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Extensive analysis of wire antennas using method of moments (MoM) has been performed over the past decades. Despite the thorough understanding and widespread use of the wire antennas, higher order modeling of wire structures has received little to no attention over the years. This may be because the inaccuracies associated with the classic reduced kernel approach used to analyze wire antennas have precluded the use of higher order basis functions. This paper combines a new method for computing integrating the cylindrical wire kernel with higher order basis functions for the accurate modeling of wire antennas. Numerical results demonstrate the higher order convergence of the approach. Index Terms--Cylindrical kernel, cylindrical wire antennas, higher order modeling, method of moments (MoM).

A novel dual-band printed loop antenna very promising for application in mobile phones as an internal antenna is presented. The antenna comprises an outer loop strip and an inner inverted-L strip connected to and enclosed by the outer loop strip. The antenna occupies a compact area of 15 x 50 [mm.sup.2] only, yet generating three resonant modes to form two wide bands at about 900 and 1800 MHz for the Global System for Mobile Communication/Digital Communication System operation. Detailed design considerations of the three excited modes are described in the paper. When a shielding metal case is placed close to the antenna, small effects on the antenna's impedance matching are seen, allowing compact integration of the antenna with nearby conducting elements or electronic components. The antenna is also found to result in small excited surface current distributions on the system ground plane of the mobile phone. This behavior is expected to lead to reduced user's hand effects on the radiation efficiency of the antenna. Index Terms--Dual-band antennas, mobile phone antennas, printed antennas, printed loop antennas.

A new approach for multiport network modeling (MNM) of multilayer planar circuits coupled through slots in ground plane is introduced. Generalized network formulation for aperture problems is combined with Okoshi's model for planar circuits to obtain a unified circuit model for two irregularly shaped planar circuits coupled through a slot of arbitrary shape in their common ground plane. The methodology, which can be generalized to structures having more than two layers, is described by applying the method to a two-layer structure. Results for several sample structures will also be presented. Index Terms--Complex images, generalized admittance matrix, Green's functions, multiport network modeling (MNM), planar circuits.

Large parabola dish antennae are in use for station-to-satellite communications, satellite tracking for precise orbit determination, very long baseline interferometry, and others. In this paper a procedure for the precise determination of the satellite tracking antenna reference point (ARP) position in the International Terrestrial Reference Frame is outlined. It is based on measurements made directly to the rotatable elevation housing of the antenna in various azimuth and elevation positions. The three-dimensional position of both rotation axes are obtained from the calculation of best-fitting circles. The resulting ARP is tied into a local geodetic network around the antenna to be observed by global positioning system (GPS) in combination with terrestrial measurements using a 3D data integration model including geoidal heights. ITRF coordinates are determined by static GPS observations using the products of the International Global Navigation Satellite Systems Service. Results are shown exemplarily for two European Space Agency antennae. The ARP was determined in both cases with a coordinate accuracy of approximately 5 mm. A description of the procedures, including terrestrial measurements, data evaluation models, and quality assessment is given. DOI: 10.1061/(ASCE)0733-9453(2007)133:2(41) CE Database subject headings: Geodetic surveys; Global positioning; Parameters.

Magnetically insulated line oscillator (MILO) is a gigawatt-class high-power microwave source whose behavior has been investigated experimentally and numerically. This paper presents an improved MILO model. A novel beam dump, a one-cavity RF choke section and a novel mode-transducing antenna are introduced into the improved MILO. The improved MILO is investigated in detail with particle-in-cell method (KARAT code). In simulation, high-power microwave of transmission electron microscopy (TEM) mode is generated with peak power of 4.2 GW, frequency of 1.76 GHz, and peak power conversion efficiency of 12%, when the voltage is 600 kV and the current is 52 kA. A novel plate-inserted mode-transducing antenna, which is composed of a plate-inserted mode converter and a coaxial horn, is introduced into the improved MILO. The TEM wave generated by the MILO propagates down the section of coaxial waveguide and is transformed into the TEll mode by the novel plate-inserted mode converter, and then radiated by the coaxial horn antenna into air. The direction of the radiated microwave agrees with the axis of the MILO. Index Terms--Crossed field devices, high-power microwave source, magnetically insulated line oscillator (MILO), mode-transducing antenna, particle-in-cell (PIC) method.

This paper is focused on using plasma as a substitute for metal in a frequency selective surface ('FSS'). FSSs have been used for filtering electromagnetic waves. Each FSS layer has to be modeled using numerical methods, and the layers are stacked in such a way to create the desired filtering. Genetic algorithms are used to determine the stacking needed for the desired filtering. This is a complicated and numerically expensive process. We developed a method to replace metal in an FSS with plasma elements. Our plasma FSSs can be tuned to a desired filtering by varying the density in the plasma elements. This could save much of the routine analysis involved in the standard analysis of the conventional FSS structures. The user simply tunes the plasma to get the desired filtering. Plasma elements offer the possibility of improved shielding along with reconfigurability and stealth. Plasma FSS can be made transparent by turning the plasma OFF. This extends our previous scientific achievements in the development of the plasma antenna. Index Terms--Active antennas, antennas, plasma antennas, plasma devices.

Parametric study of ultrawideband printed elliptical monopole antennas have been presented. Design curve for the length of the feed transmission line for various lower band edge frequencies has been generated. Variation of bandwidth with ellipticity ratio of these configurations has also been studied. Experiments have been performed to measure bandwidth and radiation patterns of these configurations, which tally well with simulated results. The elliptical configuration with ellipticity ratio of 1.1 gives ultrawide impedance bandwidth ratio of 12.4:1 as compared to 10.2:1 of the circular monopole antenna. This antenna introduces minimum ringing and distortion/dispersion of the pulse in time domain. Index Terms--Printed elliptical monopole antenna, ultrawideband (UWB) technology.

Amplitude weighting at the subarray outputs alone causes grating lobes in array factors. An approach that disrupts the periodic quantization by dividing the array into subarrays of unequal sizes and amplitude weighting at the subarray ports is presented. A hybrid genetic algorithm optimizes the subarray size and subarray weights to minimize the maximum sidelobe level. Index Terms--Antenna arrays, genetic algorithms (GAs), linear arrays, phased arrays, subarray feeds.

A wideband U-shaped parasitic patch antenna is proposed. Two parasitic elements are incorporated into the radiating edges of a rectangular patch whose length and width are [[lambda].sub.g]/2 and [[lambda].sub.g]/4, respectively, in order to achieve wide bandwidth with relatively small size. Coupling between the main patch and U-shaped parasitic patches is realized by either horizontal or vertical gaps. These gaps are found to be the main factors of the wideband impedance matching. The proposed antenna is designed and fabricated on a small size ground plane (25 mm x 30 mm) for application of compact transceivers. The fabricated antenna on a FR4 substrate shows an impedance bandwidth of 27.3% (1.5 GHz) at 5.5 GHz center frequency. The measured radiation patterns are similar to those of a conventional patch antenna with slightly higher gains of 6.4 dB and 5.2 dB at each resonant frequency. Index Terms--Parasitic patch antenna, U-shaped parasitic patches, wide bandwidth.

A compact ultrawideband (UWB) antenna has been designed for UWB cancer detection systems. The numerical analysis and experimental characterization of a printed monopole antenna fed by a 50-[ohm] coplanar waveguide (CPW) and operating in a lossy coupling medium is presented. A detailed 3D model of the antenna and the biological environment has been constructed and simulated in XFDTD and HFSS. The near-field pattern of the antenna in the proximity of a multilayer human body model and the effect of the human body on the input matching of the antenna are studied. Experimental results show that the return loss is below -9.6 dB from 3.4 GHz to 9.9 GHz. Index Terms--Coplanar waveguide, ultrawideband (UWB) antenna, ultrawideband (UWB) imaging.

The problem of synthesizing 'optimal' sum and difference patterns subject to arbitrary sidelobe bounds by means of a simple feeding network is dealt with. It is shown how a hybrid optimization procedure properly acting on both clustering into subarrays and excitations of these latter greatly improves performances of known feeding architectures with respect to existing procedures. Results of the proposed technique, which significantly outperform existing methods, renew the interest of these simple feeding architectures, and emphasize the effectiveness of this kind of hybrid procedures exploiting the convexity of the problem with respect to a part of the unknowns. Index Terms--Antenna arrays, convex programming (CP), hybrid optimization, monopulse antennas, sum and difference patterns.

A novel, ultrawideband (UWB) monopole antenna suitable to be mounted on the printed circuit board (PCB) of a wireless, universal, serial-bus (USB) dongle as an internal antenna is presented. The proposed antenna in the study is a U-shaped, metal-plate monopole antenna, easily fabricated from bending a simple metal plate onto a foam base of a compact size of 6 x 11 x 20 [mm.sup.3]. The antenna mainly comprises a pair of wide-ended radiating arms and a bevel-feed transition. When the antenna is mounted at the top portion of the PCB, one end of the radiating arm is also short-circuited to the system ground plane. With the proposed antenna structure, which can provide a very wide operating bandwidth of larger than 7.6 GHz, the antenna impedance bandwidth can easily cover the 3.1-10.6 GHz UWB band. Details of the antenna design are described, and experimental results of the constructed prototypes are presented and discussed. Index Terms--Antennas, internal antennas, ultrawideband (UWB) antennas, universal serial-bus (USB) dongle antennas.

The performance of multiple-input multiple-output (MIMO) systems using beam selection is investigated in this paper. Based on the results of a channel sounding campaign carried out at the University of Manitoba for line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios, it was possible to contrast the results of transmitter, receiver and joint beam selection in rich scattering environments. The channel was characterized in the 1-2.4 GHz frequency band with a multipath delay resolution better than 5.8 ns. The beam selection was performed by exhaustive search method. The results led us to important conclusions regarding the beam selection procedure and its potential to improve the indoor channel capacity. In LOS, the single input single output (SISO) system that favours the maximum power direction of arrival (DOA) maximizes the capacity. Capacity improvements are observed by increasing the number of receiver beams (RBs) only at high signal-to-noise ratios (SNRs) for omnidirectional transmission. The best performance in transmitter beam selection in LOS is observed by increasing the number of transmitter beams (TBs) for high SNRs. In the case of NLOS, the capacity performance is improved when more than a single beam is used in either, transmitter or receiver side. The joint transmitter-receiver beam selection exhibits best capacity performance only for large SNRs in LOS while the SISO systems outperforms any joint beam selection alternative for low SNRs. In contrast, in NLOS environments, the use of joint beam selection shows a constant capacity performance improvement starting from lower SNR than in the LOS case. Index Terms--Information rate, multiple-input multiple-output (MIMO) systems, multibeam antennas, multipath channels, time-domain measurements.

A thin dual-band internal patch antenna for Global System for Mobile Communication, 890-960 MHz/Digital Communication System, 1710-1880 MHz (GSM/DCS) operation in a Personal Digital Assistant (PDA) phone is presented. The antenna can generate two wide resonant modes for GSM (890-960 MHz) and DCS (1710-1880 MHz) operation, yet it requires an air-layer substrate of thickness 4 mm only, which is among the thinnest internal mobile phone antennas that have been reported. The antenna's top patch comprises a resonant narrow strip supporting a longer resonant path for GSM operation and a resonant subpatch supporting a shorter resonant path for DCS operation. By including a suitable widened end portion for the narrow strip and a suitable tapered end portion for the subpatch, increased bandwidths for the proposed thin internal mobile phone antenna are obtained. Detailed design considerations of the proposed antenna are described. In addition, the user's hand effects on the performances of the proposed antenna are studied. Index Terms-GSM/DCS mobile phone antennas, internal antennas, internal mobile phone antennas, mobile antennas.

The benefits resulting from the inclusion of ferrite in material loaded antennas are investigated, initially through the use of a spherical analytic model and then through a transmission line matrix simulation tool applied to a rectangular slab geometry. It is observed that a material with equality of relative permittivity and permeability in combination with specific positioning of the antenna in relation to the head, can result in the definitive small-size, high efficiency and bandwidth, low specific absorption rate (SAR) antenna. The accuracy of the simulations is validated both through efficiency and SAR measurements of three material coated monopole samples. Further research into optimizing the above attributes and translating them into a handset antenna leads to a multiband antenna design covering the GSM 1800, 1900, UMTS and Bluetooth bands, with a SAR value reduced by 88% compared to conventional phones and an efficiency of 38% at 1.8 GHz. A tri-band antenna design is also presented, utilizing currently available lossy ferrite material and it is considered as the first step towards the feasibility of the ultimate low SAR multiband ferrite handset antenna, until further material development specifically for antenna applications takes place. Index Terms--Ferrite loaded antennas, multiband, specific absorption rate (SAR), wireless handset.

A set of antenna-optimization problems is presented that satisfies the necessary requirements to form a test suite useful for measuring and comparing the performance of different evolutionary optimization algorithms (EAs) when they are applied to solve complex electromagnetic problems. The ability of the proposed test suite to find strong and weak points of any EA is illustrated by a complete study of four broadly used evolutionary algorithms carried out with the aid of the new test functions. Index Terms--Antennas, genetic algorithms (GAs), optimization methods, particle swarm.

A new and efficient integral equation approach is presented to model heterogeneous dielectric volumes in a multilayered environment. The dielectric volumes can be vertically large, they can cross dielectric interfaces and they should be 'quasi 3-D' which means that the contour faces should be placed either horizontally or vertically in the multilayered environment. In this way, a perpendicular prismatic mesh can be fitted on the volumes and the 3-D displacement currents can be expanded in generalized rooftop functions with separated horizontal x, y- and vertical z-dependencies. This makes it possible to evaluate all z, z' reaction integrals fully analytically in the spectral domain and ensures an efficient implementation. The formulation of the source-field relations is adapted to the quasi 3-D geometries as a hybrid dyadic-mixed potential form. Additionally, the electromagnetic coupling between dielectric volumes and metal sheets is included using a coupled volume/surface formulation. This turns the implementation into a complete full wave solver for planar antennas containing both finite and infinite dielectric regions. In order to illustrate and validate the presented approach, two patch antennas with a local volumetric inhomogeneity under the patch are numerically analyzed in a multilayered environment. Eventually, a matrix fill time comparison is used to demonstrate the improvement in computation efficiency. Index Terms--Heterogeneous dielectric volumes, method of moments (MoM), multilayered Green's function, surface integral equations (SIE), volume integral equations (VIE).

The effect of multilayer geometry on microstrip antennas is investigated for the design of antenna-integrated mechanical structure. Changes in the gain of antenna due to the geometry have been determined using a transmission line analogy. Design of high-gain antenna in bandwidth is proposed away from structural resonance. Experiments are done on microstrip antennas covered by superstrates in order to verify high-gain conditions theoretically derived herein. The off-resonant conditions that use practical materials of moderate thickness make it possible to design the antenna-integrated mechanical structure with the perfect integration of high mechanical and electrical performances. Index Terms--Composite structure, embedded antenna, gain enhancement, integrated antenna, mechanical structure.

A 3-D fractal-tree monopole antenna was realized using electrochemical deposition technique. Experimental results on the return loss over the band 1-20 GHz and radiation patterns at all resonating frequencies were presented. The multiband electromagnetic behavior of the antenna was studied and compared to a previously reported 2-D fractal-tree antenna studied by C. Puente et al. It is shown that the impedance bandwidth of the 3-D structure were improved compared to the reported 2-D structure with less dense band distribution. The resonating bands of the fractal structure are related to the length distribution over the fractal shape. Results for the 3-D fractal-tree antenna structure show the expected self-similar behavior. Index Terms--Antennas, fractal tree antenna, fractals, multi-frequency antennas.

Integrated lens antennas (ILAs) are essentially high-gain (sub)millimeter-wave radiating structures. They often have a moderate (or even poor) aperture efficiency because their design rules are generally based on high-frequency methods of analysis with no advanced optimization procedures. From the proposed classification of ILA types as a function of their aperture efficiency, we demonstrate the feasibility of designing compact arbitrarily-shaped ILAs with high radiation and aperture efficiencies, which has never been addressed to our best knowledge. The design strategy consists of a local iterative optimization of trial lens shapes that are analyzed with a spherical wave expansion (SWE) of the primary fields and the physical optics (PO) method. This approach assumes that the feed currents are not modified by the irregular lens profile and the dielectric contrast at the lens interface; in addition, the influence of internal reflections and possible indirect paths is neglected. The proposed methodology is thus restricted to the optimization of low-permittivity lenses. The SWE/PO algorithms and the gradient-based optimization procedures are validated numerically in Q-band by considering two peculiar ILAs. The first example (designed and characterized experimentally in a previous contribution) is used as a relevant test-case in order to validate the method of analysis. The second prototype is a Teflon compact shaped ILA whose diameter and height equal 1.8 x [[lambda].sub.0] and 1.5 x [[lambda].sub.0], respectively. This antenna is shown to have a 92% aperture efficiency and a 70% radiation efficiency. Although purely numerical, these data are among the highest values reported in literature. They are confirmed by FDTD simulations. Index Terms--Compact shaped dielectric lens, integrated lens antennas (ILAs), local optimization, millimeter wave, shaped beam, spherical mode expansion.

Reflector antennas with complex mesh weave patterns are numerically analyzed by using extended physical optics (PO) combined with the periodic method of moments (MoM). The method applies the periodic MoM with Rao-Wilton-Glisson (RWG) basis and testing functions. It calculates the transmission coefficient matrix (T-matrix) of the realistic, complex weave pattern of the planar mesh, in order to calculate the modified PO current on the mesh reflector. When analyzed, the planar grid mesh is found to be compatible with the commonly used wire-grid model. The modified PO current on the locally planar mesh is implemented on the curved reflector surface for the diffraction analysis of the mesh reflector antennas. The far-field pattern of the offset parabolic antenna with grid mesh, modelled using periodic MoM, agreed well with those obtained from the wire-grid model. T-matrix calculated from the tabulated T-matrix data using the interpolation method is sufficiently accurate and compares well with the one calculated using the direct method, allowing users to choose one of the T-matrix calculation methods depending on the problem. The analysis of the mesh reflectors with two different complex weave patterns (single Satin and single Atlas at Ka band) is performed to exemplify the application of the extended PO/periodic MoM algorithm. It is shown that differences were observed in cross-polarization discrimination (XPD) for circular polarization operations depending on the weave patterns. This result demonstrates the usefulness of the proposed technique in accurate performance prediction of mesh reflector antennas with complex weave patterns. Index Terms--Mesh reflecting surfaces, periodic method of moments, physical optics, reflector antenna, spaceborne antenna.

Exploring the vast search space of possible wire antenna designs is a task well suited for genetic algorithms. Many of the current implementations use a direct mapping between genome and antenna feature, or evolve drawing instructions. We explore the evolution of antennas using a growth process. The design of wire antennas for communication applications demonstrates the feasibility of this approach. Index Terms--Electromagnetic optimization, genetic algorithms (GAs), wire antennas.

Concatenation of orthogonal space-time block codes (OSTBC) with an outer trellis has led to simple and powerful codes, known as superorthogonal codes or space-time block trellis-coded modulation. In this letter, we generalize these codes by finding new code supersets and corresponding set partitioning, resulting in improved coding gain. We provide design guidelines for the labeling of the generalized code trellises and demonstrate the gains by several example designs for two and four transmit antennas. Index Terms--Multiple-input multiple-output (MIMO), spacetime coding, superorthogonal codes.

In marked contrast with the ideal error-free feedback assumption that is common in the literature, practical systems are likely to have severely bandwidth-limited, error-prone feedback channels. We consider the scenario where feedback from the receiver is used by the transmitter to select the best antenna, out of many available antennas, for data transmission. Feedback errors cause the transmitter to select an antenna different from the one signaled by the receiver. We show that optimizing the signaling assignment, which maps the antenna indices to the feedback codewords, improves performance without introducing any additional redundancy. For a system that uses error-prone feedback to transmit quadrature-phase-shift-keying-modulated data from a single antenna selected from many available spatially correlated antennas, we derive closed-form approximations for the data symbol error probability for an arbitrary number of receive antennas. We use these to systematically find the optimal signaling assignments using a low-complexity algorithm. The optimal signaling is intimately coupled to how the receiver performs selection verification, i.e., how it decodes the data signal when, due to feedback errors, it does not always know which antenna was used for data transmission. We show that ignoring feedback errors at the receiver can lead to an unacceptable performance degradation, and develop optimal and sub-optimal, blind and nonblind selection-verification methods. With a small side-information overhead, nonblind verification approaches the ideal perfect selection-verification performance. Index Terms--Antenna arrays, antenna selection, combinatorial optimization, detection, diversity reception, maximum a posteriori (MAP) estimation, multiple-input multiple-output (MIMO) systems, radio receivers, receiving antennas, selection verification, spatial correlation, transmitting antennas.

This paper describes the realization of a low-temperature co-fired ceramic (LTCC)-based wireless transceiver with optical interface for radio-over-fiber applications involving several standards. The RF front-end including an antenna is fabricated in LTCC technology, while the optical transceiver with a single-mode optical interface is built on a silicon motherboard. The front-end operates in the 5-6-GHz band, while the modulated optical carrier is transmitted at 1.55-[micro]m wavelength. The front-end module is an attractive solution for wireless local area network applications such as IEEE 802.11a or HIPERLAN2 requiring a direct link to an optical backbone. Index Terms--Low-temperature co-fired ceramic (LTCC), optically fed antennas, opto-electronics, radio-over-fiber, transceiver, wireless local area network (WLAN).

This paper discusses the reconstruction of the subsurface from radar data using a time-domain reconstruction method. Before the reconstruction is conducted, data preprocessing is carried out. The preprocessing transforms measured data transmitted and received by 3-D dipole antennas into equivalent data excited and received by 3-D ideal electric dipoles and, then, into equivalent data excited and received by 2-D ideal electric dipoles. Distributions of permittivity, conductivity, and permeability are reconstructed from the preprocessed data by a 2-D forward--backward time-stepping waveform inverse scattering technique. Two 2-D examples of permittivity and conductivity reconstruction from synthetic noisy and field borehole radar data are demonstrated to show the effectiveness of the proposed method. Index Terms--Antenna transformation, borehole radar, dipole antenna, ideal electric dipole, waveform inverse scattering.

The detection of antipersonnel landmines using ground-penetrating radar (GPR) is particularly hindered by the predominant soil surface and antenna reflections. In this paper, we propose a novel approach to filter out these effects from 2-D off-ground monostatic GPR data by adapting and combining the radar antenna subsurface model of Lambot et al. with phase-shift migration. First, the antenna multiple reflections originating from the antenna itself and from the interaction between the antenna and the ground are removed using linear transfer functions. Second, a simulated Green's function accounting for the surface reflection is subtracted. The Green's function is derived from the estimated soil surface dielectric permittivity using full-wave inversion of the radar signal for a measurement taken in a local landmine-free area. Third, off-ground phase-shift migration is performed on the 2-D data to filter the effect of the antenna radiation pattern. We validate the approach in laboratory conditions for four differently detectable landmines embedded in a sandy soil. Compared to traditional background subtraction, this new filtering method permits a better differentiation of the landmine and estimation of its depth and geometrical properties. This is particularly beneficial for the detection of landmines in low-contrast conditions. Index Terms--Clutter reduction, ground-penetrating radar (GPR), inverse modeling, landmine detection, phase-shift migration.

This letter presents two results for antenna selection under keyhole condition. First, we analyze the capacity of the antenna-selection keyhole channel. We show that in an M x N system a small number of selected antennas can match the capacity of a baseline full-antenna system (baseline system has no feedback). Second, we formally prove the intuitive result, until now unproven, that antenna selection in the keyhole multiple-input multiple-output channel preserves the available diversity of the channel. Index Terms--Antenna selection, capacity, diversity order, keyhole channel.

The impedance change that occurs when the user holds a mobile phone antenna is a well-known problem. This paper analyses the contributions to this change for a dual-band PIFA. In particular, the contribution of the slot is shown and a method of reducing it is proposed and analyzed. Index Terms--Antenna, impedance, interaction, planar inverted F antenna (PIFA).

This paper investigates the problem of estimating the position of a scanning emitter using a passive scan-based geolocation technique. This is achieved by taking advantage of the geometric constraints introduced by the uniform rotating motion of the antenna main beam as it sweeps across a number of separate receivers. A detailed analysis of the estimation process and accuracy of the emitter position is given and a number of computer simulations showing the benefits of this geolocation technique are also included.

Abstract--In this paper, we consider the analysis of the acquisition process for a hybrid double-dwell system with antenna diversity for DS-CDMA (direct sequence-code division multiple access) using an adaptive threshold. [...]

On-body propagation channel measurements using two microstrip patch antennas for various links are presented and statistically analyzed. The attenuation attributed to factors such as the body, head and clothing are: 19.2, 13.0, and 1.7 dB, respectively, when measurement performed in the anechoic chamber. Measured cumulative distribution function (CDF) of data in the chamber and lab fits to lognormal distribution with deviation factors comparable in both cases. The results demonstrate that the human body is a major shadowing contributor in body area network (BAN) radio systems. The performance of potential radio systems under the measured channel variations is also investigated. Excellent system performance is achievable with power levels as low as 0.01 mW. These results support the significance of channel characterization and modelling in producing suitable wireless systems for ultra low power BANs. Index Terms--Bit error rate (BER), body area network, microstrip antenna, on-body propagation.

Two new designs of dual frequency coplanar waveguide (CPW)-fed double folded slot antennas are presented. An important advantage of these antennas is that they are self-matched to the feeding CPW without the need for external matching circuit. This reduces the antenna size and simplifies its design. To verify the designs, the return loss and radiation patterns are measured and compared to those obtained using available commercial software with good agreement. Index Terms--Coplanar waveguide (CPW), multiple band antennas, slot antennas.

A novel ultrawideband planar gap-loaded folded antenna is proposed in this paper, which is derived from an ordinary three-wire folded antenna with the gap-loading technique. The fabricated monopole antenna has a small electrical size and a measured bandwidth of 8.8:1 ranging from 1.48 to 13 GHz. The operating principles of the proposed antenna, including the excitation of three main resonant modes and their effects on the return loss, are analyzed. The proposed antenna exhibits a relatively stable radiation pattern, as proved experimentally in the paper. In the end, the parametric studies are performed for practical applications. Index Terms--Broadband antenna, folded antenna, gap loading, planar antenna.

A new class of miniature printed embedded inverted-F antennas are proposed for operation in the 2.4-2.485 GHz wireless local-area network band. One of the proposed antennas on FR4 substrate (dielectric constant = 4.4) measures 9.2 mm by 4.1 mm and has a bandwidth of 3.5%. The peak gain of this antenna is 1.4 dBi. An overall size reduction of 70% is achieved compared to a conventional inverted-F antenna. Effects of dielectric loss tangent and material conductivity on the bandwidth and efficiency of these antennas are also investigated. Finally, two embedded antenna elements are analyzed to demonstrate the feasibility for a decoupled antenna pair consisting of switched and combining diversity schemes. Index Terms--Antenna, diversity, Hilbert, wireless.

Radiation at broadside from leaky waves is studied for one-dimensional periodic structures modeled by means of a transmission line periodically loaded by series or shunt loads. Radiation at broadside occurs via an axially fast spatial harmonic in a neighborhood of the open-stopband frequency; operation in such a frequency range is studied here by means of an approximate asymptotic Bloch analysis of the adopted equivalent network and a simple array-factor calculation of the radiated far field. The condition of equal values for the phase and attenuation constants of the radiating spatial harmonic is shown to give rise to maximum radiation at broadside in the lossless case and to the splitting of a single peak of the radiation pattern at broadside into two distinct peaks in both the lossless and the lossy cases. The 3 dB frequency band for broadside radiation is characterized in terms of the leaky-pole locations in the complex plane and an approximate formula for the antenna bandwidth is provided. Numerical results illustrating these properties are provided, including full-wave simulations of a specific structure through the method of moments. Index Terms--Broadside radiation, leaky-wave antennas, leaky waves, periodic structures.

In this work, an assessment of the influence of the field probes on the uncertainty in the measurements of the electric and magnetic field in the vicinity of aperture antennas is presented. A uniform aperture distribution is considered because the field of a tapered distribution aperture can be reduced to that of a uniform one. Moreover, the effect of probe size and configuration is presented through a comparison between the theoretically calculated and the expected values. Field probes of a single or more perpendicular dipoles are investigated. The maximum permissible length of the dipoles for an accurate field assessment depends on the field's gradient. In the regions where the relative amplitude and phase of the electric field along the measuring device does not exhibit considerable variation, even half-wavelength dipoles can be used. It is also found that probes with sizes less than 0.1[lambda] ensure measurement uncertainty less than 0.5 dB for field variation up to 7 dB/[lambda]. Index Terms--Antenna measurements, aperture antenna, near field.

Several electrically small resonant antennas employing the composite right/left-handed transmission line (CRLH-TL) are presented for integration with portable RF modules. The proposed antenna designs are based on the unique property of anti-parallel phase and group velocity of the CRLH-TL at its fundamental mode. In this mode, the propagation constant increases as the frequency decreases, therefore, a small guided wavelength can be obtained at a lower frequency to provide the small [[lambda].sub.g]/2 resonant length used to realize a compact antenna design. Furthermore, the physical size and the operational frequency of the antenna depend on the unit cell size and the equivalent transmission line model parameters of the CRLH-TL, including series inductance, series capacitance, shunt inductance and shunt capacitance. Optimization of these parameters as well as miniaturization techniques of the physical size of unit cell is investigated. A four unit-cell resonant antenna is designed and tested at 1.06 GHz. The length, width and height of the proposed antenna are 1/19 [[lambda].sub.0], 1/23 [[lambda].sub.0] and 1/83 [[lambda].sub.0], respectively. In addition, a compact antenna using a 2-D three by three mushroom like unit cell arrangement is developed at 1.17 GHz, showing that an increased gain of 0.6 dB and higher radiation efficiency can be achieved over the first prototype antenna. The same design is applied in the development of a circularly polarized antenna operating at 2.46 GHz. A 116[degrees] beamwidth with axial ratio better than 3 dB is observed. The physical size of the proposed mushroom type small antenna and the circularly polarized antenna is 1/14 [[lambda].sub.0] by 1/14 [[lambda].sub.0] by 1/39 [[lambda].sub.0] and 1/10 [[lambda].sub.0] by 1/10 [[lambda].sub.0] by 1/36 [[lambda].sub.0], respectively. Index Terms--Circular polarized antenna, composite right/left-handed transmission line (CRLH-TL), metamaterials, small antenna.

The perfectly matched layer (PML) in its most current form has shortcomings in certain cases involving propagation in anisotropic media, such as the whistler mode in a magnetized plasma, for which the vector component normal to the PML of the group velocity vector and the k-vector are anti-parallel with each other. We present a new type of PML that utilizes information on the k-vector direction by applying relevant spatial derivatives to the PML update equations. Derived expressions for the numerical reflection coefficient are used to quantify the performance of the PML for any incident angle. Numerical reflection calculations as well as time domain calculations are performed for whistler mode propagation in a magnetized plasma. We demonstrate the stability of the new PML and find that for the reflection coefficient r, values of up to -40 dB can be realized. Index Terms--Anisotropic, k-vector, perfectly matched layer (PML).

We present a unified approach of the description of the spatial and temporal distribution of radio signals within built-up radio communication links. This approach is based on a multiparametric stochastic model, which takes into account the characteristic features of built-up terrain and peculiarities of radio wave propagation related with multiple reflections, diffraction and scattering phenomena caused by obstructions surrounding both terminal antennas, the receiver and the transmitter. To describe fast fading phenomena, we propose a new general distribution of signal strength fast fading, which successfully covers the Ricean distribution in line-of-sight (LOS) and quasi-LOS conditions and the Rayleigh distribution in no line-of-sight multipath conditions usually used for description of land communication links. This new distribution leads to a multiparametric stochastic model. Based on this model, we present a strict estimation of scales of slow and fast fading and present the corresponding correlation functions in space and time domains, which describe slow and fast signal fluctuations. Finally, the power distribution in the angle-of-arrival (azimuth) domain, following the proposed stochastic approach, is considered and analyzed, both for uplink and downlink mobile communication channels. Index Terms--Fading phenomena, land communication links, scales of slow and fast fading, signal intensity distribution and angle of arrival in time and space domains, uplink and down link wireless communication.

A novel high-gain active composite right/left-handed (CRLH) metamaterial leaky-wave antenna (LWA) is presented. This antenna, which is designed to operate at broadside, is constituted by passive CRLH leaky-wave sections interconnected by amplifiers, which regenerate the power progressively leaked out of the structure in the radiation process in order to increase the effective aperture of the antenna and thereby its gain. The gain is further enhanced by a matching regeneration effect induced by the quasi-unilateral nature of the amplifiers. Both the cases of quasi-uniform and binomial field distributions, corresponding to maximum directivity and minimum side-lobe level, respectively, have been described. An active LWA prototype is demonstrated in transmission mode with a gain enhancement of 8.9 dB compared to its passive counterpart. The proposed antenna can attain an arbitrarily high gain by simple increase of the length of the structure, without penalty in terms of return loss and without requiring a complicated feeding network like conventional array antennas. Index Terms--Active antennas, composite fight/left-handed (CRLH) metamaterials, leaky-wave antennas (LWAs).

We investigate the decomposition of the time-reversal operator (DORT under its French language acronym) method applied to ultrawideband electromagnetic pulses propagating in dispersive and (continuous) inhomogeneons random media where volumetric scattering effects are important. We analyze the effects of random medium statistics on the time-reversal operator (TRO) eigenvalues and eigenvectors, and on subsequent selective focusing performance. We develop and employ a full time-domain DORT by tracking the excitation eigenvectors from a singular value decomposition of the TRO over the entire bandwidth of operation. We also study effects of frequency dispersion and conduction losses on the TRO and consider dispersion/loss compensation techniques to improve DORT operation in those cases. Index Terms--Decomposition of the time-reversal operator (DORT) method, electromagnetic (EM) propagation in random media, selective focusing, time-reversal (TR).

The effects of cavities located near the base of a ground plane-mounted coax-driven monopole antenna are investigated. The cavities are either embedded in the tubular antenna itself or in the region below the conducting surface. Coupled integral equations are formulated and solved to determine the distribution of current on the structure. Two primary functions of the cavities are discussed. 1) At certain frequencies the input impedance of the cavity is infinite and the current at the base of the antenna is forced to zero. A single structure may contain several cavities, each cavity having unique resonant frequencies. It is demonstrated that superposition of these cavities may provide multiple resonant frequencies within a large frequency band. The utility of base cavities in the design of an antenna that is decoupled from the ground plane on which it is mounted is discussed. 2) Regardless of frequency, the cavities affect the distribution of current on the structure and, concomitantly, the standing wave ratio and gain of the antenna. The cavities are shown to be efficient and physically-rigid tools for current-shaping and tuning coax-fed antennas. Results computed from solutions of the coupled integral equations are compared with those from physical measurements. Index Terms--Antenna feeds, integral equations, method of moments (MoM), monopole.

A novel technique for enhancing the impedance bandwidth of wireless terminal antennas is presented. By introducing resonant short circuit transmission lines to the long sides of the chassis edges, an effective electrical shortening of the terminal ground plane is achieved. This effect has been used to realize terminal ground planes with resonant lengths at high frequencies, such as GSM 1800/1900 MHz or UMTS 2 GHz, thereby extending the impedance bandwidth. The proposed technique has been validated by simulations and measurements. Three typical applications are presented where the introduction of wavetraps improves the bandwidth and/or in-band performance. Index Terms--Bandwidth, broadband communication, microstrip antennas, mobile antennas.

A source reconstruction technique from the measured near fields is proposed to obtain a set of equivalent currents that will characterize the forward and backward radiation patterns of an antenna. Once the equivalent sources are determined, the electromagnetic field at any aspect angle and distance from the antenna can be calculated. In this paper, the method is applied to the evaluation of the radiation from commercial antennas at any observation point. The electric field patterns of a DCS base station antenna at 1800 MHz and a horn antenna at 2500 MHz have been calculated and plotted at several distances from the antenna. This method can be used in characterizing the 'reference volumes' or exclusion zones for transmitting antennas dealing with the maximum levels of electromagnetic radiation safe for human exposure, as stated in many national and international regulations. Index Terms--Antenna measurement, equivalent magnetic currents, human exposure, near-field pattern, near-field to far-field transformation, non-ionizing EM fields.

Pulse-preserving capabilities of ultrawideband (UWB) antennas, which are measured in terms of two parameters--the fidelity factor and the pulse width stretch ratio, are analyzed with respect to variations of the antenna gain and the group delay of the radiated field. With the degrees of the gain and the group delay variations quantified by their respective standard deviations from constant values, Monte-Carlo simulations are performed to evaluate the effect of different gain and group delay functions using randomly generated Gaussian profiles. The means and the standard variations of the two performance parameter distributions are monitored and their two-dimensional profiles are specifically obtained for UWB antennas operating in 3.1-10.6 GHz. The analysis also demonstrates the use of the fidelity factor and the pulse width stretch ratio as useful characterizing parameters for UWB antennas. Index Terms--Antenna gain, fidelity, group delay, ultrawideband (UWB) antennas.

We propose a novel package topology integrating multilayer miniaturized antennas. Such a functional package is suitable for the design of a system-on-chip device, or of system-on-package applications. A stacked patch antenna is designed and integrated in a package using a low temperature co-fired ceramic process. The overall size of the package is 10.3 x 10.3 x 1.3 [mm.sup.3], and this package contains an 8.3 x 8.3 x 0.7 [mm.sup.3] internal space for the integration of chip-scale packaged components. The package is mounted on a 20 x 20 [mm.sup.2] ground plane to miniaturize the volume of the system. The antenna is designed to have two neighboring resonant frequencies at 5.264 and 5.355 GHz, resulting in a 140 MHz impedance bandwidth. However, the measured resonant frequencies occur at slightly higher frequencies due to manufacturing tolerances. Radiation patterns are similar to a conventional patch antenna. In addition, various parasitic effects rooted in the package size, ground size, antenna height, SMA connector, via misalignment, and the number of via holes and their locations are fully investigated. Index Terms--Functional package, package-level integrated antenna, system-on-chip, system-on-package (SOP).

A novel optimization procedure for the design of antennas for ultrawideband (UWB) wireless communication systems is presented. The optimization is based on the time-domain characteristics of the antenna. The optimization procedure was applied to a simplified version of the volcano smoke antenna proposed by Kraus. However, any other type of UWB antenna can be treated with the same technique. Our optimization procedure aims at finding an antenna not only with low VSWR but also a low-dispersion one which will ensure high correlation between the time-domain transmitting antenna input signal and the receiving antenna output signal. In pulse communications systems, usually an input signal form suited to a particular purpose is used. Hence, we strive to design the best antenna for a given input signal form. The optimization technique adopted here makes use of genetic algorithm (GA) search concepts. The electromagnetic analysis of the antenna is done by means of a finite-difference time-domain method using the commercially available CST Microwave Studio software. Index Terms--Correlation (fidelity), dispersion, genetic algorithms (GAs), indoor communication, monopole antenna, time-domain analysis, ultrawideband (UWB) antennas, ultrawideband communication.

Dielectric resonator antennas (DRAs) designed for broadband applications and excited by L-shaped probe are presented. The L-probe is housed under an air-filled groove between the DRA and the ground plane. A 32% matching bandwidth ([S.sub.11] < -10 dB) is achieved with broadside radiation patterns. The new structure is constructed from the same dielectric materials. Thus, it is mechanically better than other wideband DRAs that consist of more than one dielectric material such as the stacked DRA. Some results are verified experimentally. The performance of this DRA and those fed by traditional probes and slots are investigated numerically. In addition, comparisons between L-probe excited DRAs and L-probe excited microstrip patch antennas are discussed. Index Terms--Broadband antennas, dielectric resonator antennas (DRAs), microstrip antennas.

In this paper, we propose a novel modified T-shaped planar monopole antenna in that two asymmetric horizontal strips are used as additional resonators to produce the lower and upper resonant modes. As a result, a dual-band antenna for covering 2.4-and 5-GHz wireless local area network (WLAN) bands is implemented. In order to expand the lower band, a multiband antenna for covering the digital communications systems, personal communications systems, Universal Mobile Telecommunications Systems, and 2.4/5-GHz WLAN bands is also developed. Prototypes of the multiband antenna have been successfully implemented. Good omnidirectional radiation in the desired frequency bands has been achieved. The proposed multiband antenna with relatively low profile is very suitable for multiband mobile communication systems. Index Terms--Monopole antenna, multiband antenna, wireless communication.