This paper presents a design procedure for the generation of circular polarization (CP) from the composite right/left handed (CRLH) transmission line-(TL) with a coupled inter-digit structure and an inductive stub. The E_x and E_y components are generated from the parallel stubs and the fingers, respectively. The 90°-phase difference can be obtained by optimizing the dimension of the unit cell. In addition, the suitable amplitude ratio of |E_x| and |E_y| for CP generation is obtained by selecting a suitable position of the CRLH-TL between both edges of the ground. As a result, a CP with a measured bandwidth of 30.5% for an axial ratio (AR) of < 3 dB in the boresight direction is obtained. Using the behavior in both the left-handed (LH) and right-handed (RH) frequency regions, a scanning angle of the main beam of approximately 30° can be obtained by varying the frequency between 2.58 GHz and 2.99 GHz. Furthremore, the principle of CP generation is discussed.

Materials that exhibit negative refraction may have many novel applications. We seek to evaluate the possibility of soft-focusing of microwave signals using a medium with an indefinite (hyperbolic) anisotropic permittivity tensor. We fabricated a 147 mm thick and 220 mm wide Styrofoam sample with an embedded array of 12-gauge brass wires of 6.35 mm lattice spacing. Two single-loop antennas were used to approximately generate a transverse magnetic (TM) point source and the associated detector. Using an Agilent 8510C Vector Network Analyzer (VNA), the frequency spectrum was scanned between 7 and 9 GHz. Relative gain or loss measurements were taken at equal spatial steps behind the sample. A scanning robot was used for automatic scanning in the x, y, and z directions, in order to establish the focusing patterns. The signal amplitudes measured in the presence and absence of the sample were compared. The robot was controlled using LabVIEW¹, which also collected the data from the VNA and passed it to MATLAB² for processing. A soft focusing spot was observed when the antennas were placed in two different symmetric configurations with respect to the sample. These results suggest a method for focusing electromagnetic waves using negative refraction in indefinite (hyperbolic) anisotropic materials.

A Transverse Electromagnetic Mode (TEM) cell is one interesting alternative for studies of biological effects of radiofrequency radiation at reduced scale (in vitro studies). Controlled and well-characterized exposure conditions are essential for a concluding investigation: the biological sample has to be exposed to a uniform incident electromagnetic wave and the dose of absorbed radiation has to be precisely determined and correlated with the effect. Unfortunatelly, many times experimental dosimetry is either unavailable or unappliable, so that a pre-characterised and validated experimental set-up is mostly valuable. In this regard, the main objective of present work was to experimentally validate a computational model of an own-built TEM cell designed for bioelectromagnetic experiments in frequency range of 100MHz-1GHz. For validation, three significant parameters were investigated comparatively, by measurements and by computation: scattering parameters; incident electric field distribution; absorbed power in a set of liquid samples. By using the finite integration technique (FIT) method implemented by the commercial code CST Microwave Studio, and by using a vector network analyzer in the experimental approach, we validated the designed TEM cell and characterized it successfully. The second objective was a dosimetric study of four different liquid samples loaded in the cell. We used the absorption coefficient (AC) which may be assimilated to the specific absorption rate (SAR) of energy deposition in the whole sample volume. AC was shown to converge in experiment and simulation up to 800MHz for all samples. AC didn't depend directly upon sample's volume (even if, frequently, greater volumes showed higher absorption) but rather upon the internal field distribution in the sample, distribution that mostly depends on the frequency and on the dimensions of the liquid samples.

This paper investigates the spatial correlation characteristics of multiple antenna arrays deployed in wireless communication systems. First, we derive a general closed-form formula for the spatial correlation function (SCF) of a multiple antenna array with arbitrary array configuration under uniform signal angular energy distribution. Based on this formula, we then explore the characteristics of the SCF for several multiple antenna arrays with different array geometries. It is found that a multiple antenna array with a three-dimensional (3-D) array geometry can reduce the magnitude of its SCF and hence, improve the ergodic channel capacity (ECC) of wireless communication systems. Accordingly, we present a method to find the optimum 3-D antenna array geometry for maximizing the ECC of a wireless communication system. This method develops a novel objective function to incorporate with a particle swarm optimization (PSO) for solving the resulting optimization problem. Simulation results are provided for confirming the validity and the effectiveness of the proposed method.

We consider the performance analysis of natural frequency-based radar target recognition in the frequency domain. Based on the probability density function (PDF) of some quantity consisting of the projections of the frequency response onto the column spaces of the matrices constructed using the natural frequencies of the specific targets, we propose to analytically calculate the probability of the correct classification, where the PDF is obtained from the inverse Fourier transform of the characteristic function. The scheme is validated by comparing the performance using the analytic method with that using the Monte-Carlo simulation.

Compressed sensing (CS) has attracted significant attention in the radar community. The better understanding of CS theory has led to substantial improvements over existing methods in CS radar. But there are also some challenges that should be resolved in order to benefit the most from CS radar, such as radar signal with low signal to noise ratio (Low-SNR). In this paper, we will focuses on monostatic chaotic multiple-input-multiple-output (MIMO) radar systems and analyze theoretically and numerically the performance of sparsity-exploiting algorithms for the parameter estimation of targets at Low-SNR. The novelty of this paper is that it capitalizes on chaotic coded waveform to construct measurement operator incoherent with noise and singular value decomposition (SVD) to suppress noise. In order to improve the robustness of azimuth estimation, interpolation method is applied to construction of sparse bases. The gradient pursuit (GP) algorithm for reconstruction is implemented at Low-SNR. Finally, the conclusions are all demonstrated by simulation experiments.

Design and measurement results of a beam-steering integrated lens antenna at 77 GHz are presented. An 8-element LTCC aperture coupled patch antenna feed array with a switching network is used to electrically steer the main beam in H-plane. A 100-mm diameter Rexolite (ε_r = 2.53) lens is simulated and tested. The eccentricity of the lens is optimized in an earlier work with ray-tracing simulations for improved beam-steering properties compared to the conventional extended hemispherical and elliptical lenses. The beamsteering properties including scan loss, main-beam width and direction, side-lobe levels, directivity, and cross-polarization are analyzed in detail with both simulations and radiation pattern measurements. As expected, the results show that the side-lobe and cross-polarization levels are not predicted accurately with large feed offsets using the ray-tracing simulations. Nevertheless, it is shown that the lens shape can be successfully optimized with the simple and fast ray-tracing simulations. The measured half-power beam-width at 77 GHz is 2.5°±0.2° up to the largest tested beam-steering angle of 30°. The optimized eccentricity low permittivity lens results in smaller scan loss than the conventional lenses.

The use of permanent magnets as bearings has gained attention of researchers nowadays. The characteristics of forces and moments have to be analysed thoroughly for the proper design of permanent magnet bearings. This paper presents a mathematical model of an axially magnetized permanent magnet bearing (ring magnets) using Coulombian model and a vector approach to estimate the force, moment and stiffness. A MATLAB code is developed for evaluating the parameters. Furthermore, it is extended to analyse stacked ring magnets with alternate axial polarization. The proposed model is validated with the available literature. Comparison of force and stiffness results of the present model with the results of three dimensional (3D) finite element analysis using ANSYS shows good agreement. Finally, the cross coupled stiffness values in addition to the principal stiffness values are presented for elementary structures and also for stacked structures with three ring permanent magnets.

In this paper the concept of static electric permittivity and its measurement are discussed. A classical description of polarization via a harmonically bound charge model is revisited and the evolution of the polarization concept in the presence of free electrons is shown. Various electrostatic problems are defined under ideal conditions. The measurement procedures for characterizing the static permittivity of dielectrics and conductors via the measurement of induction-electric field, charge-potential difference and electrostatic energy variation are discussed. Two basic experiments with a lossy dielectric are described. In one case we reach an electrostatic equilibrium with an indeterminate solution. In the other case we define a magnetostatic problem. Finally, we comment on the case of a laboratory experiment remarking on the proper use of the low-frequency limit of dielectric constant and showing experimental results performed on a supercapacitor.

A novel radar energy control strategy based on an improved Interacting Multiple Model Particle Filter (IMMPF) tracking method is presented in this paper. Firstly, the IMMPF tracking method is improved by increasing the weight of the particle which is close to the system state and updating the model probability of every particle. Based on this improved IMMPF method, an energy control method for Low Probability of Intercept (LPI) is then presented, which controls the emission time and power of radar according to the target's range and radar cross section (RCS), under the condition of constant detection probability. The tracking accuracy and LPI performance are demonstrated in the Monte Carlo simulations. The results are validated through the comparisons with other methods.

In this paper we present a novel general methodology which ensure a minimum uncertainty in the measurement of the real part of the permittivity of a material measured using cylindrical shielded dielectric resonators. The method is based on the fact that for any given value of the dielectric permittivity there is an optimal radius of the cylindrical dielectric rod sample. When the dielectric rod sample has the optimum radius, the width of the coverage interval associated to the real part of the dielectric permittivity measurement result --- for a given confidence level --- is reduced due to a lower sensitivity of the dielectric permittivity to be measured versus the variations in the resonant frequency. The appropriated radius of a given sample under test is calculated using Monte Carlo simulations for a specific mode and a specific resonant frequency. The results show that the confidence interval could be reduced by one order of magnitude with respect to its maximum width predicted by the uncertainty estimation performed using the Monte Carlo method (MCM) as established by the supplement 1 of the Guide to the Expression of Uncertainty in Measurement (GUM). The optimum radius of the sample under examination is fundamentally determined by the electromagnetic equations that describe the measurement and does not depend specifically of the sources of uncertainty considered.

The purpose of this paper is to provide both qualitative and quantitative assessment of one of the methods for providing reliable transmission in the ZigBee system. After intensive research on the time delay spread in a variably loaded reverberation chamber, this facility was then used to measure the Packet Error Rate under multipath conditions ranging from an unloaded to an overloaded chamber case. In all measurements, the key parameter was the number of allowed packet repetitions (retries). Eventually, recommendations were given regarding the optimal use of retries and their impact on ZigBee performance under different multipath scenarios obtained in the reverberation chamber and related to particular propagation environments to which these conditions are typical.

A novel imaging technique based on a frequency scanning antenna array is presented. The method is conceived to provide angular information in range-based radar systems which do not allow mechanical or electronic beam steering. The beam steering is changed with the frequency, which requires a novel scattered field data processing scheme/algorithm to recover the SAR image. System features, advantages and limitations are discussed, presenting simulation and measurement results which show the system capabilities to resolve the range and angular position of the objects.

Due to growing importance of wireless access and the steeply growing data volumes being transported, the power consumption of wireless access networks will become an important issue in the coming years. This paper presents a model for this power consumption and investigates three base station types: macrocell, microcell, and femtocell base stations. Based on these models, the coverage effectiveness of the three base station types is compared and the influence of some power reducing techniques such as sleep modes and MIMO (Multiple Input Multiple Output) is evaluated.

In this paper, the RII depressed core triple clad based structure as Zero-dispersion Shifted optical fiber is optimized to obtain small pulse broadening factor (small dispersion and its slope) and low bending loss suitable for long haul communications. The proposed structures allow reducing the dispersion, its slope and the bending loss. The Genetic Algorithm (GA) and the Coordinate Descent (CD) technique are used for the optimization. The suggested design approach involves a special cost function which includes dispersion, its slope, and bending loss impacts. The proposed algorithm and structure have inherent potential to obtain large effective area and extend tolerance of bending loss simultaneously. Meanwhile, an analytical method is used to calculate the dispersion and its slope. In the meantime, the thermal stabilities of the designed structures are evaluated.

Novel designs of probe-fed broadband shorted patch antennas for ultrawideband (UWB) applications are presented in this paper. In these designs, unequal resonance arms fed by a folded patch produce multi resonances to broaden the impedance bandwidth. In the first design, the antenna consists of an asymmetric Eshaped patch, a folded-patch feed and shorting pins. This antenna is achieved by four adjacent resonances with the measured -10 dB impedance bandwidth of 76.18%. The pins are utilized to miniaturize the size of the patch. By introducing a folded ramp-shaped feed in the similar structure with the first design, a wider bandwidth with the five resonances is obtained. This improved design introduces an antenna with an impedance bandwidth of more than 110% and a considerable size reduction compared to the first antenna. The antennas present resonance tuning ability within the impedance bandwidth by varying the length of unequal arms. In addition, parametric studies are performed by investigating the effects of different key parameters on obtaining optimal designs of the proposed antennas.

This paper extends the existing transmission and capacity analysis in order to investigate the broadband potential of overhead high-voltage/broadband over power lines (HV/BPL) connections where a single repeater is additively deployed between their existing transmitting and receiving ends (overhead HV/BPL connections with two-hop repeater system). The contribution of this paper is three-fold. First, the broadband performance of various overhead HV/BPL connections with two-hop repeater system has been studied with regard to their cumulative capacity. The analysis and relevant simulations validate the potentially excellent communications medium of overhead HV/BPL channels over a 25 km repeater span well beyond 100 MHz in terms of cumulative capacity. In addition, through the deployment of two-hop repeater systems, apart from the upsurge of cumulative capacity, overhead HV/BPL connections become more adaptive to different capacity requirements. Second, it is found that overhead HV/BPL network capacity performance depends drastically on factors such as the overhead HV grid topology and the noise characteristics. Through the deployment of two-hop repeater systems, capacity losses due to existing aggravated overhead HV/BPL topologies and high noise environments are significantly reduced. Third, the numerical results reveal the importance of considering as suitable mitigation technique the deployment of overhead HV/BPL connections with two-hop repeater system. Except for the low-cost and quick technology upgrade of existing overhead HV/BPL networks, this mitigation technique may permit the future broadband exploitation of overhead HV/BPL networks and their interoperability with other broadband technologies.

A novel Koch fractal printed Yagi-Uda antenna fed by coplanar waveguide (CPW) is proposed and analyzed. The antenna has first-order Koch fractal monopoles, and the monopoles' ground plane acts as the ground plane of the antenna. The radiation characteristics of the antenna are simulated by CST Microwave Studio^® and explained by the simulated results. The antenna's currents distribution becomes more uniform after being fractal, which is conducive to increasing antenna's radiation directivity. The proposed Koch fractal Yagi-Uda antenna has an operating band of 885-913 MHz (relative bandwidth 3.1%) with the center frequency of 900 MHz. The total antenna size is 171 mm×85 mm (0.51λ×0.25λ) and the length in the antenna's polarization direction is only 25% of the wavelength corresponding to the center frequency. Compared to traditional Yagi-Uda antenna, the proposed antenna can achieve a 50% miniaturization effect.

This paper addresses the problem of designing statistical features for the extraction of building-up areas (BAs) from highresolution polarimetric synthetic aperture radar (PolSAR) imagery. The idea is to represent a building-up area by the distribution of its mid-level components, called intermediates, which are statistical patterns unsupervisedly learnt from PolSAR images. More precisely, by analyzing the structural properties and the polarimetric characteristics exhibited in various terrain types, we propose two kinds of midlevel features for small regions: the cluster based statistical feature (CSF) and the scattering mechanism based statistical feature (SMSF). In detail, for the CSF, the intermediates are the K-mean clusters with Wishart distance of the PolSAR images; for the SMSF, the intermediates are the scattering mechanism categories obtained by relying on a four-component decomposition with deorientation of the PolSAR images. In contrast with existing features for describing BAs, the proposed features, i.e., CSF and SMSF, capture more complex context information of BAs. We compare the proposed features with those based on the Gaussian Markov random field (GMRF) models, which have been proven to be suitable for BAs mapping. Experimental results on RADARSAT-2 datasets demonstrate the effectiveness of the proposed features.

A new high isolation lumped-element 180º hybrid, using electronically adjustable filters with varactor diodes, are proposed. This design is very simple and is based on only two configurable low order (N = 2) filters. Due to the limited tuning frequency range of varactor diodes, maximum near-octave frequency coverage of 2.5-5 GHz was planned in the high isolation hybrid. An impressive simulated typical isolation in the range of >60dB was achieved. One of the typical applications of developed hybrids could be the conversion of 70MHz IF to microwave frequencies, with broadband mixers in single-conversion converters, and with very high LO rejection (>60 dB).