Showing papers in "IEEE Antennas and Propagation Magazine in 2006"

Theory and measurement of backscattering from RFID tags

Abstract: This paper presents a method for measuring signal backscattering from RFID tags, and for calculating a tag's radar cross section (RCS). We derive a theoretical formula for the RCS of an RFID tag with a minimum-scattering antenna. We describe an experimental measurement technique, which involves using a network analyzer connected to an anechoic chamber with and without the tag. The return loss measured in this way allows us to calculate the backscattered power and to find the tag's RCS. Measurements were performed using an RFID tag operating in the UHF band. To determine whether the tag was turned on, we used an RFID tag tester. The tag's RCS was also calculated theoretically, using electromagnetic simulation software. The theoretical results were found to be in good agreement with experimental data

A Frequency-Selective Wall for Interference Reduction in Wireless Indoor Environments

Abstract: Modifying the indoor wireless physical propagation environment to reduce the interference level was investigated and demonstrated in this research. A common office partition wall (that was in the main propagation path) was transformed into a frequency-selective (FS) wall by attaching a custom-designed band-stop frequency-selective surface (FSS) as a cover on the wall surface. In-situ measurements showed that this frequency-selective wall filtered out signals operating at 5.4-6.0 GHz (IEEE 802.11a) by an additional attenuation of 10-15 dB compared to the unmodified wall, for incident angles ranging from 0deg-55deg in the azimuth plane and 0deg-20deg in the elevation plane. An attenuation of 10-15 dB in signal strength in the stop band is considered to be significant and beneficial in interference reduction, whereas in the pass-band region (such as 1.8 GHz for cellular telephones), signals experienced only marginally more attenuation than that through the unmodified wall. Results also suggest that the interactions between the FSS and the wall surface can be minimized with an appropriate FSS design, which leads to a feasible and practical product solution: frequency-selective wallpapers. In addition, installation issues, such as misalignment of FSS sheets on the wall, were also examined

A new IEEE standard for safety levels with respect to human exposure to radio-frequency radiation

Abstract: The IEEE Standards Association recently formally approved a new IEEE C95.1 "Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz." Official publication of the standard by the IEEE was expected by late 2005, or soon thereafter. The new IEEE standard contains some features of the current ICNIRP guidelines, but it also includes a number of differences. The new IEEE standard is not identical to the ICNIRP guidelines, even for frequencies used in cellular mobile communications and wireless devices and systems. Moreover, the newly approved IEEE standard departs in major ways from its 1991 edition and subsequent amendments

Polarization-agile antennas

Abstract: A polarization-agile antenna is a type of antenna the polarization state of which can be changed dynamically, i.e., it can have either linear (vertical or horizontal) or circular polarization (left hand or right hand), depending on the requirements of its specific application. This special characteristic offers great flexibility for antenna systems, because a single antenna could be used to satisfy the different requirements of several systems. This paper gives a comprehensive review of polarization-agile antennas. The basics of polarization in antennas and polarization-agile antennas are explained. Various examples of recent developments are then provided, and the antenna configurations and design principles are illustrated and discussed. Finally, the future development of polarization-agile antennas for wireless systems is discussed

Transmission and Reception by Ultra-Wideband (UWB) Antennas

Abstract: Broadband antennas are very useful in many applications because they operate over a wide range of frequencies. The objective of this paper is to study the transient responses of various well-known antennas over broad frequency ranges. As such, the phase responses of these antennas as a function of frequency are of great interest. In the ensuing analysis, each antenna is excited by a monocycle pulse. Many antennas show resonant properties, and numerous reflections exist in the antennas' outputs. The first part of this paper deals with ways of converting various resonating antennas to traveling-wave antennas by using resistive loading. Appropriate loading increases the bandwidth of operation of the antennas. However, the drawback is the additional loss in the load applied to the antenna structure, leading to a loss of efficiency to around fifty percent. However, some of the antennas are inherently broadband, up to a 100:1 bandwidth. Hence, the transient responses of these antennas can be used to determine their suitability for wideband applications with a low cutoff frequency. The second part of the paper illustrates the radiation and reception properties of various conventional ultra-wideband (UWB) antennas in the time domain. An antenna's transient response can be used to determine the suitability of the antenna in wideband applications

Patch-antenna miniaturization using recently available ceramic substrates

Abstract: The recent availability of high-contrast, low-loss ceramic materials provides us with possibilities for significant antenna miniaturization. This paper explores the use of low-temperature co-fired-ceramic (LTCC) substrates in producing a miniaturized patch-antenna design. Of particular interest in the design are parameters such as substrate thickness, input impedance, radiation efficiency, and bandwidth due to the high-contrast ceramic. We propose a thick substrate to increase bandwidth. However, the substrate is truncated to mitigate surface-wave loss, with possible texture to provide dielectric-constant control for improved impedance matching. Utilizing these proposed design modifications, a miniaturization factor of more than eight was achieved, with a return-loss half-power bandwidth greater than 9%. Moreover, respectable gain was maintained, given the achieved miniaturization

Fundamental hmrations of small antennas: validation of wheeler's formulas

Abstract: About sixty years ago, Harold A Wheeler published a paper entitled, "Fundamental Limitations of Small Antennas." Wheeler presented formulas that related the antenna radiation Q to the physical volume of the antenna. This paper (1) briefly reviews the history of the fundamental limitations of small antennas, (2) presents Wheeler's formulas in a revised form, and (3) uses the WIPL-D computer code to validate the Wheeler formulas. The goal is to demonstrate that the Wheeler paper did, indeed, address the fundamental limitations of electrically small antennas, and that it is very useful in the understanding and quantification of these limitations

High Power Electromagnetic Radiators: Nonlethal Weapons anod Other Applications [Reviews and Abstracts]

Abstract: ff Weapons and Other Applications by David V. Gini is a recent title in the Electromagnetics Series published by Harvard University Press, under the editorial guidance of Carl E. Baum. The author attempts to accomplish two main goals: 1.) discuss the evolution of high-power electromagnetic (HPEM) radiators, and 2.) to place HPEM radiators into a larger discussion on the development and use of non-lethal weapons (NLW) in today's changing society. Based on the author's extensive experience in the development of HPEM devices, the book is successful in that aspect. In general, the treatment of non-lethal weapons is much less technical, providing a mainly qualitative description of non-HPEM non-lethal weapon technologies and their potential uses.

Optimization of Helical antennas [Antenna Designer's Notebook]

Abstract: Helical antennas have been known for more than half a century, but it seems that reliable design data for helical antennas do not exist in the open literature. This paper points out some inaccurate data about helical antennas, and presents a new set of data related to the optimum design of helical antennas. The antenna's performance is optimized by varying the antenna's geometrical parameters for narrowband and broadband designs. Based on these results, a set of diagrams is provided to enable simple but accurate design of helical antennas above an infinite ground plane. Finally, the results are experimentally verified

An open-boundary quad-ridged guide horn antenna for use as a source in antenna pattern measurement anechoic chambers

Abstract: The present paper introduces a new antenna design to be used in anechoic chambers. When measuring three-dimensional patterns, the receiving antenna in the anechoic chamber must be able to sense the two orthogonal components of the field that exist in the far field. This can be accomplished by mechanically rotating the source horn in the chamber. A better and faster approach is to use a dual-polarized antenna and to electronically switch between polarizations. This new design is a broadband (2-18 GHz) antenna with dual polarization. The antenna is a ridged guide horn. The novel part is that the sides have been omitted. Numerical analysis and measurements show that this open-sided or open-boundary horn provides a better and more stable pattern behavior for the entire band of operation, as well as good directivity for its compact design. The radiation and input parameters of the antenna are analyzed in this paper for the novel design as well as for some of the early prototypes to show some of the ill effects of bounded quad-ridge horn designs for broadband applications. Mechanically, the antenna is built so that it can be mounted onto the shield of an anechoic room without compromising the shield integrity of the chamber.

A mixed-path groundwave field-strength prediction virtual tool for digital radio broadcast systems in medium and short wave bands

Abstract: The emerging digital technologies for the communication bands from LF up to VHF - bands traditionally used by analog radio systems - necessitate revisiting early analytical propagation methods, and urge engineers to develop novel propagation prediction tools. Existing analytical propagation techniques are based on ray-mode approaches and the Millington curve-fitting approach for mixed-path propagation. These have been endorsed and are used in related ITU (formerly, CCIR) recommendations. These techniques are discussed, with characteristic examples produced via a newly introduced MF/HF groundwave propagation prediction virtual tool (GPVT)

Synthetic aperture radar imaging using a unique approach to frequency-modulated continuous-wave radar design

Abstract: Synthetic-aperture-radar (SAR) imaging is an expensive endeavor. It can be difficult for universities, small business, or individuals to experiment with SAR imaging and algorithm development on a low budget. For this reason, a uniquely inexpensive solution to frequency-modulated continuous-wave (FMCW) radar was developed and then utilized as an ultra-low-cost SAR imaging system. This unique approach to FMCW radar used a pair of low-cost Gunn-oscillator-based microwave transceiver modules, known as "Gunnplexers." These transceiver modules had stability and noise problems, causing them to be unsuitable for use in precise FMCW radar applications when just one module was used. In order to overcome this problem, a unique radar solution was developed that used a combination of two transceiver modules to create a precise and inexpensive FMCW radar system, capable of producing SAR imagery on a budget

Antenna Designer's Notebook - Receiving mutual impedance between two normal-mode helical antennas (NMHAs)

Abstract: A new mutual impedance - the receiving mutual impedance - between two normal-mode helical antennas is defined, measured, and theoretically calculated. The variations of the receiving mutual impedance with antenna separation, with frequency, and with excitation source direction are critically investigated. An application of the receiving mutual impedance in direction finding demonstrates its more accurate description of the mutual coupling effect than that using the conventional mutual impedance

An intuitive electromagnetic approach to MIMO communication systems [Wireless Corner]

Abstract: The aim of this paper is to introduce MIMO propagation in a simple and intuitive way, which exalts the role of the laws of electromagnetism in the channel capacity of space-time communication systems. The approach takes advantage of mode expansions in waveguides and spherical-harmonics expansions in free space to clarify the physical limitations in the channel capacity of MIMO systems

Empirical analysis of a 2 x 2 MIMO channel in outdoor-indoor scenarios for BFWA applications

Abstract: The unquestionable advantages of multiple-input multiple-output (MIMO) systems are having a strong influence on the development of new wireless systems, both in wireless local-area networks (WLANs), and in those designed to offer broadband fixed wireless access (BFWA) services in wireless metropolitan-area networks (WMANs). The MIMO channel characterization in different environments and for different operating frequency bands is a crucial factor in the design of new systems and standards, and for adequate planning of existing systems. This article makes two main contributions. First, the experimental characterization of a 2 times 2 MIMO channel at a frequency of 2.4 GHz in a canonical outdoor-indoor scenario is presented. The channel characterization performed includes the analysis of the spatial correlation between the MIMO system subchannels and its impact on the channel capacity. Second, on the basis of the capacity results obtained, a proposal is made for the use of a 2 times 2 MIMO system in outdoor-indoor scenarios for BFWA applications in metropolitan environments. The proposal is based on the experimentally verified hypothesis that the path loss due to building penetration can be practically compensated for by the diversity gain of 2 times 2 systems

A Method of Cross-Polarization Reduction

Abstract: A method for the reduction of cross-polarized radiation is described. The method can be used for various antenna array systems made up of radiating elements with higher cross-polarized radiation. This solution enables numerous possibilities for selecting the position, the spacing, and the excitation coefficient of any array element. It is even possible to use two different linearly polarized arrays that use the same or different polarizations. Two examples are given: a quarter-wave microstrip antenna system operating in two frequency bands, and a suspended patch array

Antenna Miniaturization Using Magnetic-Photonic and Degenerate Band-Edge Crystals

Abstract: Engineered materials, such as new composites and electromagnetic bandgap and periodic structures have been of strong interest in recent years, due to their extraordinary and unique electromagnetic behaviors. This paper discusses how modified materials, inductive/capacitive lumped loads, and magnetic materials/crystals are impacting antenna miniaturization and performance improvements (e.g., bandwidth and gain reduction, multi-functionality, etc.). Dielectric design and texturing for impedance matching has led to significant size reduction and higher-bandwidth low-frequency antennas, for example. The recently introduced magnetic-photonic crystals (MPCs) and double band-edge (DBE) materials, displaying spectral nonreciprocity, are also discussed. Studies of these crystals demonstrated that magnetic-photonic crystals exhibit the interesting phenomena of (a) drastic slowing down of the incoming wave, coupled with (b) significant amplitude growth, while (c) maintaining minimal reflection at the interface with free space. The phenomena are associated with diverging frozen modes that occur around the stationary inflection points within the band diagram. Taking advantage of the frozen-mode phenomena, we demonstrate that individual antenna elements and linear or volumetric arrays embedded within the magnetic-photonic crystal and double band-edge structures allow for antenna sensitivity and gain enhancements

On the design of a single-layer wideband Butler matrix for switched-beam UMTS system applications [Wireless Corner]

Abstract: A Butler matrix (BM) for UMTS applications is presented. The Butler matrix was fabricated by conventional photolithography on a single laminate. The design is compact and complies with the required bandwidth. The design is based on the use of an elliptical coupler with certain geometrical characteristics, and a Lange coupler as a crossover. Furthermore, a design-scaling procedure that produces an N times N Butler matrix by using two (N/2)times(N/2) Butler matrices is given. The presented performance extrapolations clarify the potential and scalability of our approach

A novel lightweight dual-frequency dual-polarized sixteen-element stacked patch microstrip array antenna for soil-moisture and sea-surface-salinity missions

Abstract: The main motivation for this paper is to discuss the development of a novel compact and light-weight dual-frequency, dual linearly polarized, high-efficiency, stacked-patch microstrip-array antenna for use in standalone aircraft-based remote sensing applications. Results from simulation, fabrication, and testing of a sixteen-element stacked-patch array antenna, optimized for an L-band frequency of operation, are presented. The design center frequencies were 1.26 GHz and 1.413 GHz with 10 MHz and 25 MHz bandwidths in each band, respectively. Due to the large number of design parameters and demanding design requirements of beam-efficiency, sidelobe levels, and polarization characteristics, particle-swarm optimization (PSO) and finite-difference time-domain (FDTD) simulations were used for synthesis and analysis. Cancellation techniques, based on symmetry, were applied to the antenna ports, with a custom-built feed network to reduce cross polarization. Simulations and measurement results from a spherical near-field test facility confirmed excellent performance of the array configuration, with a beam efficiency of greater than 90%, isolation better than -35 dB, and cross polarization in the main beam of the array better than -40 dB. From the sixteen-element array simulations and experimental verifications, one of the objectives of the present study is to suggest the possibility of using customized dual-frequency, dual-polarized arrays as potential feeds for reflectors to replace the traditionally used conical horns for future soil-moisture and sea-salinity missions

A multipurpose FDTD-based two dimensional electromagnetic virtual tool

Abstract: A novel, multipurpose, FDTD-based two-dimensional electromagnetic virtual tool has been designed and introduced. A variety of electromagnetic problems, including radio wave indoor/outdoor, urban/rural propagation, electromagnetic compatibility, resonators, closed/open periodic structures, and linear and planar arrays of radiators can be simulated. This paper describes the software and its use in electromagnetics courses

A MATLAB-based transmission-line virtual tool: finite-difference time-domain reflectometer

Abstract: This article introduces a simple virtual tool, TDRMeter, for the investigation and visualization of time-domain pulsed voltage/current, traveling along a terminated finite-length transmission line, without and with faults somewhere between the source and the load. The package can be used as an educational tool in various undergraduate lectures to aid in teaching electromagnetics as well as transmission lines

Solution of large complex problems in computational electromagnetics using higher-order basis in MoM with out-of-core solvers

Abstract: In a recent invited paper in the IEEE Antennas and Propagation Magazine, some of the challenging problems in computational electromagnetics were presented. One of the objectives of this note is to simply point out that challenging to one may be simple to another. This is demonstrated through an example cited in that article. The example chosen is a Vivaldi antenna array. What we discuss here also applies to the other examples presented in that article, but we have chosen the Vivaldi antenna array to help us make our point. It is shown in this short article that a higher-order basis using a surface integral equation a la a PMCHWT (Poggio-Miller-Chu-Harrington-Wu-Tsai) method-of-moments formulation may still be the best weapon that one have in today's arsenal to deal with challenging complex electromagnetic analysis problems. Here, we have used the commercially available code WIPL-D to carry out all the computations using laptop/desktop systems. The second objective of this paper is to present an out-of-core solver. The goal is to demonstrate that an out-of-core 32-bit-system-based solver can be as efficient as a 64-bit in-core solver. This is quite contrary to the popular belief that an out-of-core solver is generally much slower than an in-core solver. This can be significant, as the difference in the cost of a 32-bit system can be 1/30 of a 64-bit system of similar capabilities using current computer architectures. For the 32-bit system, we consider a Pentium 4 system, whereas for the 64-bit system, we consider an Itanium 2 system for comparison. The out-of-core solver can go beyond the 2 GB limitation for a 32-bit system and can be run on ordinary laptop/desktop; hence, we can simultaneously have a much lower hardware investment while better performance for a sophisticated and powerful electromagnetic solver. The system resources and the CPU times are also outlined.

Electric-line-source illumination of a circular cylinder of lossless double-negative material: an investigation of near field, directivity, and radiation resistance

Abstract: his work investigates the properties of an antenna-like configuration with an electric line source radiating in the presence of a double-negative circular cylinder. First, the analytical eigenfunction-series solution is derived. Second, this solution is employed in numerical calculations to study the properties of the near field, inside as well as outside the cylinder, and the far-field. Third, the variations of these fields are examined, as well as the radiation resistance and radiation pattern, as functions of the geometrical and electromagnetic parameters of the configuration. It is demonstrated that the scattering properties of the double-negative cylinder are vastly different from those of the corresponding double-positive cylinder. In particular, the focusing effect inside the cylinder and the angular variation of the directivity exhibit distinct characteristics

Bandwidth Optimization of an Integrated Microstrip Circulator and Antenna Assembly: Part 2

Abstract: The integration of a ferrite circulator with an arbitrary load - such as a wideband antenna - is considered by examining the conditions for perfect circulation over large bandwidths. These conditions relax the requirements of the loading impedance from being purely real (e.g., 50 ohms) to being complex, per a circulation impedance equation. The impedance equation is couched in terms of open-circuit impedance parameters, which are the natural parameters for describing an embedded microstrip circulator. By means of a rigorous field analysis, the impedance parameters are computed by modeling the microstrip ferrite circuit as a closed PEC/PMC cavity. The justification, features, and limitations of this model are discussed in detail, it is shown herein how the Z parameters can be invoked in some search algorithm to optimize the parameters of the ferrite, to achieve either superb circulator bandwidth or isolation performance. An example of a wideband circulator is given for which both simulation and experimental data are provided. The high degree of correlation between these two data sets corroborates the methodology

Wireless Sensor Motes for Small Satellite Applications

Abstract: Motes are low-cost COTS (commercial off-the-shelf) microchips, which integrate a processor, onboard sensor, RF communications link, and a power unit. High levels of power efficiency can be achieved with the use of the IEEE 802.15.4 protocol for communication between the motes, allowing long-term periods of operation for motes and reducing the power requirements of a spacecraft. The article examines the feasibility of using sensors for harness reduction between satellite subsystems, and for inter-satellite networking capabilities between satellite swarms

Powering autonomous cubic-millimeter devices

Abstract: The reported results are concerned with powering miniature autonomous devices using radio-frequency (RF) energy, not requiring batteries or wires. The century-old concept of transmitting energy using RF is now practical for numerous applications. The method of evaluating the receiving area of miniature antennas is presented, and implemented using a particular antenna profile with inherent electrical inductance and capacitance properties. The research demonstrates the ability to obtain the theoretical antenna effective area. The results facilitate the economical fabrication of an antenna as an integral part of a printed circuit board or complementary metal-oxide-semiconductor (CMOS) device

Application of the method of least to electromagnetic engineering problems

Abstract: In this paper, a brief review of the application of the method of least squares (MLS) to electromagnetic engineering problems is presented. By describing the analysis, design, synthesis, and optimization of several antenna and microwave components and devices, the capabilities and power of the MLS for tackling such problems are amply illustrated. The MLS may also be used for the computation of some propagation problems. First, as an introduction to the MLS, its application is presented for some common problems in engineering mathematics, such as the solution of equations (transcendental equations, polynomials, systems of linear and nonlinear equations, etc.), curve fitting of some set of functions to known measurement data, and the determination of Fourier-series coefficients. Next, some specific electromagnetic engineering problems are briefly presented, such as electrostatic problems, the solution of linear operator equations, the solution of integral equations, the solution of differential and integro-differential equations under some specified boundary conditions, the description and application of the least-square boundary residual method (LSBRM) (for the solution of the junction of cylindrical waveguides; E-plane metallic strips, both free-standing and on a dielectric slab in rectangular waveguides; etc.), the optimum design of impedance transformers, multi-hole directional couplers, coupled-line, branch-line, and microstrip couplers, coupled-line filters, a Wilkinson power divider, the analysis of wire antennas, slot antennas, ring antennas, and the optimum design of a slot antenna profile. The main theme of the paper is to convey the methods of construction of error functions by the MLS for the analysis or optimum design of the devices used as examples

A novel virtual FDTD-based microstrip circuit design and analysis tool [Education Column]

Abstract: A novel FDTD-based virtual education/research tool is introduced, and characteristic examples are presented. The beauty of this tool comes from its visualization power, as well as easy-to-use design steps. The tool can be used effectively in microstrip circuit analysis and design problems

A commercial perspective on the development and integration of an 802.11a/b/g hiperlan/WLAN antenna into laptop computers

Abstract: Commercial antenna design for wireless applications involves a significant number of tradeoffs with other competing engineering requirements The design of an 80211 a/b/g HiperLan/WLAN antenna into a laptop computer is used to illustrate one path taken to produce a commercially successful dual-band antenna design The candidate design chosen was a stacked dual-slot configuration, driven with a microstrip line across both slots and shorted at appropriate edges Coaxial cable was connected to the center of the antenna The upper slot was shown to have a second fundamental resonance, which precluded a good match at 49 GHz with the high-frequency slot This slot was truncated at its center to eliminate the undesired resonance and to allow the lowest resonance to remain intact, which, in turn, allowed for a good match at 49 GHz The high-frequency slot was then optimized to create a fundamental and a second "fictitious" resonance, which allowed one to create a large impedance bandwidth, as required The measured impedance, isolation, and gain results for an antenna integrated into a laptop are presented

Calculated thermal behavior of ventilated high precision radio telescopes

Abstract: Radio telescopes that operate at millimeter and sub-millimeter wavelengths need a reflector-surface precision of a few tens of microns and a pointing accuracy of a few arcseconds. When built in a conventional way from steel and aluminum, as in the case of larger-diameter telescopes, thermal control must be applied to reduce temperature-induced deformations, in particular of the reflector backup structure. We illustrate that it is possible to make model calculations - for instance, during the design phase - that simulate the thermal behavior and the operation of a telescope when servo-loop-controlled ventilation or climatization (air-conditioned ventilation) of the backup structure is applied. We explain the technique of model calculations, and present as an example the calculated thermal behavior of a ventilated 64-m-diameter telescope and of the climatized 30-m IRAM telescope. It is explained that the thermal control of a telescope mount is less demanding if frequent pointing corrections can be made