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Designs of coplanar waveguide (CPW)-fed equilateral triangular-ring slot antennas with tuning-stub and triangular-ring slot coupled patch antennas are proposed and experimentally investigated. The impedance matching of the resonant frequency can be obtained only by adjusting the tuning-stub length for the proposed triangular-ring slot antenna with tuning-stub. For the design of ring-slot coupled patch antenna, slightly changing the patch size causes the tunable frequency-ratio f2/f1 between the first two operating frequencies to fall in the range of about 1.1-1.42. Details of the proposed designs are investigated by experimental as well as theoretical studies. [ABSTRACT FROM AUTHOR]

A rectangular dielectric resonator antenna (DRA) was studied theoretically and experimentally. The rectangular DRA is excited by a strip, which is compatible with a coaxial probe. Both linearly polarized (LP) and circularly polarized (CP) fields of the antenna are considered. In previous studies of the LP rectangular DRA, only the fundamental TE111 mode has received much attention. In this paper, it is found that the fundamental TE111 mode, together with the higher-order TE113 mode, can be used to design a wide-band LP DRA. The bandwidth of the dual-mode DRA can be over 40% for a conventional rectangular DRA with a simple feed. For the CP mode, a parasitic patch is attached on a side wall of the DRA to excite a degenerate mode. In both the LP and CP cases, the finite-difference time-domain (FDTD) method is used to analyze the problems. The results agree reasonably with measurements. [ABSTRACT FROM AUTHOR]

In this paper, we present indoor measurement results on the cluster angular spread (AS), the tap AS and its variation with different channel bandwidths. A frequency domain space alternating generalized expectation maximization (FD-SAGE) algorithm is employed to estimate the multipath components from the measured data. We then manually identify the clusters of the multipaths and calculate the tap and cluster AS is for each identified cluster. It is found that for the 100 MHz channels, the average tap AS is just few degrees less than the cluster AS and the difference diminishes for less channel bandwidth. [ABSTRACT FROM AUTHOR]

A patch antenna supported by a dielectric resonator is studied. This small antenna possesses the advantages offered by the folded patch antenna and the dielectric resonator antenna. Unlike most traditional small antennas, the proposed design has a relatively low cross-polarization, less than -20 dB. By using a dielectric material with ϵr = 10, the length of the antenna is about 15 percent of a free-space wavelength. The antenna is resonant at the center frequency of 1.265 GHz with an impedance band- width of ∼ 2.2% (10-dB bandwidth). It offers a maximum gain of 3 dBi and the measured radiation patterns are stable across the operating firquency range. Both simulation and measurement results are presented and compared. [ABSTRACT FROM AUTHOR]

In this paper, a printed wide-slot antenna fed by a microstrip line with a rotated slot for bandwidth enhancement is proposed and experimentally studied. Impedance, radiation, and gain characteristics of this antenna are presented and discussed. From experimental results, the measured impedance bandwidth, defined by 10 dB return loss, can reach an operating bandwidth of 2.2 GHz at operating frequencies around 4.5 GRz, which is about four times that of a conventional microstrip-line-fed printed wide-slot antenna. Also, the antenna gain within the operating band is measured and studied, and a 2-dB gain bandwidth of at least 1 GHz is achieved. [ABSTRACT FROM AUTHOR]

This paper shows the performance of a reflect array using the QUAD-EMC patch as the radiating element. The phase adjustment is made at a sub-array level by tuning the length of each driven patch. Therefore, this new design uses fewer of the required phase shifter elements. The phase diagram provides the shared phase to each QUAD-EMC unit. The return loss plot of a radiating unit excited by the microstrip line is studied. The connection between the phase diagram and the return loss plot is also discussed. Experiments have shown that we can get comparable results with those obtained by controlling the phase on each individual element. Bandwidth of 23% with 1.5 dB gain variation can be achieved when built on an FR4 substrate. The cross polarization level may be improved since there is enough room to place the straight delay lines. [ABSTRACT FROM AUTHOR]

A new design of a circularly polarized square-ring slot antenna is proposed. The circular polarization is achieved by a series microstrip-line-feed configuration coupling to two orthogonal sides of the square-ring slot. A parametric study is conducted using a commercial simulation software based on the method of moments, and the design procedure is established. The required ground-plane size of the proposed design for a given frequency is also indicated. Three antenna prototypes respectively operated at distinct frequency bands are constructed and measured for providing the simulation validation. Experimental results show that the proposed antenna has good circularly polarized radiations and the 3 dB axial-ratio bandwidth is more than 6%. [ABSTRACT FROM AUTHOR]

A diffraction field-focusing equation based on a specific conical-segment linearization procedure is derived for the Fresnel zone plate (FZP) lens of arbitrary curved profile and is applied for contrasting plane, spherical, parabolic and conical zone plate lenses, convex-side illuminated by a paraxial plane wave front. Two sets of 100-GHz curvilinear and plane FZP lenses are studied numerically with regards to their dimensions, axial focusing intensity and footprint, and frequency bandwidth. For the first set, where the curvilinear and plane lenses share a common lens base aperture and have equal focal lengths, the following new finding has resulted: regardless of their different in shape profiles the FZP lenses have equal zone numbers and produce similar axial focusing. The second set also consists of plane, spherical, parabolic and conical Lenses. They share a common apex, and have equal in diameter base apertures and focal lengths but different thicknesses. For such disposition and proportions, the FZP lenses possess different zone numbers and focusing parameters (gain, efficiency, footprint and bandwidth). The belief that the curvilinear FZP have superior (or inferior) electromagnetic characteristics, compared to those of the plane FZP lens with equal number of zones is not in general true. Their relative focusing qualities can vary significantly depending on the lens positioning and dimensions. [ABSTRACT FROM AUTHOR]

Exact expressions for the radiation quality factor Q and the gain pattern function of the corresponding antenna are derived and their properties are analyzed for crossed electric and magnetic dipole moment configuration. Both omni-directional and directional antennas with linear, elliptical, or circular polarization can achieve the same minimum radiation Q. The maximum gain of the antenna ranges from 3/2 to 3. The maximum gain of three can be achieved only for linear polarization when the source vectors make aright angle and the amplitudes of the TM and the It modes are equal. The increase in the maximum gain from 3/2 for omni-directional antennas to 3 for directional antennas does not re quire any increase in the radiation Q, which suggests that practical directional antennas with higher gain may be realized with smaller size compared with small omni-directional antennas assuming similar operation bandwidths. [ABSTRACT FROM AUTHOR]

To address the need for fundamental universally valid definitions of exact bandwidth and quality factor (Q) of tuned antennas, as well as the need for efficient accurate approximate formulas for computing this bandwidth and Q, exact and approximate expressions are found for the bandwidth and Q of a general single-feed (one-port) lossy or lossless linear antenna tuned to resonance or antiresonance. The approximate expression derived for the exact bandwidth of a tuned antenna differs from previous approximate expressions in that it is inversely proportional to the magnitude |Z'0 (&omega0) | of the frequency derivative of the input impedance and, for not too large a bandwidth, it is nearly equal to the exact bandwidth of the tuned antenna at every frequency &omega0, that is, throughout anti-resonant as well as resonant frequency bands. It is also shown that an appropriately defined exact Q of a tuned lossy or lossless antenna is approximately proportional to |Z'0 (&omega0) | and thus this Q is approximately inversely proportional to the bandwidth (for not too large a bandwidth) of a simply tuned antenna at all frequencies. The exact Q of a tuned antenna is defined in terms of average internal energies that emerge naturally from Maxwell's equations applied to the tuned antenna. These internal energies, which are similar but not identical to previously defined quality-factor energies, and the associated Q are proven to increase without bound as the size of an antenna is decreased. Numerical solutions to thin straight-wire and wire-loop lossy and lossless antennas, as well as to a Yagi antenna and a straight-wire antenna embedded in a lossy dispersive dielectric, confirm the accuracy of the approximate expressions and the inverse relationship between the defined bandwidth and the defined Q over frequency ranges that cover several resonant and antiresonant frequency bands. [ABSTRACT FROM AUTHOR]

In this paper, we discuss a kind of meander antenna which is designed for digital audio broadcasting (DAB) reception in BAND-III upper band (210-240 MHz). Three resonators in addition to a driven element were constructed on the topside of a printed circuit board. On the backside of it, several coupling stubs were introduced to tune resonant frequencies to the required pass- band. Resonators with different lengths are resonated at different frequencies and these multiple resonances are responsible for an enhancement in bandwidth. With the help of backside coupling, it is easy to tune multiple frequencies to the required pass-band. It is also found that current density of the associated elements is increased by backside coupling. According to experimental results, the designed antenna reaches a bandwidth around 13.3% (return loss >10 dB) in the range of 210-240 MHz. [ABSTRACT FROM AUTHOR]

The ability of a single layer strip fed printed monopole, which has a serial-slot and an end-stepped feed-strip, to operate at dual Industrial, Scientific, and Medical-band (2.4 and 5.8 GRz bands) is demonstrated. This antenna combines omni-di- rectional and broad bandwidth in an easy to fabricate structure. Experimental results indicate that the VSWR 2:1 bandwidths achieved were 8.2% and 18.2% at 2.45 GHz and 5.5 GHz. Effects of varying the serial-slot dimensions and the ground-plane size on the antenna performance are also described. [ABSTRACT FROM AUTHOR]

A square planar metal-plate monopole antenna fed by using a novel trident-shaped feeding strip is presented. With the use of the proposed feeding strip, the square planar monopole antenna studied shows a very wide impedance bandwidth of about 10 GHz (about 1.4-11.4 GHz, bandwidth ratio about 1:8.3), which is larger than three times the bandwidth obtained using a simple feeding strip (about 1.5-3.3 GHz, `bandwidth ratio about 1:2.3). In addition, the proposed feeding strip can be integrated with the square planar monopole, that is, the feeding strip and the square planar monopole together can be easily fabricated using a single metal plate, making the proposed antenna easy to construct at a low cost Details of the experimental and simulation results for the proposed planar monopole antenna are presented and analyzed. [ABSTRACT FROM AUTHOR]

A novel planar tapered-slot-fed annular slot antenna is proposed in this paper. The antenna utilizes a unique tapered-slot feeding structure and simultaneously possesses ultrawide band- width, almost uniform radiation patterns, and low profile. It is, hence, adequate for ultrawide-band (UWB) applications. By means of a normalized antenna transfer function; both frequency domain and time domain characteristics of the antenna are carefully investigated. Two measures, the uniformity related to the radiation patterns and the fidelity associated with the transient behaviors, are used to quantitatively describe the performance of an antenna over such an ultrawide bandwidth. Effects of varying the antenna's geometric parameters on the performance are then investigated. Finally, the influence of minimizing the antenna dimension is discussed at the end of the paper. [ABSTRACT FROM AUTHOR]

We report on the use of a genetic algorithm (GA) in the design optimization of electrically small wire antennas, taking into account of bandwidth, efficiency and antenna size. For the antenna configuration, we employ a multisegment wire structure. The Numerical Electromagnetics Code (NEC) is used to predict the performance of each wire structure. To efficiently map out this multiobjective problem, we implement a Pareto GA with the concept of divided range optimization. In our GA implementation, each wire shape is encoded into a binary chromosome. A two-point crossover scheme involving three chromosomes and a geometrical filter are implemented to achieve efficient optimization. An optimal set of designs, trading off bandwidth, efficiency, and antenna size, is generated. Several GA designs are built, measured and compared to the simulation. Physical interpretations of the GA-optimized structures are provided and the results are compared against the well-known fundamental limit for small antennas. Further improvements using other geometrical design freedoms are discussed. [ABSTRACT FROM AUTHOR]

Analysis of a dielectric resonator antenna (DRA) fed by a waveguide probe is presented. The probe is excited by the dominant mode of a waveguide and extends into the DRA through an aperture in the waveguide wall. The DRA has, in general, an arbitrary shape and resides on an infinite ground plane, which coincides with the exterior of the waveguide broad wall. A simple and efficient analysis procedure is implemented where the problem is divided into two parts. In the upper part, the input impedance of the DRA excited by a coaxial probe is obtained with respect to the feeding position on the ground plane independent of the waveguide part. Then the input impedance is transformed to the waveguide part as a concentrated load at the end of the probe connected to the waveguide wall. The effect of the wall thickness is taken into account by modeling the section of the probe passing through the waveguide wall as a coaxial cable transmission line supporting the transverse electromagnetic mode. Thus the DRA input impedance is transferred from the ground plane reference to the waveguide inner wall reference. Results obtained using the method of moments are compared with those obtained using the finite-difference time-domain method and exhibit very good agreement. The procedure is used to achieve a bandwidth of 50% for a stacked DRA excited by a waveguide probe. [ABSTRACT FROM AUTHOR]

The goal of this study is to improve the bandwidth of a miniaturized antenna. The proposed technique combines a slot antenna and a dielectric resonator antenna (DRA) to effectively double the available bandwidth without compromising miniaturization or efficiency. With proper design it is observed that the resonance of the slot and that of the dielectric structure itself may be merged to achieve extremely wide bandwidth over which the antenna polarization and radiation pattern are preserved. In addition, using the DRA, a volumetric source, improves the radiation power factor of the radiating slot. A miniaturized antenna figure of merit (MAFM) is defined to simultaneously quantify aspects of miniaturized antenna performance including the degree of miniaturization, efficiency, and bandwidth. Figures for various common types of antennas are given and compared with that of the proposed structures. In order to determine the effects of varying design parameters on bandwidth and matching, sensitivity analysis is carried out using the finite-difference time-domain method. Numerous designs for miniaturized slot-fed dielectric resonator antennas are simulated and bandwidths exceeding 25% are achieved. Two 2.4 GHz antennas are built, characterized, and the results compared with theory. [ABSTRACT FROM AUTHOR]

A monopolar patch antenna that utilizes a band- width broadening technique is investigated experimentally and numerically. The proposed antenna consists of a monopole that is formed by connecting four trapezoidal plates orthogonally. A circular patch, which is shorted to the circular ground plane by four shorting wires, is placed at the top of the monopole. The antenna possesses 10-and 14-dB return loss bandwidths of 138% and 107.2% respectively, which is about 49 times that of the corresponding monopolar wire-patch antenna. Also, it provides monopole-like radiation patterns over such wide operating bandwidth. As the proposed antenna can achieve such wide impedance bandwidth with relatively low profile, it is very suitable for multi-band mobile communication systems. [ABSTRACT FROM AUTHOR]

Reduced size microstrip monopole slot antennas with different slot shapes- straight, L and inverted T, and placed on a small ground plane, are investigated. The ground plane size is 50 mm × 80 mm, which is about the size of a typical PC Wireless card. Detailed simulation and experimental investigations are conducted to understand their behavior and optimize for broad- band operation. It is shown that, the variation in the slot shape, from straight to L and T shapes, helps in generating additional resonances, which when coupled to the original resonances of the slot, further increases impedance bandwidths. The bent shapes of the L and T slots reduce their height and provide more space on the ground plane for electronics. A mirror image dual L-slot antenna, placed at two adjacent corners of the ground plane, is also investigated and optimized for the polarization diversity. They pro- vide an impedance bandwidth of 87%, with near orthogonal radiation characteristics. The measured impedance bandwidths (S11 = -10 dB) of up to 60%, 84%, and 80% are achieved for these straight, L and inverted T slots respectively, by suitably selecting their design parameters. The simulation results are in good agreement with the experimental data considering several practical issues. [ABSTRACT FROM AUTHOR]

The influence of material coverings on the antenna quality factor is investigated for radiators formed by thin electric or magnetic line sources. It is shown that thin uniform and syms metric layers of arbitrary passive materials (including Veselago, left-handed, or double-negative materials) cannot help to overcome the bandwidth limitations imposed by the amount of energy stored in the antenna reactive field. Alternative possibilities offered by complex composite materials in the antenna design are identified. [ABSTRACT FROM AUTHOR]

Planar periodic metallic arrays behave as artificial magnetic conductor (AMC) surfaces when placed on a grounded dielectric substrate and they introduce a zero degrees reflection phase shift to incident waves. In this paper the AMC operation of single-layer arrays without vias is studied using a resonant cavity model and a new application to high-gain printed antennas is presented. A ray analysis is employed in order to give physical insight into the performance of AMCs and derive design guidelines. The bandwidth and center frequency of AMC surfaces are investigated using full-wave analysis and the qualitative predictions of the ray model are validated. Planar AMC surfaces are used for the first time as the ground plane in a high-gain microstrip patch antenna with a partially reflective surface as superstrate. A significant reduction of the antenna profile is achieved. A ray theory approach is employed in order to describe the functioning of the antenna and to predict the existence of quarter wavelength resonant cavities. [ABSTRACT FROM AUTHOR]

A promising way to reduce the problems created by surface waves in printed phased array antennas is to use an electromagnetic bandgap (EBG) substrate instead of a standard dielectric. Two metallo-dielectric EBG substrates well suited for phased array applications have been designed and tested. One of them has a compact unit cell and exhibits a broad bandwidth performance. The other ERG structure has a narrower bandwidth but is simple to manufacture and has a low mechanical profile. Single radiating elements and a small linear array have been manufactured on a standard dielectric substrate and on the ERG substrates. The measurements show a significant improvement in radiation efficiency as well as of the front to back ratio for the antennas manufactured on the ERG substrates compared to the ones obtained for the antennas manufactured on the standard dielectric substrate. These results clearly demonstrate the effectiveness of the EBG substrates in reducing the surface and guided waves. [ABSTRACT FROM AUTHOR]

A periodic ground plane may be built to either stop the propagation of wave or support a quasi transverse electromagnetic wave along the surface. The former is called a soft surface, and the latter is a hard surface. However, a soft or a hard surface can only be realized in certain frequency and wavenumber regions; therefore, it is important to identify the bandwidth for the surface so that it can be used efficiently. The bandwidth for soft and hard operations of a ground plane has been previously characterized by studying the reflection of normal and oblique plane waves with the real angle of incidence. In this paper, the band-width for soft and hard operations of a periodic ground plane is defined as a wavenumber-frequency region in which the complex value of reflection coefficient is inside a circle with the radius of 1/&radic2; and centered at -1 or 1 for soft or hard operation, respectively. This definition gives a unified approach to characterize the bandwidth in both the visible (k²x + k²y < k²0) and surface wave (k²x + k²y > k²0) regions. The paper uses a newly developed numerical technique referred to as the spectral finite-difference time-domain (FDTD) method, which is capable of calculating the reflection coefficient and impedance of the surface for any given set of wavenumber and frequency of the incident wave including the surface wave region. By using this method, the reflection coefficients and impedances of a corrugated dielectric-lined surface and a mushroom-like EBG are calculated, and the bandwidth for soft, hard, and perfect magnetic conductor like behavior are specified. [ABSTRACT FROM AUTHOR]

Channel sounding techniques are used to investigate and compare two micro-cellular environments: regular and chaflane street corners, at four different frequencies using a network analyzer. Parameters are extracted from the power delay profile, which is obtained as the inverse Fourier of the measured frequency response. It is shown that, for line of sight (LoS), delay spread (US) decreases 10 ns in regular corners and 5 ns in chaflane when frequency varies from 450 to 2400 MHz. For non line of sight (NLoS), RMS DS is around 60 ns in both environments. Frequency correlation is higher in chaflanes than in regular street corners and correlation decreases when the distance in frequency increases. Tapped delay line models are obtained at each frequency in each environment for LoS and NLoS. Finally, for LoS, the coherence bandwidth is bigger in chaflanes than in regular street corners, and it is also observed that it grows as frequency increases. However, for NLoS, the bandwidth remains steady around 4 MHz. [ABSTRACT FROM AUTHOR]

This paper presents a novel design of low-cost broad-band dual-polarized microstrip arrays. The antenna uses the slot-coupled feed for one polarization, while the microstrip line feed with slotted ground plane is used for the other polarization it can make good use of the space on both sides of the ground plane, as the feed circuits for two orthogonal polarizations are placed on each side of the ground plane, respectively. The prototype four-element array designed at C band yields a bandwidth of more than 14% at both ports, and isolation below -30 dB. Good broadside radiation patterns are observed, and the cross-polar levels are below -20 dB at both E- and H-planes. [ABSTRACT FROM AUTHOR]

Thin, broad-band, E-shaped microstrip patch antennas (ESPAs), operating in the 5-6 GHz frequency range, are presented. They are intended for high-speed (IEEE 802.lla, 54 Mb/s) wireless computer local area networks (WLAN) and other wireless communication systems. They are suitable for WLAN adaptor cards in the PCMCIA (also known as PC) format, allowing users of current notebook computers to upgrade to this high-speed wireless standard at a low cost. Importantly, our antennas are thin enough to be accommodated in a PCMCIA card of standard 5-mm thickness, without making the antenna end thicker than the card itself. Two different closely spaced antenna pairs are also presented for diversity. A new ESPA configuration with a microstrip feed is presented for easy integration with microwave transceivers. In all cases, within the two WEE 802.lla WLAN bands (5.15-5.35 GHz and 5.725-5.825 GHz), the reflection coefficient at the antenna input is < -10 dB and in both antenna pairs, mutual coupling between the two antennas is < -20 dB. [ABSTRACT FROM AUTHOR]

In this paper we analyze the stability and the accuracy of finite-difference time-domain (FDTD) algorithms using Z-transform technique. Conventional tune-staggered approximation of the time-derivative is replaced by a rational transfer function discrete-time filter. Then a generalized formulation of the FDTD time-stepping is presented. Finally, we show that it is possible significantly reduce the time-sampling error of FDTD algorithm by properly choosing the transfer function coefficients. [ABSTRACT FROM AUTHOR]

In this contribution, the problem of accurately representing thin wires within the finite-difference time-domain (FDTD) mesh is addressed by means of a method based on the weighted residual (WR) interpretation of the FDTD algorithm. Results for wire dipoles and wire transmission lines, obtained using the proposed method, are presented and compared to those obtained using existing techniques. It is shown that the proposed method yields results which are more accurate and are less dependent on the choice of cell size than other approaches and, hi addition, lends itself well to being extended for more complicated structures. Details of the calculation of the update equations are given. [ABSTRACT FROM AUTHOR]

Evolutionary algorithms are powerful optimization and design tools, and the design of fitness function is their crucial phase. The ruggedness of a fitness function landscape has a profound effect on optimization speed. The choice of objectives and penalty coefficients are important problems for evolutionary antenna design, because these parameters influence the ruggedness of the fitness function landscape. In this paper, we analyze several fitness function landscapes for evolutionary design of dipole antennas using the method of basin evaluation. Our approach makes it possible to compare different fitness functions and thus define proper fitness functions for evolutionary antenna design. [ABSTRACT FROM AUTHOR]

This paper proposes an optimization-design method for the frequency selective surface (FSS) based on the genetic algorithm (GA) incorporated with a geometry-refinement technique. The present method takes the connectivity condition of the elements into consideration, thereby resulting in an easy fabrication. As an example, we design the multiband single-layer FSS for transmitting L hand (1.5 GHz band) and S band (2.5 GHz band) and also reflecting Ka band (20/30 GHz band). The designed FSS has bandwidths broader than previous FSSs. Finally, the validity of the present method is proved by the agreement between the calculated and the measured transmission responses for the designed FSS. [ABSTRACT FROM AUTHOR]

An oppositely shorted dual-band stacked patch planar inverted-F antenna (PIFA) is developed. RF switches are integrated to the shorting straps of the stacked patches to make a tunable PIFA. The L band switch yields 0.45-dB insertion loss and 10-dB isolation bandwidth (BW) of 108% at 1.8 GHz. The tunable PIFA yields 10% frequency tunability BW at 745 MHz when the number of upper radiating patch's shorting straps changes and 20% BW at 1137 MHz when the number of tower radiating patch's shorting straps changes. Independent lower and upper frequency tunings are achieved through this technique. [ABSTRACT FROM AUTHOR]

This paper reports a dual frequency dual layer circularly polarized reftectarray operating in the C and Ka bands. A 0.5-m right-hand circularly polarized planar reflectarray antenna is designed using microstrip ring elements of variable rotations to achieve a cophasal beam at broadside. The microstrip ring elements are more compact than the traditional reflectarray elements and can minimize blockage for the multilayer multifrequency applicatious. The highest efficiencies measured are 46% at 7.3 GHz and 38% at 31.75 6Hz. The tested cross-polarization levels are -21 dB at 7.3 GHz and -29.2 dB at 31.75 GHz at the broadside direction. The tested results show that the designed ring element is suitable for both the single and dual layer applications with good bandwidth and circularly polarized performance. [ABSTRACT FROM AUTHOR]

The growing demand for broad-band wireless communication links and the lack of wide frequency bands within the conventional spectrum, causes us to seek bandwidth in the higher microwave and millimeter-wave spectrum at extremely high frequencies (EHF) above 30 GHz. One of the principal challenges in realizing modern wireless communication links in the EHF band are phenomena occuring during electromagnetic wave propagation through the atmosphere. A space-frequency approach for analyzing wireless communication channels operating in the EIIF band is presented. Propagation of the electromagnetic radiation is studied in the frequency domain, enabling consideration of ultrawide-band modulated signals. The theory is employed for the analysis of a communication channel operating at EHF which utilizes pulse amplitude modulated signals. The atmospheric absorptive and dispersive effects on pulse propagation delay, pulse width and distortion are discussed. The theory and model are demonstrated in a study of ultrashort-pulse transmission at 60 GHz. [ABSTRACT FROM AUTHOR]

Ray tracing models are known to yield accurate results if a sufficient number of terms (e.g. diffraction mechanisms) are accounted for in the asymptotic formulation. For wireless applications one desires a ray analysis in which the fewest number of terms are retained, to obtain accurate and computationally efficient results. When retaining a subset of scattering mechanisms in a ray solution, validation is desirable via a rigorous numerical model. In the work presented here the multilevel fast-multipole algorithm is used to validate ray-tracing models for complex environments, including forest-like media. [ABSTRACT FROM AUTHOR]

A novel forward backward iterative scheme for solving the three-dimensinoal (3-D) electric field integral equation is presented. This communication details bow a naive extension of a 2-0 forward backward algorithm to 3-0 problems results in convergence difficulties due to spurious edge effects. The method proposed in this communication postulates the use of local "buffer regions" to suppress these unwanted effects and ensure stability. Results are presented illustrating the convergence of the algorithm when applied to scattering by a 15&lamda; square metallic plate with an aperture and a metallic right-angled wedge. [ABSTRACT FROM AUTHOR]

This communication presents a novel linearly polarized pattern recon-figurable microstrip parasitic array. Specifically, this antenna uses four switches (currently copper strips for proof of concept) to recon-figure the radiation pattern into three variations over a shared 2:1 VSWR bandwidth, and has potential applications in mobile communication devices and large phased antenna arrays. Both measured and simulated results of a microstrip parasitic array are provided. The effects of changes in physical dimensions and directions for future work are also discussed. [ABSTRACT FROM AUTHOR]

We consider a stochastic-ray model of wave propagation based on the theory of random walks that accounts for only two parameters: the amount of clutter and the amount of absorption in the environment. This model applies to indoor and out- door environments, characterized by a large number of (small) scattering objects. Examples are microcells for personal communication and networks of multihop wireless sensors or laptop computers. We extend our previous results on narrow-band signals to impulse waveforms, deriving a closed form solution for the power delay profile of the received signal. [ABSTRACT FROM AUTHOR]

The traditional Sierpinski gasket monopole antenna is well known for its multiband behavior, but it cannot be printed on the circuit board of a portable wireless device due to the limited space availability. In this paper a modified Sierpinski gasket monopole antenna is presented that possesses a small physical size, high efficiency and the ability to allocate both the 2.4 and 5.2 GHz Industrial Scientific and Medical bands without the need of a matching network. The modified element respects the multiband behavior of the gasket since the input impedance characteristics of the upper bands maintain their symmetry. Several modification techniques are proposed making the monopole very flexible in terms of band allocation and fine-tuning. The dimensions of the ground plane are also proven to play a significant role on the operational bandwidth of the antenna system. [ABSTRACT FROM AUTHOR]

This paper describes novel configurations of shorted fractal Sierpinski gasket antenna. The antenna uses half the structure of a conventional Sierpinski gasket antenna and is folded over to be parallel to the ground plane, to form an element similar to that of the inverted L antenna. A quasi log periodic resonance behavior is obtained with a shorting pin placed at the far end of the antenna. Several configurations are shown and a design using two shorting pins which improves the bandwidth at the fundamental band is also demonstrated. [ABSTRACT FROM AUTHOR]

The recent advances in such highly integrated RF transceivers as radio system-on-chip and radio system-in-package have called for the parallel development of compact and efficient antennas. This paper addresses the development of a new type of dielectric chip antenna known as integrated circuit package antenna (ICPA) for highly integrated RF transceivers. A compact ICPA of this type has, for the first time, been designed and fabricated in a ceramic ball grid array (CBGA) package format. The novel ICPA, except economical advantage of mass production and automatic assembly, has potential benefit to the system-level board miniaturization and the system-level manufacturing facilitation. The simulated and measured antenna performance of the ICPA is presented. The effects of the different physical parts of the ICPA on the antenna performance are investigated. Results show that the ICPA achieved impedance bandwidth of 4.1% and radiation efficiency of 72 %, and gain of 4.8 dBi at 5.7 15 GHz. [ABSTRACT FROM AUTHOR]

The design and measured results of a rectangular U-slot patch antenna proximity fed by a double-II stub feed are described. Using approximately 0.09λ of air gap separating the upper and lower dielectric, an impedance bandwidth of 26% centered at 4.4 GHz and a gain of 6 dBi have been achieved. The proposed antenna is noted to be tolerable to lateral displacement of the feed and produces a better impedance matching than the single II-stub antenna [6]. The radiation patterns obtained are stable across the passband. [ABSTRACT FROM AUTHOR]

A novel leaky-wave antenna based on an image nonradiative dielectric guide with two dielectric slabs is designed, fabricated and measured. By selecting appropriate values of permittivities and thicknesses for the two slabs, the gain bandwidth can be enhanced to four times wider than the ordinary single-layer nonradiative dielectric antenna. With appropriate thickness of the dielectric slab, the beamwidth can also be adjusted. [ABSTRACT FROM AUTHOR]

Local multipoint distribution systems (LMDS), which are operating worldwide in the frequency range of 26 to 43 GHz, have large bandwidths of 01 up to 2 GHz, but a very limited area coverage due to line of sight constraints and large propagation losses. As suggested in the Cellular Radio Access for Broadband Services (CRABS) Report [1], a high spectral efficiency can be obtained for a regular network of squared cells with a dual frequency and polarization reuse scheme. However, this frequency and polarization reuse leads to cochannel and adjacent channel interference. In this paper, we report a systematic two-dimensional study of interference in such a regular LMDS network for the downlink and uplink in order to assess the impact of different geometric and propagation parameters. The paper reports simple formulas to estimate the areas of high interference levels within an LMDS cell as a function of the half-power beamwidth of the customer-site antennas for the downlink. The effect on the carrier-to-interference distribution over a LMDS cell is evaluated by varying the half-power beamwidth of the customer-site antennas, the time percentage of short term enhancement due to atmospheric multipath and focusing effects and the cell dimensions. We also introduce a simple technique by reorientation of the customer-site antennas for interference reduction. The results presented in this paper can be used to carry out system-level design for interference-limited LMDS cells. [ABSTRACT FROM AUTHOR]

In this paper, we describe an electromagnetic genetic algorithm (GA) optimization (EGO) application developed for the cluster supercomputing platform. A representative patch antenna design example for commercial wireless applications is detailed, which illustrates the versatility and applicability of the method. We show that EGO allows us to combine the accuracy of full-wave EM analysis with the robustness of GA optimization and the speed of a parallel computing algorithm. A representative patch antenna design case study is presented. We illustrate the use of EGO to design a dual-band antenna element for wireless communication (1.9 and 2.4 GHz) applications. The resulting antenna exhibits acceptable dual-band operation (i.e., better than -10 dB return loss with 5.3 and 7% operating bandwidths at 1.9 and 2.4 GHz) while maintaining a cross-pol maximum field level at least 11 dB below the co-pol maximum. [ABSTRACT FROM AUTHOR]

The concept of a novel reactive impedance surface (RIS) as a substrate for planar antennas, that can miniaturize the size and significantly enhance both the bandwidth and the radiation characteristics of an antenna is introduced. Using the exact image formulation for the fields of elementary sources above impedance surfaces, it is shown that a purely reactive impedance plane with a specific surface reactance can minimize the interaction between the elementary source and its image in the RIS substrate. An RIS can be tuned anywhere between perfectly electric and magnetic conductor (PEC and PMC) surfaces offering a property to achieve the optimal bandwidth and miniaturization factor. It is demonstrated that RIS can provide performance superior to PMC when used as substrate for antennas. The RIS substrate is designed utilizing two-dimensional periodic printed metallic patches on a metal-backed high dielectric material. A simplified circuit model describing the physical phenomenon of the periodic surface is developed for simple analysis and design of the RIS substrate. Also a finite-difference time-domain (FDTD) full-wave analysis in conjunction with periodic boundary conditions and perfectly matched layer walls is applied to provide comprehensive study and analysis of complex antennas on such substrates. Examples of different planar antennas including dipole and patch antennas on RIS are considered, and their characteristics are compared with those obtained from the same antennas over PEC and PMC. The simulations compare very well with measured results obtained from a prototype λ/10 miniaturized patch antenna fabricated on an RIS substrate. This antenna shows measured relative bandwidth, gain, and radiation efficiency of BW = 6.7%, G = 4.5 dBi, and er = 90%, respectively, which constitutes the highest bandwidth, gain, and efficiency for such a small size thin planar antenna. [ABSTRACT FROM AUTHOR]

A wide-band, dual polarized printed antenna is designed and developed in this paper. The antenna is based upon an aperture stacked patch layout and incorporates a simple dual-layered feeding technique to achieve dual-polarized radiation. The printed antenna has a measured to dB return loss bandwidth of 52% and an isolation between the excitation ports of greater than 39 dB over this frequency range. The gain of the antenna is 7.4 dBi ± 0.4 dB and the typical issues associated with incorporating an aperture excited solution are resolved by using a cross-shaped reflector patch to ensure the front-to-back ratio is greater than 20 dB. [ABSTRACT FROM AUTHOR]

Wireless communication using multiple-input multiple-output (MIMO) systems enables increased spectral efficiency and link reliability for a given total transmit power. Increased capacity is achieved by introducing additional spatial channels which are exploited using space-time coding. The spatial diversity improves the link reliability by reducing the adverse effects of link fading and shadowing. The choice of coding and the resulting performance improvement are dependent upon the channel phenomenology. In this paper, experimental channel-probing estimates are reported for outdoor environments near the personal communication services frequency allocation (1790 MHz). A simple channel parameterization is introduced. Channel distance metrics are introduced. Because the bandwidth of the channel-probing signal (1.3 MHz) is sufficient to resolve some delays in outdoor environments, frequency-selective fading is also investigated. Channel complexity and channel stationarity are investigated. Complexity is associated with channel-matrix singular value distributions. Stationarity is associated with the stability of channel singular value and singular vector structure over time. [ABSTRACT FROM AUTHOR]

The dissipated power and the directivity of antennas in a homogeneous, lossy medium are systematically analyzed in this paper. The antennas are ideal and located inside a lossless sphere. In the lossy space outside the sphere, the electromagnetic fields are expanded in a complete set of vector wave functions. The radiation efficiency, the directivity, and the power gain are defined for antennas in a lossy medium, and the optimal values of these quantities are derived. Simple relations between the maximal number of ports, or channels, an antenna can use and the optimal directivity and gain of the antenna are presented. [ABSTRACT FROM AUTHOR]

In this paper, the unique features of periodic magneto-dielectric meta-materials in electromagnetics are addressed. These materials, which are arranged in periodic configurations, are applied for the design of novel EM structures with applications in the VHF-UHF bands. The utility of theses materials are demonstrated by considering two challenging problems, namely, design of miniaturized electromagnetic band-gap (EBG) structures and antennas in the VHF-UHF bands. A woodpile EBG made up of magneto-dielectric material is proposed. It is shown that the magneto-dielectric woodpile not only exhibits band-gap rejection values much higher than the ordinary dielectric woodpile, but also for the same physical dimensions it shows a rejection band at a much lower frequency. The higher rejection is a result of higher effective impedance contrasts between consecutive layers of the magneto-dielectric woodpile structure. Composite magneto-dielectrics are also shown to provide certain advantages when used as substrates for planar antennas. These substrates are used to miniaturize antennas while maintaining a relatively high bandwidth and efficiency. An artificial anisotropic meta-substrate having μr > ∊r, made up of layered magneto-dielectric and dielectric materials is designed to maximize the bandwidth of a miniaturized patch antenna. Analytical and numerical approaches, based on the anisotropic effective medium theory (AEMT) and the finite-difference time-domain (FDTD) technique, are applied to carry out the analyzes and fully characterize the performance of finite and infinite periodic magneto-dielectric meta-materials integrated into the EBG and antenna designs. [ABSTRACT FROM AUTHOR]

An infinitesimally thin spiral antenna, sandwiched by bottom and top dielectric layers having the same relative permittivity, is analyzed under the condition that the dielectric layers are of finite extent and the antenna is backed by an infinite conducting plane. As the thickness of the top dielectric layer increases, the input impedance and axial ratio (AR) vary in an oscillatory fashion, with a period slightly larger than one-half of the guided wavelength of a wave propagating in an unbounded dielectric material. These oscillatory variations are reduced by adding a layer, called the "anti-reflection layer (ARL)," to the top dielectric layer. A representative spiral antenna with an ARL shows a frequency bandwidth of approximately 11% for a 3-dR AR criterion, having a gain of approximately 13 dBi (6 dBi higher than a printed spiral antenna without the top dielectric and ARL) and a voltage standing wave ratio of less than 1.2. [ABSTRACT FROM AUTHOR]