Showing papers in "Progress in Electromagnetics Research B in 2011"
TL;DR: In this paper, a low proflle, compact, wide beam and wide band printed double layered exponentially tapered slot antenna (DTSA) with a coplanar waveguide (CPW) feed meant for wide scan active phased array antenna in X-band has been presented.
Abstract: Design and development of a low proflle, compact, wide beam and wide band printed double layered exponentially tapered slot antenna (DTSA) with a coplanar waveguide (CPW) feed meant for wide scan active phased array antenna in X-band has been presented. DTSA satisfles the requirements on the maximum re∞ection coe-cient of i • i10dB for §60 - and §45 - scan from broadside in H- and E- planes, respectively with a moderate gain of 4{7dBi. Realized antenna has shown a symmetric pattern together with moderately high gain, low cross-polarization and 3dB beam width better than §60 - and §45 - in H- and E- planes, respectively. The designed structure is expected to flnd applications in mounting platforms with limited RF real estate available to it like in military aircrafts, owing to its easy integration with the uni-planar monolithic millimeter-wave integrated circuits.
141 citations
TL;DR: In this article, the authors present a novel and highly improved formulation of scattering matrices that is consistent with convention, more efficient to implement, and more versatile than what has been otherwise presented in the literature.
Abstract: The literature describing scattering matrices for semi- analytical methods almost exclusively contains ine-cient formulations and formulations that deviate from long-standing convention in terms of how the scattering parameters are deflned. This paper presents a novel and highly improved formulation of scattering matrices that is consistent with convention, more e-cient to implement, and more versatile than what has been otherwise presented in the literature. Semi-analytical methods represent a device as a stack of layers that are uniform in the longitudinal direction. Scattering matrices are calculated for each layer and are combined into a single overall scattering matrix that describes propagation through the entire device. Free space gaps with zero thickness are inserted between the layers and the scattering matrices are made to relate flelds which exist outside of the layers, but directly on their boundaries. This framework produces symmetric scattering matrices so only two parameters need to be calculated and stored instead of four. It also enables the scattering matrices to be arbitrarily interchanged and reused to describe longitudinally periodic devices more e-ciently. Numerical results are presented that show speed and e-ciency can be increased by more than an order of magnitude using the improved formulation.
117 citations
TL;DR: Results using flre ∞y algorithm shows better performances than that of artiflcial bees colony optimization technique provided that the same number of function evaluations has been considered for both the algorithms.
Abstract: This paper describes the application of two recently developed metaheuristic algorithms known as flre ∞y algorithm (FFA) and artiflcial bees colony (ABC) optimization for the design of linear array of isotropic sources. We present two examples: one for broad side arrays and the other for steerable linear arrays. Three instances are presented under each category consisting of difierent numbers of array elements and array pattern directions. The main objective of the work is to compute the radiation pattern with minimum side lobe level (SLL) for specifled half power beam width (HPBW) and flrst null beam width (FNBW). HPBW and FNBW of a uniformly excited antenna array with similar size and main beam directions are chosen as the beam width constraints in each case. Algorithms are applied to determine the non-uniform excitation applied to each element. The efiectiveness of the proposed algorithms for optimization of antenna problems is examined by all six sets of antenna conflgurations. Simulation results obtained in each case using both the algorithms are compared in a statistically signiflcant way. Obtained results using flre ∞y algorithm shows better performances than that of artiflcial bees colony optimization technique provided that the same number of function evaluations has been considered for both the algorithms.
115 citations
TL;DR: Three difierent structures of UWB antennas using clothing materials and suitable for wearable application were fabricated and presented and good agreement was observed.
Abstract: Communication technology is increasingly pervading everyday life. The rapid progress in wireless communication besides the increasing interest in wearable antennas and electronics in civil, medical, sport wear and military domains promises to replace wired- communication networks in the near future in which antennas are in more important role. Recently, there has been growing interest in the antenna community to merge between wearable systems technology, Ultra-Wideband (UWB) technology and textile technology. All these together have resulted in demand for ∞exible fabric antennas, which can be easily attached to a piece of clothing. In this paper, three difierent structures of UWB antennas using clothing materials and suitable for wearable application were fabricated and presented. The substrate of the designed antennas was made from jeans textile material, while radiating element and ground plane are made out of copper tape. The operating frequency of all three designs is between 3GHz and 12GHz. Measured results are compared with simulations and good agreement was observed.
111 citations
TL;DR: In this paper, the authors explored the application of information obtained from fully polarimetric data for land cover classiflcation and applied various decomposition techniques, such as minimum distance, maximum likelihood, parallelepiped and unsupervised: Wishart.
Abstract: The intent of this paper is to explore the application of information obtained from fully polarimetric data for land cover classiflcation. Various land cover classiflcation techniques are available in the literature, but still uncertainty exists in labeling various clusters to their own classes without using any a priori information. Therefore, the present work is focused on analyzing useful intrinsic information extracted from SAR observables obtained by various decomposition techniques. The eigenvalue decomposition and Pauli decomposition have been carried out to separate classes on the basis of their scattering mechanisms. The various classiflcation techniques (supervised: minimum distance, maximum likelihood, parallelepiped and unsupervised: Wishart) were applied in order to see possible difierences among SAR observables in terms of information that they contain and their usefulness in classifying particular land cover type. Another important issue is labeling the clusters, and this work is carried out by decision tree classiflcation that uses knowledge based approach. This classifler is implemented by scrupulous knowledge of data obtained by empirical evidence and their experimental validation. It has been demonstrated quantitatively that standard polarimetric parameters such as polarized backscatter coe-cients (linear, circular
81 citations
TL;DR: In this article, a simple hybrid measurement and electromagnetic modeling approach for the estimation of power returns from targets located behind walls in various through-the-wall radar imaging (TWRI) scenarios is discussed.
Abstract: In this paper, measured results for complex permittivity of some commonly used building walls under difierent hydration (wetness) levels are presented and a simple hybrid measurement and electromagnetic modeling approach for the estimation of power returns from targets located behind walls in various through-the-wall radar imaging (TWRI) scenarios is discussed. The radar cross section (RCS) of some typical targets of interest, such as an AK47 assault ri∞e and human, are flrst investigated in free-space using numerical electromagnetic modeling. A modifled radar range equation, which analytically accounts for the wall efiects, including multiple re∞ections within a given homogeneous or layered wall, is then employed in conjunction with wideband measured parameters of various common wall types, to estimate the received power versus frequency from modeled targets of interest. The proposed technique, which can be helpful in TWRI dynamic-range system design consideration, is, in principle, applicable to both bistatic and monostatic operations. The results for various wall types, including drywall, brick, solid concrete, and cinder block, the latter two under both wet and dry conditions, are presented.
76 citations
TL;DR: An advanced tracking procedure has been developed to deal with noisy modes, non-continuous behavior of eigenvalues, mode swapping etc.
Abstract: A new method for tracking characteristic numbers and vectors appearing in the Characteristic Mode Theory is presented in this paper. The challenge here is that the spectral decomposition of the moment impedance-matrix doesn't always produce well ordered eigenmodes. This issue is addressed particularly to flnite numerical accuracy and slight nonsymmetry of the frequency- dependent matrix. At speciflc frequencies, the decomposition problem might be ill-posed and non-uniquely deflned as well. Hence an advanced tracking procedure has been developed to deal with noisy modes, non-continuous behavior of eigenvalues, mode swapping etc. Proposed method has been successfully implemented into our in-house Characteristic Mode software tool for the design of microstrip patch antennas and tested for some interesting examples.
61 citations
TL;DR: Visual and quantitative analysis shows, that the proposed technique performs better compared to fusion scheme based on Contourlet Transform (CNT), as well as various quantitative measures like Mutual Information (MI), Spatial Frequency (SF), and Entropy (EN).
Abstract: The motivation behind fusing multimodality, multi- resolution images is to create a single image with improved interpretability. In this paper, we propose a novel multimodality Medical Image Fusion (MIF) method, based on Ripplet Transform Type-I (RT) for spatially registered, multi-sensor, multi-resolution medical images. RT is a new Multi-scale Geometric Analysis (MGA) tool, capable of resolving two dimensional (2D) singularities and representing image edges more e-ciently. The source medical images are flrst transformed by discrete RT (DRT). Difierent fusion rules are applied to the difierent subbands of the transformed images. Then inverse DRT (IDRT) is applied to the fused coe-cients to get the fused image. The performance of the proposed scheme is evaluated by various quantitative measures like Mutual Information (MI), Spatial Frequency (SF), and Entropy (EN) etc. Visual and quantitative analysis shows, that the proposed technique performs better compared to fusion scheme based on Contourlet Transform (CNT).
54 citations
TL;DR: In this paper, the diurnal and seasonal variation of surface refractivity over Nigeria was studied using four years in-situ meteorological data from eight location over Nigeria, and the results showed that the seasonal variation is basically a function of local meteorology.
Abstract: The diurnal and seasonal variation of surface refractivity over Nigeria was studied using four years in-situ meteorological data from eight location over Nigeria. At all the stations studied, it was observed that the diurnal refractivity variation was caused majorly by the dry term in the rainy season and the wet term is the major cause of refractivity variation in dry season except Sokoto and Jos. In Sokoto the result was found to be opposite and it is attributed to the fact that in dry season the humidity is almost close to zero while in rainy season the pressure seems to be almost constant but the temperature ∞uctuates rapidly and consequently the humidity. The variation pattern in Jos is as observed because of the altitude (» 1000m above sea level). At this altitude pressure variation seems to be insigniflcant. The result also show that the surface refractivity generally have higher value during rainy season than dry season at all location studied. The result also show that the value of surface refractivity increases from arid region in the north to the coastal area in south. The result also show that the diurnal refractivity variation is basically a function of local meteorology and while seasonal variation is caused follows the climatic condition.
48 citations
TL;DR: In this article, the localized surface plasmon resonances (LSPR) of a pair of dielectric-core/silver-shell nanospheres, with and without a silver nanobar connecting them, were investigated using the flnite element method.
Abstract: We investigate the localized surface plasmon resonances (LSPR) of a pair of dielectric-core/silver-shell nanospheres, with and without a silver nanobar connecting them, for difierent values of the permittivity of the dielectric core, using the flnite element method. Results show that the structure of a pair of core shells with a nanobar possesses a distinct blue-shifted behavior that can be manipulated from near infrared to visible light. The near fleld intensity can be enhanced by several orders of magnitude, and the working wavelengths depend on the shell thickness, dielectric medium in hollow metallic shell and the diameter of the nanobar. In addition, three or more pairs of nanospherical chain waveguides have also been investigated in our simulations.
48 citations
TL;DR: The bandwidth of the fully digital transmitter is increased 8 times using parallel processing time-interleaved architecture, while maintaining the same signal quality, in this paper.
Abstract: This paper presents a development of a wideband delta- sigma modulator for fully digital GHz transmitters. The fully digital RF transmitter is developed as a promising solution for software deflned radio (SDR) terminals and applications. The fully digital transmitter consists of a delta-sigma modulator, a high- speed multiplexer and a switching-mode power amplifler. The speed limitation of delta-sigma modulator is the main limitation to increase the signal bandwidth in fully digital transmitters. In this paper, the bandwidth of the fully digital transmitter is increased 8 times using parallel processing time-interleaved architecture, while maintaining the same signal quality. This architecture was implemented on FPGA and tested for difierent standards (WiMAX and LTE) with a signal bandwidth up to 8MHz. The concept was assessed in terms of SNDR by using a difierential logic analyzer at the output of FPGA, and the SNDR was found to be around 60dB.
TL;DR: In this article, a Z-R relation is derived using a data set which consists of nine rain events selected from Singapore's drop size distribution using two methods: the Gamache-Houze method, a simple threshold technique, and the Atlas-Ulbrich method.
Abstract: A Z-R relation is derived using a data set which consists of nine rain events selected from Singapore's drop size distribution. Rain events are separated into convective and stratiform types of rain using two methods: the Gamache-Houze method, a simple threshold technique, and the Atlas-Ulbrich method. In the Atlas-Ulbrich method, the variability of the rain integral parameters R; Z, Nw, D0 and gamma model parameter " are used for the classiflcation of rain into convective, stratiform and transition. Z-R relations are derived for each type of rain after classiflcation. The changes in the coe-cients of the Z-R relations for difierent rain events are plotted and analyzed. The Z-R relations of the difierent methods using the Singapore data are compared and analyzed. It is concluded that the coe-cient A of the Z-R relation is higher for the convective stage followed by the stratiform and transition stages. The coe-cient b values are higher for the transition stage followed by the stratiform and convective stages. Re∞ectivities are extracted from RADAR data above NTU site for rain events and compared with the re∞ectivities derived from the distrometer data. Rain rates retrieved from RADAR data using the proposed relations from Singapore's data set are compared with the distrometer rain rates. The RADAR extracted rain rates are found to be constantly lower than the distrometer derived rain rates but matches well.
TL;DR: In this paper, the authors presented formulas for the central and remote expansions and for the coe-cients of the zonal harmonics (source constants) in the case of general axisymmetric electrodes and dielectrics.
Abstract: The electric potential and fleld of an axially symmetric electric system can be computed by expansion of the central and remote zonal harmonics, using the Legendre polynomials. Garrett showed the usefulness of the zonal harmonic expansion for magnetic fleld calculations, and the similar radial series expansion has been widely used in electron optics. In this paper, we summarize our experience of using the zonal harmonic expansion for practically interesting axisymmetric electric fleld computations. This method provides very accurate potential and fleld values, and it is much faster than calculations with elliptic integrals. We present formulas for the central and remote expansions and for the coe-cients of the zonal harmonics (source constants) in the case of general axisymmetric electrodes and dielectrics. We also discuss the general convergence properties of the zonal harmonic series (proof, rate of convergence, and connection with complex series). Practical considerations about the computation method are given at the end. In our appendix, one can flnd many useful formulas about properties of the Legendre polynomials, various derivatives of the zonal harmonic functions, and a simple numerical integration algorithm.
TL;DR: This paper presents an optimization method based on an improved variant of one of the most powerful real parameter optimizers of current interest, called Difierential Evolution (DE), and designs a large multiple concentric planar thinned circular ring arrays of uniformly excited isotropic antennas.
Abstract: Circular antenna array design is one of the most important electromagnetic optimization problems of current interest. The problem of designing a large multiple concentric planar thinned circular ring arrays of uniformly excited isotropic antennas is considered in this paper. This antenna must generate a pencil beam pattern in the vertical plane along with minimized side lobe level (SLL). In this paper, we present an optimization method based on an improved variant of one of the most powerful real parameter optimizers of current interest, called Difierential Evolution (DE). Two sets of difierent cases have been studied here. First set deals with thinned array design with the goal to achieve number of switched ofi elements equal to 220 or more. The other set contains design of array while maintaining side lobe level (SLL) below a flxed value. Both set contains two types of design, one with uniform inter-element spacing flxed at 0.5‚ and the other with optimum uniform inter-element spacing. The half-power beam width of the synthesized pattern is attempted to maintain flxed at the value equal to that of a fully populated array with uniform spacing of 0.5‚. Simulation results of the designed thinned arrays are compared with a fully populated array for all the cases to illustrate the efiectiveness of our proposed method.
TL;DR: In this paper, the authors presented EpsiMu, a tool for dielectric properties measurement of porous or granular materials, which consists of a coaxial cell and dedicated software that can reconstruct the permittivity in almost real-time by de-embedding process.
Abstract: The principal aim of this article is the presentation of EpsiMu, a tool for dielectric properties measurement. This general tool can be used to characterize all types of materials, but in this article we apply it to porous or granular materials. The tool consists of a coaxial cell and dedicated software that allow us to reconstruct the permittivity in almost real-time by a de-embedding process. Dielectric permittivity of soils sample was measured using this microwave tool. So, we can then determine the relationship between the dielectric properties and volumetric water content µ of Fontainebleau sand (center of France) and Dune of Pilat sand (Arcachon Bay area, France). The clay efiect on Fontainebleau sand is also studied. We discuss the usefulness of several models that link the permittivity to volumetric water content of soil. It is shown that the soil permittivity model is not directly applicable to Fontainebleau sand and Dune of Pilat sand. We flnd a good match between our results representing the relative permittivity "r versus the volumetric water content µ and the Complex Refractive Index model (CRIM) between 600MHz and 1GHz. Alternative regression formulae are proposed. The implication of the determination of volumetric water content, µ, is discussed. A linear relation between the dielectric loss tangent and volumetric water content µ of soils is established.
TL;DR: In this article, a coplanar waveguide (CPW) fed ultra-wideband (UWB) antenna with a notch band characteristic is presented, and the radiation patch of the proposed UWB antenna is designed using cantor set fractal technology.
Abstract: A coplanar waveguide (CPW) fed ultra-wideband (UWB) antenna with a notch band characteristic is presented in the paper. The radiation patch of the proposed UWB antenna is designed using cantor set fractal technology. The bandwidth is broadened by setting two symmetrical triangular tapered corners at the bottom of the wide slot of the proposed UWB antenna. The notched band characteristic is achieved by employing a T-shaped tuning stub at the top of the wide slot. The notched band can be controlled by adjusting the length and the width of the T-shaped tuning stub to give tunable notched band function. The proposed cantor set fractal wide slot UWB antenna has been designed in details and optimized. Experimental and numerical results show that the proposed antenna, with compact size of 26 £ 21mm 2 , has an impedance bandwidth range from 2.8GHz to 11GHz for voltage standing-wave ratio (VSWR) less than 2, except the notch band frequency 5.0GHz{6.3GHz for HIPERLAN/2 and IEEE 802.11a (5.1GHz{5.9GHz).
TL;DR: In this article, the authors proposed a new method, retrieved results and validation for complex and frequency dependent permittivity and permeability parameter extraction of two composite, homogeneous and isotropic magnetically loaded microwave absorbers.
Abstract: This work presents new method, retrieved results and validation for complex and frequency dependent permittivity and permeability parameter extraction of two composite, homogeneous and isotropic magnetically loaded microwave absorbers. Permittivities and permeabilities are extracted from free space transmission measurements for frequencies from 22 up to 140GHz. For validation of the results re∞ection measurements (samples with and without metal backing) are performed and are compared with simulations that use extracted models. The proposed new method solves some shortcomings of the popular methods: extracts both permittivity and permeability only from transmission parameter measurements, gives good results even with noisy data, does not need initial guesses of unknown model parameters.
TL;DR: A novel design of Butler matrix in substrate integrated waveguide (SIW) technology with wide frequency band characteristics and potential use of this sub-system in multibeam antenna design is discussed.
Abstract: This paper introduces a novel design of Butler matrix in substrate integrated waveguide (SIW) technology with wide frequency band characteristics. Butler matrices are particularly useful in advanced antenna design and characteristics such as wideband operation, power handling, manufacturing, integration, cost, etc. are typical issues to be addressed in many applications. The proposed planar 4 £ 4 Butler matrix provides an interesting solution to most of these issues. Wideband operation is achieved thanks to improved cross-couplers. These components are also characterized by higher power handling when compared to E-plane couplers. The use of SIW technology enables to reduce insertion losses compared to other printed technologies, while maintaining most advantages of such technologies such as high integration, manufacturing simplicity, low weight, etc. The proposed design is fully described, from the elementary building blocks to the full assembly performances. The design is optimized for operation in Ku-band with a center frequency at 12.5GHz. A prototype of the 4 £ 4 Butler matrix is manufactured, and good performances are conflrmed over 24% relative frequency bandwidth. Potential use of this sub-system in multibeam antenna design is also discussed.
TL;DR: In this article, a simple and realistic approach has been demonstrated for better estimation of rain attenuation using Ku-band signal propagation data and ground rain rate measurements at Kolkata, India.
Abstract: Rain attenuation is an important aspect of signal propagation above 10GHz frequency. The attenuation time series generation from point rain rate measurement is crucial due to unavailability of actual signal measurements. In this paper, a simple and realistic approach has been demonstrated for better estimation of rain attenuation using Ku-band signal propagation data and ground rain rate measurements at Kolkata, India. The ITU-R model of rain attenuation has been modifled by incorporating an efiective slant path model. The efiective slant path has been estimated and modelled in terms of a power-law relationship of rain rate data of 2007{2008. The methodology has been validated with the measured data of 2006. Comparison with ITU-R and SAM clearly demonstrates the improved predictability of the proposed model at the present tropical location.
TL;DR: The investigated singleband Dicke radiometer showed significantly improved sensitivity of measured temperatures and merits further investigation to determine methods of protecting the radiometer for amplifier first front ends.
Abstract: We have investigated the possibility of building a singleband Dicke radiometer that is inexpensive, small-sized, stable, highly sensitive, and which consists of readily available microwave components. The selected frequency band is at 3.25-3.75 GHz which provides a reasonable compromise between spatial resolution (antenna size) and sensing depth for radiometry applications in lossy tissue. Foreseen applications of the instrument are non-invasive temperature monitoring for breast cancer detection and temperature monitoring during heating. We have found off-the-shelf microwave components that are sufficiently small (< 5 mm × 5 mm) and which offer satisfactory overall sensitivity. Two different Dicke radiometers have been realized: one is a conventional design with the Dicke switch at the front-end to select either the antenna or noise reference channels for amplification. The second design places a matched pair of low noise amplifiers in front of the Dicke switch to reduce system noise figure.Numerical simulations were performed to test the design concepts before building prototype PCB front-end layouts of the radiometer. Both designs provide an overall power gain of approximately 50 dB over a 500 MHz bandwidth centered at 3.5 GHz. No stability problems were observed despite using triple-cascaded amplifier configurations to boost the thermal signals. The prototypes were tested for sensitivity after calibration in two different water baths. Experiments showed superior sensitivity (36% higher) when implementing the low noise amplifier before the Dicke switch (close to the antenna) compared to the other design with the Dicke switch in front. Radiometer performance was also tested in a multilayered phantom during alternating heating and radiometric reading. Empirical tests showed that for the configuration with Dicke switch first, the switch had to be locked in the reference position during application of microwave heating to avoid damage to the active components (amplifiers and power meter). For the configuration with a low noise amplifier up front, damage would occur to the active components of the radiometer if used in presence of the microwave heating antenna. Nevertheless, this design showed significantly improved sensitivity of measured temperatures and merits further investigation to determine methods of protecting the radiometer for amplifier first front ends.
TL;DR: The proposed processor termed as Forward Automatic Order Selection Ordered Statistics Detector (FAOSOSD) does not require any prior information about the number of interfering targets and aims to improve the Ordered statistics Constant False Alarm Rate detector performance under severe interference situations.
Abstract: This paper proposes a new approach for e-ciently determining the unwanted interfering samples in the reference window, for the ordered statistics constant false alarm rate detector, based on the application of the information theoretic criteria principle. The proposed processor termed as Forward Automatic Order Selection Ordered Statistics Detector (FAOSOSD) does not require any prior information about the number of interfering targets. The proposed design aims to improve the Ordered Statistics Constant False Alarm Rate detector performance under severe interference situations. The number of interfering targets is obtained by minimizing the information theoretic criteria. Simulation results that illustrate the performance of the proposed method versus the classical OS-CFAR, the AND-CFAR and the OR-CFAR detectors are presented and discussed.
TL;DR: In this article, a study of the raindrop size distribution along the eastern coast of South Africa (Durban) is presented, where the best kernel estimator, which results in the lowest integral square error (ISE), is used to measure the closeness of the estimated lognormal and gamma pdf of rain drop size to the measured raindrop distribution.
Abstract: A study of the raindrop size distribution along the eastern coast of South Africa (Durban) is presented. The Biweight kernel estimator based on distometer measurement is used to determine the best estimate of the measured raindrop size probability distribution function (pdf). The best kernel estimator, which results in the lowest integral square error (ISE), is used to measure the closeness of the estimated lognormal and gamma pdf of raindrop size to the measured raindrop size distribution. It is established that the optimised lognormal pdf slightly outperforms the optimised gamma pdf in terms of the mean ISE and the RMSE values, with mean ISE values of 0.026 for lognormal and 0.04 for gamma distributions, respectively, and corresponding mean RMSE values of 0.073 and 0.081, respectively. The method-of-moments gamma and lognormal distributions are observed to be worse estimators of the measured pdf than the two optimized distributions. The N(D) distributions using the optimised lognormal and gamma distributions for the region are compared with those for difierent tropical regions, namely, India, Singapore, Nigeria, Indonesia, and Brazil. While the Indian lognormal N(D) model gives the highest peak for low raindrop sizes for all rain rates, Durban's gamma and lognormal models exhibit the widest raindrop size spread over all rain rates ranging from 1{120mm/h. Finally, the speciflc attenuation due to rain using the Durban models are compared against the ITU-R models and actual measurements over a 19.5GHz LOS link; the results indicate a need for further work involving both distrometer and radio link measurements for rain rates exceeding 30mm/h in the eastern coast of South Africa.
TL;DR: In this paper, a low-loss passive metamaterial exhibiting negative refractive index or double negative electromagnetic properties at microwave frequencies is proposed, which is a lattice of spherical particles made up of multiple dielectric materials in concentric layers.
Abstract: A low-loss passive metamaterial exhibiting negative refractive index or “double negative” electromagnetic properties at microwave frequencies is proposed. The metamaterial is a lattice of spherical particles made up of multiple dielectric materials in concentric layers. Because no magnetic constituents (that tend to have higher losses) are involved, the negative-index behavior is possible with very low values of attenuation. A negative-index metamaterial based on dielectric-coated metal spheres is also proposed, and is predicted to have lower attenuation than other structures based on metallic scatterers. Numerical results and design principles are given.
TL;DR: The beamspace domain of parasitic antenna arrays is explored, providing the aerial degrees of freedom available for use in Multiple Input-Multiple Output (MIMO) systems and the multiplexing capability of ESPAR antennas is presented as a means for supporting future performance demanding communication systems.
Abstract: The beamspace domain of parasitic antenna arrays is explored in this paper, providing the aerial degrees of freedom available for use in Multiple Input-Multiple Output (MIMO) systems. The beamspace representation allows for the design of an alternative MIMO architecture based on single radio-frequency (RF) chains, and facilitates the inclusion of MIMO transceivers in devices with strict size limitations. A three dimensional orthogonal expansion is performed on the beamspace domain providing the basis patterns used for mapping of the transmitted symbols and for sampling at the receiver. The expansion is based on the Gram-Schmidt orthonormalization procedure and can be generalized for any parasitic antenna array. The multiplexing capability of ESPAR antennas is presented as a means for supporting future performance demanding communication systems. Performance evaluation results are illustrated in detail.
TL;DR: In this paper, a new compact UWB monopole antenna with dual band rejection is presented, which is designed using FR4 substrate with dielectric constant 4.4, loss tangent 0.02 and a height of 1.59mm.
Abstract: In this communication, a new compact UWB monopole antenna with dual band rejection is presented. The antenna is designed using FR4 substrate with dielectric constant 4.4, loss tangent 0.02 and a height of 1.59mm. Initially the UWB antenna is designed to obtain a 153% fractional bandwidth from 2.4GHz{21.7GHz. The ground plane beneath the patch is etched out and a rectangular slot is introduced to obtain a broadband matching over the operating frequency range. Later the antenna is modifled to get a frequency notch in the IEEE802.11a and HIPERLAN/2 WLAN operating band (5.15GHz{5.825GHz) to avoid potential interference. A U shaped slot is optimally introduced in the patch to get the desired performance. Finally an L shaped slot is cut from the radiating patch to fllter the frequency band 3.3GHz{3.6GHz, which is WiMAX service band. The antenna parameters are optimized and the efiects of parametric variation on antennas performance are studied and the summary is presented. The antenna is fabricated and measured results are presented. The measured results are in well agreement with the simulated results.
TL;DR: In this article, the magnetic energy minimum in a system of perfect, or ideal, conductors is shown to be minimized when the current distribution is a surface current density with zero interior magnetic fleld; perfect conductors are perfectly diamagnetic.
Abstract: We prove a theorem on the magnetic energy minimum in a system of perfect, or ideal, conductors. It is analogous to Thomson's theorem on the equilibrium electric fleld and charge distribution in a system of conductors. We flrst prove Thomson's theorem using a variational principle. Our new theorem is then derived by similar methods. We flnd that magnetic energy is minimized when the current distribution is a surface current density with zero interior magnetic fleld; perfect conductors are perfectly diamagnetic. The results agree with currents in superconductors being conflned near the surface. The theorem implies a generalized force that expels current and magnetic fleld from the interior of a conductor that loses its resistivity. Examples of solutions that obey the theorem are presented.
TL;DR: Simulation results of applying the dynamic thinning technique to linear and planar arrays and evaluation of the objective function in such cases requires large computational resources, thus reducing the rate of convergence.
Abstract: Thinning is a technique by which the total number of active elements in an antenna array is reduced without causing major degradation in system performance. Dynamic thinning is the process of achieving this under real time conditions. Stochastic techniques have been useful in the design of thinned arrays. However while applying the technique to large 2-D arrays, under changing conditions problems arise due to the very large and rugged solution space. Also, evaluation of the objective function in such cases requires large computational resources, thus reducing the rate of convergence. This paper suggests a technique using Genetic Algorithm which is useful for overcoming these problems. After discussing the basic concept involving dynamic thinning and application methodology, simulation results of applying the technique to linear and planar arrays are presented.
TL;DR: Compared with the continuous realization and subsequent quantization, experimental results indicate better performance of the discrete realization of the phase-excitation value of the proposed algorithm.
Abstract: The reconfigurable design problem is to find the element that will result in a sector pattern main beam with side lobes. The same excitation amplitudes apply to the array with zero-phase that should be in a high directivity, low side lobe pencil shaped main beam. Multi-beam antenna arrays have important applications in communications and radar. This paper presents a new method of designing a reconfigurable antenna array with quantized phase excitations using a new evolutionary algorithm called differential evolution (DE). In order to reduce the effect of mutual coupling among the antenna-array elements, the dynamic range ratio is minimized. Additionally, compared with the continuous realization and subsequent quantization, experimental results indicate better performance of the discrete realization of the phase-excitation value of the proposed algorithm.
TL;DR: In this article, the authors studied radar cross sections of clutter estimated by approximate models in the HF-VHF bands in a bistatic conflguration, where transmitter and receiver are dissociated.
Abstract: HF-VHF Radars are used in oceanography and sea surveys (1) because they can cover a larger distance than other radars. We can use this kind of radar in sea and ground environments. In these bands, phenomena associated with clutter (2) interfere with radar performance for ship and terrestrial vehicle detection. To improve radar performance, a measure called Radar Cross Section is calculated. We have studied Radar Cross Section in HF-VHF bands with the objective of determining the in∞uence of sea and ground clutter. There are two categories of Radar Cross Section: exact methods (3) and approximate methods (4{8). We have studied approximate methods because they are faster than exact methods. A common radar conflguration is the bistatic conflguration where transmitter and receiver are dissociated. The aim of this paper is to study Radar Cross Sections of clutter estimated by approximate models in HF-VHF bands in a bistatic conflguration.
TL;DR: In this paper, the results of the estimation of uncertainty for some of the most common EMC tests, such as: the measurement of radiated and conducted emissions according to CISPR 22 and radiated (IEC 61000-4-3) and conducted immunity, using both the conventional techniques of the Guide to the Expression of Uncertainty in Measurement (GUM) and the Monte Carlo Method.
Abstract: The rigorous uncertainty estimation in Electromagnetic Compatibility (EMC) testing is a complex task that has been addressed through a simplified approach that typically assumes that all the contributions are uncorrelated and symmetric, and combine them in
a linear or linearized model using the error propagation law. These assumptions may affect the reliability of test results, and therefore, it is advisable to use alternative methods, such as Monte Carlo Method (MCM), for the calculation and validation of measurement uncertainty. This paper presents the results of the estimation of uncertainty for some of the most common EMC tests, such as: the measurement of radiated and conducted emissions according to CISPR 22 and radiated (IEC 61000-4-3) and conducted (IEC 1000-4-6) immunity, using both the conventional techniques of the Guide to the Expression of Uncertainty in Measurement (GUM) and the Monte Carlo Method. The results show no significant differences between the uncertainty estimated using the aforementioned methods, and it was observed that the GUM uncertainty framework slightly overestimates the overall uncertainty for the cases evaluated here. Although the
GUM Uncertainty Framework proves to be adequate for the particular EMC tests that were considered, generally the Monte Carlo Method has features that avoid the assumptions and the limitations of the GUM Uncertainty Framework.