This research article presents a compact planar antenna and a method for bandwidth improvement using parasitic resonant structure for UWB application with dual notch band performance, which are adjusted with an empirical formula. The radiating element of the microstrip square patch is slotted with two identical inverted J-shaped slots at the two non-radiating edges, a reversed F-shaped slot in the slotted radiating element, so that dual notch bands are excited. The bandwidth of the microstrip square patch radiator is improved with the help of a dumbbell-shaped parasitic resonant structure which is placed on the upper to partial ground plane for UWB application. The antenna, with size of (12×16 mm²), is fabricated on an epoxy FR-4 dielectric substrate of 1.6 mm thick and experimentally validated. The simulated and experimental results show that the invented radiator covers operating bandwidth from 2.8 to 13 GHz with VSWR < 2 and omnidirectional radiation characteristics. The two notch bands (3.3-4.2 and 5.1-5.4 GHz) are excited in the wide bandwidth by suppressing any interference from IEEE 802.16 WiMAX (3.3 GHz-3.6 GHz), C-band (3.7 GHz-4.2 GHz) and IEEE 802 11 a lower WLAN (5.15 GHz-5.482 GHz) with VSWR > 5.

In this paper, a folded slot active tag antenna for 5.8 GHz radio frequency identification (RFID) applications is presented. It consists of an inverted U-shaped monopole radiator fed by a coplanar waveguide (CPW) feed line and extended ground planes. A 10 dB return loss bandwidth of 5.65-6.55 GHz is achieved. The overall volume of the presented antenna is 10.7×11×1.6 mm³. A good agreement between the simulated and measured results is observed. The antenna has an omnidirectional radiation pattern at 5.8 GHz frequency which makes it suitable for RFID applications. It has advantages of compact dimensions and wider bandwidth than previously reported structures.

The deformation of antenna array due to external factors results in a significant degradation in the performance of the array direction of arrival (DOA) estimation. To solve this problem, an equivalent method based on the estimation of signal parameters by rotational invariance technique (ESPRIT) in single signal source for the array position errors is proposed in this paper. This method is mainly for the low-order deformation of the array and is based on the equivalent value of the position error. The DOA estimation of ESPRIT algorithm for single signal source was corrected. The simulation results show that the position error equivalent method can effectively equalize the position error caused by the vibration deformation of the array. When the equivalent position error is known, the orientation of the single signal source can be effectively corrected.

A frequency tunable multi-layer low cost microwave absorber is proposed for Ku and X bands of applications. The tunability is obtained with the cavity model design using two metallic layers; a frequency selective surface (FSS) layer and a metal backed substrate layer with the air gap between them. The change in air-gap results in variation of the effective substrate height, and as a consequences the resonant frequency is tuned. The coupling of LC resonance and cavity resonance at an air-gap of 7.5 mm results in a dual-band absorption of the design. The proposed absorber performance has been analyzed for both TE and TM polarizations of incident wave, and the results are found to be same. The studies on surface current distribution and incident angle variation are observed to get physical insight behind absorption. The waveguide measurement method is used to correlate the simulated results with the measured one. With this simple cost efficient design, the absorber appears well suited for EMI/ EMC application at X and Ku bands.

This paper presents an electronically tunable dual-band filtering power divider (TDFPD) with tuning diodes sharing technique. Two dual-mode tunable resonators (DMTRs) are embedded into a conventional power divider to achieve dual-band tunable bandpass filtering response. The two bands of the proposed TDFPD can be tuned independently. Tuning diodes sharing technique is utilized to reduce the number of tunable diodes. A prototype has been designed and fabricated to validate the proposed design as shown by the good agreement between the measured and simulated results. The measurement shows that the center frequencies of the lower and upper bands can be independently tuned from 1.31 to 1.62 GHz and 2.92 to 3.30 GHz, respectively. Within the passbands, isolation between the two output ports is higher than 16 dB with small phase and magnitude imbalance.

A multiple-arm dipoles antenna array based on magnetic coupling is proposed for ultra-high frequency (UHF) radio frequency identification (RFID) near-field applications. The design utilizes four multiple-arm dipoles to form a square region fed by a quarter-wave impedance transformer double-side parallel stripline (QDSPSL) structure. Broadband performance can be obtained for two different resonant frequencies caused by different dipole arm lengths. Moreover, in induction area, stronger and more uniform magnetic field distribution is generated for phases of currents on three dipole arms being kept in the same compared to conventional single-arm dipole. A 170 × 170 × 1.6 mm³ antenna has been fabricated on an FR-4 substrate to fit RFID near-field application. The measured 10-dB impedance bandwidth is 190 MHz (810-1000 MHz), which covers the entire UHF RFID frequency band (860-960 MHz). Measured tests on the antenna read range are carried out, exhibiting a reading region of 100 × 100 mm² and 100% reading rate within 200 mm for near-field tags.

Metallic pipelines are protected from induced corrosion by the application of coating and Cathodic Protection (CP) systems. The latter is achieved by keeping the pipeline at a constant Direct Current (DC) voltage in relation to the surrounding soil. While this is conventionally meant to arrest corrosion, the Alternating Current (AC) interference from high voltage transmission lines has been a major problem to the CP potential systems of buried steel pipelines. Several research studies dealing with this problem have been published, and a lot of research work is still on going. This work focuses on assessing the stability of the CP potentials under the influence of AC interference. Seven different CP potentials varying from -800 mV to -1200 mV were applied on steel pipe specimen exposed to the AC interference with a varying AC voltage from 0-50 V. The results of the laboratory investigation revealed that CP potential of -1150 mV was more stable under the influence of AC interference, with just a minimal shift from the set value. The results from the corrosion morphology tests on the pipelines using Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) reveal the need for optimising the CP potential to provide adequate or optimum protection to the pipelines. Thus, more research studies involving simulation and field studies may lead to a major breakthrough in improving protection potentials.

This paper focuses on the cognitive design of transmitting waveform to improve target detection capability in the presence of signal-dependent modulated jamming (e.g., chopping and interleaving (C&I) jamming). In particular, we reasonably assume that the modulation mode of signal-dependent jamming is available based on cognitive paradigm. The first design criterion is to minimize the integrated cross-correlation energy (ICE) between the transmitting waveform and jamming signal. In this way, the received jamming signal can be suppressed after matched filter processing is performed using the optimized waveform. The second design criterion is to minimize the integrated auto-correlation sidelobe level (IASL) for maintaining good range compression property. The practical constant modulus constraint is imposed on the transmitting waveform. Finally, to deal with the resulting non-convex problem, an iterative algorithm based on the majorization-minimization framework is developed. Numerical examples for specific signal-dependent modulated jammings are provided to demonstrate the effectiveness of the proposed methodology.

This paper aims to present two types of carbon nanotubes composite materials (CNTs-composite) for antenna applications within terahertz (THz) frequency band. These composite materials consist of CNTs coated by copper and silver, separately, to construct CNTs-copper and CNTs-silver composite materials, respectively. The comparisons between the dipole antennas of these structure materials with CNTs dipole antenna and copper dipole antenna are presented to exhibit performance evaluation of the presented new dipole antennas. The mathematical modeling of CNTs-composite material is presented in this paper. The results obtained from the comparisons CNTs-copper and CNTs-silver dipole antennas are presented based on S₁₁ parameters, gain and efficiency.

We investigated the potential application of planar chiral metamaterials (PCMs) to near infrared wavelength filters for multispectral measurement through electromagnetic simulation. PCM assumed here was a two-dimensional sub-wavelength surface grating on a high index film with chiral unit cells. The PCM exhibits optical activity (OA) for normally incident light at a finite wavelength range. Thus, by sandwiching the PCM with a pair of linear polarizers, a polarization interference-type BPF can be constructed. We focused on an all-dielectric PCM consisting of a silicon chiral layer and a dielectric underclad layer on a silica substrate. Wavelength filtering characteristics with different bandwidths have been verified for several underclad materials such as Si₃N₄, Al₂O₃, and Si.

We analyze relief graphene gratings by the coordinate transformation method (the C-method). This method is also used for analysis of multilayer gratings with graphene sheets at the interfaces. By using this method, we are able to obtain the eciency of deep graphene gratings with fast convergence rate while previous methods are limited to very shallow graphene gratings. Moreover, a terahertz polarizer is designed by relief graphene grating. Polarization extinction ratio and transmittance of single-layer and double-layer polarizer are simulated by the C-method. Double-layer polarizer gives extinction ratio from 22 dB to 10 dB over a frequency range of 1 GHz to 4 THz.

This work presents a design for a metasurface that provides near-unity electromagnetic energy harvesting and RF channeling to a single load. A metasurface and a feeding network were designed to operate at 2.72 GHz to deliver the maximum power to a single load. Numerical simulations show that the metasurface can be highly efficient delivering the maximum captured power to one load using a corporate feed network reaching Radiation-to-RF conversion efficiency as high as 99%. A prototype was fabricated incorporating a rectification circuit. Measurements demonstrated that the proposed metasurface harvester provides Radiation-to-DC conversion efficiency of more than 55%, which is significantly higher than earlier designs reported in the literature.

Hollow nanostructures based on the Fe_100-xCo_x alloy were synthesized in the pores of polymer template matrices based on PET using the electrochemical deposition method. Morphology, elemental composition, and structural features were characterized by scanning electron microscopy, energy dispersive analysis, and X-ray diffractometry. The study of the internal magnetic texture was carried out using Mossbauer spectroscopy. The dependence of the change in structural and magnetic properties from the atomic content of components in nanotube structure is revealed. It is established that the synthesized nanostructures are hollow Fe_100-xCo_x nanotubes with a body-centered cubic crystal structure. The decrease in the unit cell parameter with increasing cobalt concentration is due to the difference in the radii of Fe (1.227 Å) and Co (1.191 Å) atoms. It is established that a random distribution of magnetic moments directions of Fe atoms is observed for Fe₁₀₀Co₀ nanotubes. And magnetic texture along the nanotube axis is observed for Fe_100-xCo_x nanotubes, with an increase in Co atoms concentration. The average angle between the direction of the magnetic moment of iron atoms and the nanotube axis decreases from ϑ = 54.6˚ to ϑ = 24.5˚.

This paper presents a novel compact Wilkinson Power Divider (WPD) that improves harmonics suppression. The proposed WPD consists of a shunt open stub between two series similar inductors, and a microstrip line between an isolation resistor and each output port. This configuration acts as a low-pass filter with two transmission zeros. In addition, it facilitates manufacturability by using lower transmission line impedance values than conventional structures. Through Even and odd mode analysis, the general design equations have been derived in closed form. A 2 GHz microstrip WPD is designed, fabricated and measured based on the proposed technique. A great agreement has been obtained between the measured performance of fabricated WPD circuit and the simulation results. The measured results show that the second and third harmonic levels are about -47 dBc and -35 dBc, respectively. The proposed design has about 40% reduction in size better than conventional WPD. It achieves competing results compared to other published work.

Coherent Change Detection (CCD) is a powerful technique that uses Synthetic Aperture Radar (SAR) coherence to measure subtle ground changes in the imaged area. Unfortunately, the coherence estimator is biased for low coherence values, resulting in a highly degraded change detection performance. The spatial multilooking technique is typically used to improve coherence estimation but at the expense of spatial resolution. Actually, there are few SAR satellites that are able to deliver Multiple Look Complex (MLC) SAR images, which provide noticeable coherence bias reduction. In the present work, we investigate detection performance improvement that can be obtained through the use of MLC SAR images. The detection probability and false alarm are evaluated using experimental very high-resolution SAR data. After SAR image focusing and coherence estimation, the results indicate that the use of MLC SAR images with four looks allows for nearly 60% higher detection probability in the case of a low false alarm rate.

Solutions to the Maxwell equations for a planar non-integer dimensional perfect electric conductor (NID-PEC) waveguide are obtained. The space within the guide is NID in direction normal to walls of the waveguide. Field behaviour within the waveguide is noted for different values of the parameter, D, describing dimension of the NID space. For D = 2, classical results are recorded. The discussion is further extended by treating propagation in a tunnel within unbounded dielectric medium. The space within tunnel is also NID in direction perpendicular to walls of the tunnel. For different values of Dfield behaviors are also presented. It has been noted that for D = 2 and taking very high values of permittivity (ϵ → ∝) classical results for PEC waveguide are recorded. Whereas for ϵ → ∝, field behavior within tunnel matches with NID-PEC waveguide.

Two alternative approaches to the spatial spectral integral equation method are proposed. The first enhancement comprises a Hermite interpolation as the set of basis functions instead of the Gabor frame. The continuity, differentiability, equidistant spacing, and small support of these basis functions allows for an efficient and accurate numerical implementation. The second approach encompasses a method to transform between the spatial domain and the deformed path in the complexplane spectral domain. This method allows for more general path shapes, thereby removing the need to decompose the complex-plane spectral-domain path into distinct straight sections. Both enhancements are implemented for the case of TE polarization, and the results are validated against the finite element method and the rigorous coupled-wave analysis.

In this paper, to overcome signal-to-interference-and-noise ratio (SINR) performance degradation in the presence of steering vector (SV) mismatch between beam pointing and desired signal's SVs, we study the mismatch of SV with adaptive uncertainty level. This estimation is derived based on the geometrical interpretation of the mismatch and can be expressed as a simple closed-form expression as a function of the presumed SV and the signal-subspace projection. Then, the adaptive uncertainty algorithm self-adjusts the uncertainty sphere according to the estimated mismatch SV at each iteration. Finally, the robust adaptive sidelobe canceller (R-IASLC) algorithm can accurately evaluate the mismatches between the actual and presumed SVs and improve the target SINR. Simulation results verify the effectiveness of this method.

Semiconductor saturable absorber mirror (SESAM) based on InAs quantum dot (QD) material is important in designing fast mode-locked laser devices. A self-consistent time-domain travelling-wave (TDTW) model for the simulation of self-assembled QD-SESAM is developed. The 1-D TDTW model takes into consideration the time-varying QD optical susceptibility, refractive index variation resulting from the intersubband free-carrier absorption, homogeneous and inhomogeneous broadening. The carrier concentration rate equations are considered simultaneously with the travelling wave model. The model is used to analyze the characteristics of 1.3-μm p-i-n QD InAs-GaAs SESAM. The field distribution resulting from the TDTW equations, in both the SESAM absorbing region and the distributed Bragg reflectors, is obtained and used in finding the device characteristics including the modulation depth and recovery dynamics. These characteristics are studied considering the effects of QD surface density, inhomogeneous broadening, the number of QD absorbing layers, and the applied reverse voltage. The obtained results, based on the assumed device parameters, are in good agreement, qualitatively, with the experimental results.