only the radiation-integral evaluation must be repeated, for each bistatic angle. For many targets, the backscatter RCS can be approximated rather well from specular bistatic data, even when the angular separation between the incidence and scattering directions is 5 degrees apart. Schuh and Woo describe how this observation is exploited, to reduce the monostatic-pattern computation by a factor of 10 or so. >
TL;DR: The author describes the capabilities and programming aspects of a typical finite-difference time-domain (FDTD) code for scattering and radiation analysis, and several examples are included, along with memory, CPU, and running-time information.
Abstract: The author describes the capabilities and programming aspects of a typical finite-difference time-domain (FDTD) code for scattering and radiation analysis. The major functions of the code are discussed, and several examples are included, along with memory, CPU, and running-time information. FDTD has been around since the 1960s, but its application to complex composite geometries has primarily occurred during the past decade or so. The code described provides a look at the capabilities of modern FDTD codes. >
TL;DR: In this article, a deformable subreflector was designed and implemented to compensate for part of the gravity deformations of the primary reflector of Haystack, a 37m-(120-ft)diameter Cassegrain radio telescope.
Abstract: A deformable subreflector was designed and implemented to compensate for part of the gravity deformations of the primary reflector of Haystack, a 37-m-(120-ft-)diameter Cassegrain radio telescope. This was done to allow it to operate at 100+ GHz, as compared to the 1-to-10 GHz range for which it was originally designed. The design, analysis, construction, testing, and the results of preliminary measurements of performance are presented. The deformable subreflector consists of a fiberglass shell, supported on an aluminum back structure. The homologous components of deformations are compensated for by optimal positioning of the subreflector, which can be displaced axially and laterally, and tilted. The deformation modes of the subreflector compensate for astigmatic deformations of the back structure of the primary, and for part of the symmetric and anti-symmetric components of gravity sag of the panels of the primary reflector. Analyses show that, due to the deformable subreflector, the surface RMS due to gravity has been reduced from 494 mm (19.4 mil) down to 146 mm (5.7 mil), as the antenna travels over its operating range of 15 to 70 degrees elevation. Combining the reduced gravity effects with surface adjustment and thermal errors results in a predicted combined surface error of 250 mm (9.8 mil), at the extremes of the operating range. >
Journal Article•
TL;DR: In this article, the authors provide an overview of the P&band propagation studies supported by the NASA Propagation Program at the Jet Propulsion Laborato~ (JPL).
Abstract: Reference [1] provides an introduction to ~-band propagation studies supported by the NASA Propagation Program at the Jet Propulsion Laborato~ (JPL). Updates of these activities are presented in this article. Recent and [ current P&band propagation efforts are centered around two pace platforms of opportunity, namely, European Space Agency’s (ESA’S) Olympus and NASAS ACTS I satellites. j The U.S. Olympus measurements were carried out by the Virginia Polytechrfic Institute and State University (Virginia Tech) at Blacksburg, VA, from 1991 to 1993. The measurement phase of that experiment ended in early 1993, and the data analysis phase was completed in December 1993. The ACTS propagation campaign began its data collection phase in December 1993 at several north American sites and will continue for two years and may be extended to three or four years.
TL;DR: In this paper, a typical polyrod pattern in the azimuth plane (H-plane), and a quasi-cosec/sup 2/pattern in the elevation plane (E-plane) are described.
Abstract: The polyrod antenna (or the dielectric-rod antenna) has been known for some time. It is used primarily for its simplicity and unique pattern characteristics. The most interesting characteristic of this antenna is that the radiation pattern can be controlled not only by the cross section, dielectric properties, and length, but also by shaping its axis. By shaping the rod axis, various patterns can be obtained, some of them very useful. The antenna described paper has a typical polyrod pattern in the azimuth plane (H-plane), and a quasi-cosec/sup 2/ pattern in the elevation plane (E-plane). >
TL;DR: In this article, the goal of the K/sub a/-band propagation studies at NASA's Jet Propulsion Laboratory (JPL) is to enable the satellite communications industry to combat propagation channel impairments in the k/sup a/a/-band.
Abstract: Recent and current K/sub a/-band propagation efforts are centered around two space platforms of opportunity, namely, the European Space Agency's (ESA's) Olympus,and NASA's ACTS' satellites. The US Olympus measurements were carried out by the Virginia Polytechnic Institute and State University (Virginia Tech) at Blacksburg, VA, from 1991 to 1993. The measurement phase of that experiment ended in early 1993, and the data-analysis phase was completed in December, 1993. The ACTS propagation campaign began its data-collection phase in December, 1993, at several North American sites; it will continue for two years, and may be extended to three or four years. The goal of the K/sub a/-band propagation studies at JPL is to enable the satellite-communications industry to combat propagation channel impairments in the K/sup a/-band. To define the objectives of the experimental campaigns, JPL relied on the views of the users in industry, academia, and government agencies. >
TL;DR: The author gives a personal account of some of the satellite radio communication experiments being carried out in the late 1950s and early 1960s, including the Sputnik series of satellites and the Nora-Alice payloads on the Discovererseries of satellites.
Abstract: The author gives a personal account of some of the satellite radio communication experiments being carried out in the late 1950s and early 1960s. In particular the author mentions the Sputnik series of satellites and the Nora-Alice payloads on the Discoverer series of satellites. The study of the ionosphere is particularly discussed. >
TL;DR: The user determines which crosssections will be used to define the structure for the purposes of the simulation, and the algorithm will segment all the cross-sections using the user defined segment length, and link them longitudinally to form a fully joined gridded geometry in the NEC GW card format.
Abstract: The user determines which crosssections will be used to define the structure for the purposes of the simulation. Each cross-section is divided into curves to which numerical tags are assigned in order to identify related curves in consequtive croas-sections. These are entered into an ASCII input file. The user-defined cross-sections are normally chosen at a point which coincides with abrupt changes in the structure. The SIG program is initiated. A simple text menu is used to control program function, and the normal procedure is to augment the user defined geometry with additional cross-sections. These computer augmented cross-sections are linearly interpo lated curves between user-defined cross-sections. The next step is to generate a segmented NEC geometry file. The algorithm will segment all the cross-sections using the user defined segment length, and link them longitudinally, to form a fully joined gridded geometry in the NEC GW card format.
TL;DR: In this article, the authors focus only on propagation studies related to radio communications; activities in the field of remote sensing are outside the scope of this review and focus on activities after this period.
Abstract: Reviews activities in the field of propagation research, in the 1990s, in Japan. The authors focus only on propagation studies related to radio communications; activities in the field of remote sensing are outside the scope of this review. Since Kagoshima and Shiokawa (1992) included a short review of research activities in this field, in the period from 1989 to 1991, the emphasis of the present review is placed on activities after this period. The list of references consists of only papers written in English, which have appeared in international journals or published proceedings of international conferences. Reflecting the activities of various fields of propagation research in Japan, two-thirds of the review is devoted to propagation studies related to mobile communications, including land-mobile, mobile-satellite, and indoor communications. The rest of the review covers other basic studies, related to propagation through the atmosphere and precipitation. >
TL;DR: The CNET Antenna Laboratory in La Turbie, France as mentioned in this paper developed three main families of software, developed for axisymmetrical antennas and feeds, center- or offset-fed multiple reflector antennas, and arbitrarily shaped radiating structures.
Abstract: The article gives an overview of the research and development activities of the CNET Antenna Laboratory, in La Turbie, France. After a brief introduction to CNET, it describes three main families of software, developed for axisymmetrical antennas and feeds, center- or offset-fed multiple reflector antennas, and arbitrarily shaped radiating structures. A planar-microstrip array, developed in cooperation with the University of Nice, is also discussed. Following a description of the laboratory's test and measurement facilities, the article concludes with a report on the JINA'92 International Symposium on Antennas. >