This article presents a coplanar printed monopole antenna for digital television (DTV) in the UHF band (470-862 MHz) application. The antenna structure consists of a meander loop monopole for radiation, a step-shaped ground plane for impedance matching, and a 50-mini coaxial feedline for excitation. The meander loop monopole and step-shaped ground plane are printed on the same side of a substrate with an area of 15×170 mm². The measured impedance bandwidth for 2.5:1 voltage standing wave ratio (VSWR) is 550 MHz (465-1015 MHz, 74%), covering the DTV band. In addition, the proposed antenna shows a real reception performance on a notebook computer. The reception results for audio and video signals exhibit stable characteristics.

A circular polarization microstrip antenna with a single feeding point is designed in this paper. The microstrip patch has a structure of Koch fractal edges, and the circular polarization is realized by inspiring two degenerate modes that are orthogonal to each other. The software CST MWS^® is used to simulate the designed antenna. The simulation results indicate that circular polarization radiation could be achieved though feeding at one of the diagonal lines of the patch by a probe. Antennas considering substrate medium loss are also simulated, and the results are approximate to those with ideal substrates. According to the simulated results of the surface currents at the edges of the patch, an equivalent line current radiation model is proposed to describe the radiation characteristics of the designed antenna. A circular polarization microstrip antenna is fabricated and tested. The simulated, calculated, and the measured results agree well. The designed antenna operates at 1.575 GHz, with an impedance bandwidth of 3% for VSWR < 2, the gain of the antenna is 2.6 dB, and the axial ratio in the maximum radiation direction is 2.7 dB.

The influence of atmospheric gases and tropospheric phenomena becomes more relevant at frequencies within the THz band (100 GHz to 10 THz), severely affecting the propagation conditions. The use of radiosoundings in propagation studies is a well established measurement technique in order to collect information about the vertical structure of the atmosphere, from which gaseous and cloud attenuation can be estimated with the use of propagation models. However, some of these prediction models are not suitable to be used under rainy conditions. In the present study, a method to identify the presence of rainy conditions during radiosoundings is introduced, with the aim of filtering out these events from yearly statistics of predicted atmospheric attenuation. The detection procedure is based on the analysis of a set of parameters, some of them extracted from synoptical observations of weather (SYNOP reports) and other derived from radiosonde observations (RAOBs). The performance of the method has been evaluated under different climatic conditions, corresponding to three locations in Spain, where colocated rain gauge data were available. Rain events detected by the method have been compared with those precipitations identified by the rain gauge. The pertinence of the method is discussed on the basis of an analysis of cumulative distributions of total attenuation at 100 and 300 GHz. This study demonstrates that the proposed method can be useful to identify events probably associated to rainy conditions. Hence, it can be considered as a suitable algorithm in order to filter out this kind of events from annual attenuation statistics.

Maximizing the Radio Frequency Identication (RFID) performance is one of the main challenges in application domains, such as logistics and supply chain management, where the undesired effect of Tag collisions can significantly degrade the speed of the inventory process. The dominating UHF EPC Class-1 Generation-2 (EPC Gen2) protocol only specifies collision avoidance algorithms but makes no provision for collision resolution. In this paper, performance enhancement of the EPC Gen2 standard exploiting Tag collision recovery is demonstrated, for the first time, in real time with measurements. Three simple and effective approaches to handle successful Tag acknowledgments of recovered collided packets are proposed and implemented on a software-defined Reader and programmable Tags. The attained benefits over the conventional EPC Gen2 MAC scheme are significant: the throughput per time slot is increased by 72% while the overall time required to inventory the Tag population is reduced by 26%. The effectiveness of the proposed approach and the validity of the achieved results are confirmed by the good agreement with simulations reported in the literature.

Circular synthetic aperture radar (CSAR) imaging based on compressive sensing with random step frequency (RSF) as transmitted signal is introduced. CSAR is capable of obtaining both two-dimensional high resolution image and three-dimensional image due to a circular collection trajectory. RSF signal shares good characteristics of noise signals including ``thumbtack-shape" ambiguity function, low probability of interception, and strong anti-jamming capability. As a result, CSAR adopting RSF signal can make use of advantages of both CSAR and RSF signal. Compressive sensing is a new data acquisition and reconstruction theorem for sparse or compressible signals, which needs fewer samples to reconstruct signals than traditional Nyquist theorem. Simulation results show that both two-dimensional and three-dimensional targets can be well reconstructed from few samples by applying compressive sensing to RSF CSAR imaging.

In this article, a new hybrid algorithm based on Honey Bees Mating Optimization (HBMO) combined with the Tabu Search (TS) for null steering beamformer in adaptive antenna array is presented. The proposed method HBMO/TS is applied to a set of random cases to estimate the excitation weights of an antenna array that steer the main lobe towards a desired signal, place nulls towards several interference signals and achieve the lowest possible value of side lobe level. Moreover, the proposed algorithm is tested and compared with two other wellknown approaches that are the Least Mean Squares (LMS) and Genetic Algorithm (GA). The abovementioned methods have been performed considering uniform linear antenna array and achieved by controlling only the phase of each array element. Results obtained prove the effectiveness of our proposed approach HBMO/TS.

A multilayered backscattering model for a lossy medium has been presented in this paper. This multilayered model has been used to calculate the total surface reflection coefficients of a snow pack for both horizontal and vertical co-polarizations. The total surface reflection coefficients include contributions from both surface and volumetric backscattering. The backscattering coefficients calculated by this model were compared with in situ measurements on dry and wet snow. Results show that good agreements are obtained between the model and measurements for the co-polarization modes, especially for the snow with less liquid water content.

A parametric analysis is performed for a wideband Archimedean spiral antenna in recognition of an emerging concept to integrate RFID along with several applications by using a single antenna. The antenna is fabricated using state-of-the-art inkjet printing technology on various commercially available paper substrates to provide the low-cost, flexible RF modules for the next generation of "green" electronics. The effects on electromagnetic characteristics of the planar Archimedean spiral antenna, due to the use of paper are investigated besides other parameters. The proposed antenna is evaluated and optimized for operational range from 0.8-3.0 GHz. It exhibits exceptional coverage throughout numerous RFID ISM bands so do for other wireless applications.

Aiming to efficiently overcome the acoustic refraction and accurately reconstruct the microwave absorption properties in heterogeneous tissue, an iterative reconstruction method is proposed for microwave-induced thermo-acoustic tomography (MITAT) system. Most current imaging methods in MITAT assume that the heterogeneous sound velocity (SV) distribution obeys a simple Gaussian distribution. In real problem, the biological tissue may have several different inclusions with different SV distribution. In this case, the acoustic refraction must be taken into account. The proposed iterative method is consisted of an iterative engine with time reversal mirror (TRM), fast marching method (FMM) and simultaneous algebraic reconstruction technique (SART). This method utilizes TRM, FMM and SART to estimate the SV distribution of tissue to solve the phase distortion problem caused by the acoustic refraction effect and needs little prior knowledge of the tissue. The proposed method has great advantages in both spatial resolution and contrast for imaging tumors in acoustically heterogeneous medium. Some numerical simulation results are given to demonstrate the excellent performance of the proposed method.

In this paper, a numerical study based on the Finite Element Method (FEM) formulation of Ansoft's High Frequency Structure Simulator (HFSS) is reported to investigate the performance of a conformal Broadside Coupled Rectangular Split Ring Resonators (BC-SRR) of negative effective permeability around a resonant frequency of 1.27 GHz for non-linear polarization applications. The size of the BC-SRR is 15 mm x 15 mm x 0.8 mm on a polyimide substrate with a relative permittivity of 3.5 and a loss tangent of 0.004. The performance of the BC-SRR is characterized in terms of reflection and transmission spectra, effective relative permittivity and permeability, and the dispersion diagram for both flat and twisted profiles. The flat BC-SRR operates over the frequency range from 1.2615 to 1.2842 GHz. The twisted BC-SRR inclusions are investigated at 90°. It has been found that the resonant frequency is changed to 1.1064 GHz and bandwidth becomes from 1.08 GHz to 1.0537 GHz for the twisted profile. Moreover, it is found that the unit cell of the twisted BC-SRR profile is based on two BC-SRRs inclusions. Furthermore, it is found that the twisted profile exhibits negative relative permittivity and permeability simultaneously.

A novel two-dimensional elliptical lens monopulse antenna at millimeter-wave frequencies is presented using the technique of dielectric-filled parallel plates where TE₁₀ mode propagates. A cavity-backed aperture-coupled elliptical patch antenna array with sum/difference ports is located at the back of the elliptical lens as a feeding antenna. The lens antenna is designed, fabricated and tested at 35 GHz. Measurements show clean and symmetrical fan-beam patterns are realized for both the sum and the difference beams. The measured 3-dB E- and H-plane beamwidths of the sum pattern are 5.3° and 37°, respectively. A gain of 16.7 dBi is realized for the sum beam (86% radiation efficiency), while a deep null of -32.4 dB is achieved for the difference beam. In addition, a 10-dB impedance bandwidth of 7.1% is measured for both the sum and difference beams.

A compact coplanar waveguide (CPW)-fed printed monopole antenna comprising of two symmetrical C-shaped radiating elements, a parasitic E-shaped strip, and a truncated CPW ground for WLAN/WiMAX applications is proposed. By embedding a parasitic E-shaped strip inside the two symmetrical C-shaped radiating elements, four resonant frequencies and three operating bands are obtained. By etching two quarter-circles in the CPW ground, impedance matching condition of the third operating band is significantly improved. A prototype of the proposed antenna has been constructed and experimentally studied. The measured results show that three distinct operating bandwidths with 10 dB return loss are about 500 MHz (2.33-2.83 GHz), 700 MHz (3.27-3.97 GHz) and 2.37 GHz (4.3-6.67 GHz), covering all the 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX bands. Furthermore, the antenna has a simple planar structure and a small volume of only 31 × 21 × 1.6 mm³. Good radiation characteristics and acceptance peak realized gains are obtained over the operating bands.

In this paper, super-resolution imaging and negative refraction by a two-dimensional (2D) triangular lattices graded photonic crystal (GPC) were studied. The graded photonic crystal (GPC) was obtained by varying the radius in each row so that its effective refractive index changes along the transverse direction. By using Plane Wave Expansion (PWE) method and Finite-Difference Time-Domain (FDTD) method, we show that negative refraction and superlensing can be realized in the designed graded photonic crystal. Numerical simulations show that the photonic crystal structures and frequency have an impact on the resolution.

Koch-like fractal curve and Sierpinski Gasket are syncretized into a novel Sierpinskized Koch-like sided bow-tie (SKLB) multifractal in superior-inferior way. A K₄S₄ SKLB multifractal dipole fed by a linearly tapered microstrip Balun is designed, simulated, fabricated and measured. The well consistent results from measurement and experiment corroborate validity of design and the multifractal antenna's superiority and advantages over its monofractal counterparts in impedance, bandwidth, directivity, efficiency, and dimension. Six good matched bands(S₁₁ ≤ -10 dB) with moderate gain (2.12 dBi-9.55 dBi) and high efficiency (87%-97%) are obtained within band 1.5 GHz-14.5 GHz, of which f₁ = 1.92 GHz, f₂ = 3.94 GHz, and f₃ = 5.09 GHz are generally useful. The multibands are all almost omnidirectional or quasi-omnidirectional in H-plane (Phi=0°, XOZ) and doughnut-shaped or dented doughnut-shaped in E-plane (Phi = 90°, YOZ). So it is an attractive candidate for applications like PCS, IMT2000, UMTS, WLAN, WiFi, WiMAX and other fixed or mobile wireless multiband communication systems.

A novel branch-line coupler which can operate at two frequencies is presented in this paper. The proposed planar topology, which is different from the conventional one, is analyzed and designed. The new coupler maintains not only compact but also dual-band characteristics. The length of the proposed stepped-impedance lines can be adjusted flexible according to the required operation frequency. In order to verify the method, a dual-band micro-strip coupler operating at 0.9 and 2.1 GHz is fabricated and measured. The simulated and measured results show good agreements.

In this paper, an analytical solution is investigated for the twodimensional problem of electromagnetic scattering of a line source from a perfect electromagnetic conductor (PEMC) circular cylinder coated with an anisotropic media. In the anisotropic region, the relative permittivity and permeability tensors, when referred to principal axes (ρ, φ, z), are biaxial and diagonal. It is demonstrated that the relations of electromagnetic field vectors in anisotropic medium is equal to a PEMC boundary conditions when the parameters of the anisotropic region are chosen in an appropriate manner. Therefore, this region can act as a PEMC cylinder.

In this paper, a planar metallic nanostructure design, which supports two distinct Fano resonances in its extinction crosssection spectrum under normally incident and linearly polarized electromagnetic field, is proposed. The proposed design involves a circular disk embedding an elongated cavity; shifting and rotating the cavity break the symmetry of the structure with respect to the incident field and induce higher order plasmon modes. As a result, Fano resonances are generated in the visible spectrum due to the destructive interference between the sub-radiant higher order modes and super-radiant the dipolar mode. The Fano resonances can be tuned by varying the cavity's width and the rotation angle. An RLC circuit, which is mathematically equivalent to a mass-spring oscillator, is proposed to model the optical response of the nanostructure design.

The Doppler spectral characteristics of electromagnetic backscattered echoes from dynamic nonlinear surfaces of finite-depth sea is investigated with the second-order small-slope approximation (SSA-II). The revised nonlinear hydrodynamic choppy wave model (CWM) combining with an experiment-verified shoaling coefficient is utilized to model the finite-depth sea wave profiles, and the simulated surfaces of finite-depth sea show steeper crests and more flat troughs as depth decreases. First, Comparison of the Doppler spectra for linear sea surfaces and nonlinear choppy sea surfaces shows that nonlinear hydrodynamic effect greatly enhances the Doppler shift and the Doppler spectrum bandwidth, and the predicted results agree well with the rigorous numerical model data. The Doppler spectra of backscattered echoes from finite-depth sea with different depths are further evaluated. At small incident angles, the Doppler shifts and the spectra bandwidths are much lower for shallower sea, and the opposite situation can be gradually observed for increased incident angles. This indicates that the nonlinear wave-wave interactions among waves occur more frequently in finite-depth sea and the long waves will be suppressed while shorter wind waves will be boosted in shallower water. Moreover, the dependence of the Doppler spectral characteristics on polarization is also discussed.

A new technique for broadband material characterization, using a whispering-gallery-mode (WGM) resonator, is proposed. The resonant perturbation method is applied for the measurement of both the dielectric constant and loss tangent of various types of materials and over a wide frequency band. A comprehensive study on the reliability of using such technique, via simulations and measurements, is conducted as well. The feasibility of this device in sensing small variations of the dielectric properties of the material is investigated. Furthermore, the geometry of the resonator is slightly modified to fit liquid materials as well. This can be a promising solution for sensing human-body tissues or liquids such as blood or urine due to the sensitive nature of these resonators. The experimental setup is successfully utilized to measure the dielectric constant of a water droplet as a liquid sample as well as different material samples of arbitrary shapes and dielectric properties. The measurements are performed over the whole X- and K-bands where the obtained results are with a maximum deviation of only 3.3% for solids and 4.5% for liquids.

A modified ultra-wideband (UWB) printed rectangular antenna fed by a microstrip line is proposed. Overall dimension of the antenna is as compact as 14 (0.2 λ) × 14 (0.2 λ) × 1 mm3 where λ is the wavelength of the first resonance of the antenna. The main features of the proposed antenna are its compact size and its filtering characteristic over WLAN band. Through adjusting the dimensions of the elements of the antenna, notch frequency in different ranges of the UWB can be obtained. The resulting VSWR<1.5 impedance bandwidth is between 3.6-9.6GHz. Antenna presents a stable gain and omnidirectional radiation pattern in its operational frequencies.