In this paper, a beam switchable antenna solution for vehicular use is presented. Main objective is to improve the cellular connectivity of vehicles operating in poor coverage region. An adaptive antenna system operating in the frequency band 824-960 MHz having high gain, and full azimuth plane coverage, and main beam in elevation plane pointing towards 90˚, was developed. Beam switchable antenna provides beam-steering in azimuth plane, by switching one antenna element active at a time. The concept of stacked patch antenna with L probe feed was used for a single element. This arrangement gives gain of 7.4-8.2 dBi, and total radiation eciency of 0.11 dB, over the band, with broadside radiation pattern, and half power beam width of single element up to 80˚. The field measurements for the designed antenna system were performed in poor coverage regions using commercial cellular network. Results were compared to corresponding results of conventional vehicular antenna, having omnidirectional radiation pattern and the gain of 3 dBi. The developed antenna system results in 3.5...12.7 dB higher RX level than reference antenna and increase communication range from 71 km to 109 km in open area. Similarly, in suburban area the communication range is increased from 20 km to 30.8 km. Also, the narrower beam acts as spatial filter and results in reduced fading.
A new single-layer element structure for broadband operation is presented. The element is composed of a circular ring attached two sets of phase-delay lines with the opposite direction of rotation. The demission of circular ring is fixed, and about 460° reflection phase range is achieved by varying the length of the phase-delay lines. Using the proposed element, a 381-element single-layer linearly polarized reflectarray is designed, fabricated and measured. A gain of 27.5 dB is measured at 13.58 GHz with 3-dB beamwidth of about 6.8°, and the corresponding aperture efficiency is 57.3%. Good radiation performances are also achieved at other frequencies. Measured results show 1.5-dB and 3-dB gain bandwidth of 47.8% (13.58-20.08 GHz) and 64% (12.08-20.78 GHz) with the center frequency of 13.58 GHz respectively, which demonstrates excellent broadband performance. Besides, high aperture efficiencies (more than 50%) are achieved in a wide frequency range (12.08-17.08 GHz). Low cross polarization and sidelobe levels are also achieved in the frequency band.
A process is introduced to design and validate insertable rectangular-waveguide verification standards for the electromagnetic characterization of materials using the Nicolson-Ross-Weir method. Each insertable structure consists of a series of metal steps that acts as a surrogate material exhibiting smooth and predictable permittivity and permeability characteristics across the waveguide band. These known material properties can be used to assess the performance of material characterization systems. Since the verification standards are inserted into the waveguide in the same manner as samples under test, each step in the normal measurement procedure is duplicated. A specific example of an S-band verification standard is presented, with the standard fabricated using two different methods. The first standard is machined from a solid metal block while the second is constructed by metalizing a 3-D printed polymer structure. Comparison of the predicted material parameters to those extracted from experimental data demonstrates the utility of the proposed insertable standards.
A new direction finding method for multiple-input multiple-output (MIMO) radar with non-circular sources is proposed. The method takes advantage of the properties of non-circular sources to formulate a new virtual array. Then based on the ESPRIT like algorithm, the bearing of targets is estimated. In addition, the direction of departure (DOD) and direction of arrival (DOA) are paired automatically. Compared with the uniform circular array estimation of signal parameters by rotational invariance techniques (UCA-ESPRIT), the proposed method achieves better estimation performance and can deal with more sources. We also provide the Cramer-Rao Lower Bound (CRLB) for comparison. Simulation results demonstrate the effectiveness and feasibility of the proposed method.
In this work, a new technique in suppressing the effect of four-wave mixing (FWM) by Odd-Even Channels Arrangement (OEC) is presented. The proposed technique is verified mathematically and by simulations with other recent techniques which are input power and channel spacing under the same input parameters. Simulation was done with the power variation effect, and the bit rate was 100 Gb\s. Based on theoretical and simulation analyses, FWM power was drastically reduced by more than 10 dB when OEC was conducted. In terms of system performance, OEC offered better performance than previous techniques in both theoretical and simulation analyses.
Sparse regularization imaging method (SRIM) is an effective approach to implement azimuth super-resolution for forward-looking scanning radar. However, for the scene that contains adjacent strong targets in the continuous weak background, SRIM may destroy the structure of the scene when trying to separate the closely located targets. In this paper, a divide and conquer regularization imaging method (DC-RIM) is proposed to solve this problem. Firstly, the data are divided into two channels by the mean-variance segmentation method. Normally, we consider that the data of channel I contain strong scatterers and that the data of channel II contain weak background. Afterwards, SRIM is conducted on channel I to distinguish the targets. For the data of channel II, a region enhancement regularization method is particularly proposed to acquire a good structure of the scene by making use of two-order gradient information of the data. Finally, a good imaging result can be obtained by combining the results of two channels. Experiments based on both synthetic and real data are given to verify the effectiveness of the method.
This paper describes an experimental study of passive intermodulation due to metal-tometal contacts with focus on shape influence. This study investigates PIM value of different contact geometric profiles and different contact areas versus normal forces. A complete description of profiles used is done to achieve a relationship between PIM level and contact shape.
This paper discusses the torque constant density in different types of Double Stator Permanent Magnet Brushless DC Motor (DSPM) which are designed for portable applications. It should have high torque constant density so that it will have higher torque as well as lightweight. Previously, there have been many DSPM motor designs that only focus on increasing the torque constant and torque density. However, it is unclear which DSPM motor is the best since the torque constant and torque density are different parameters. Torque constant density will include the torque, volume and current of the motor. The objective of this research is to analyze different types of DSPM motors including the proposed Slotted Rotor DSPM motor (DSPM-SR) which produces higher torque constant density. Besides that, this paper also describes in detail the torque constant density from an electromagnetic point of view. Finite Element Analysis (FEA) and analytical calculation are used to simulate the characteristic of various double stators. The result shows that DSPM-SR has 90.5% higher back electromotive force (emf) and 87.5% higher torque than DSPM-ST. Besides that, the DSPM-SR topology has higher torque constant density about 67.27% than other DSPM motors. As a conclusion, this paper provides the overview and comparison of torque constant densities of various DSPM motors.
A two-dimensional Green's function for a half space geometry, comprising planar interface only due to two different non-integer dimensional spaces, has been derived. Medium hosting the time harmonic electric line source and planar interface is homogeneous and isotropic. Radiated field is written in terms of unknown spectrum of plane waves. Unknown spectrum functions are determined using the related boundary conditions. It has been shown that although wavenumbers of both half spaces are same, due to difference of dimensions of the two half spaces, reflection and transmission occur. When dimensions of both half spaces are taken equal to two, derived expressions yield field radiated by a line source in an unbounded homogeneous medium with integer dimensional space.
A symplectic pseudospectral time-domain (SPSTD) scheme is developed to solve Schrodinger equation. Instead of spatial finite differences in conventional finite-difference time-domain (FDTD) methods, fast Fourier transform is used to calculate spatial derivatives. In time domain, the scheme adopts high-order symplectic integrators to simulate time evolution of Schrodinger equation. A detailed numerical study on the eigenvalue problems of 1D quantum well and 3D harmonic oscillator is carried out. The simulation results strongly confirm the advantages of the SPSTD scheme over the traditional PSTD method and FDTD approach. Furthermore, by comparing to the traditional PSTD method and the non-symplectic Runge-Kutta (RK) method, the explicit SPSTD scheme, which is an infinite order of accuracy in space domain and energy-conserving in time domain, is well suited for a long-term simulation.
A variety of techniques are available to reduce cogging torque in Permanent Magnet Brushless DC (PMBLDC) motors. In general, all the techniques are meant for effectively reducing the cogging torque. This paper presents a new technique for cogging torque reduction in a radial flux surface mounted PMBLDC motor by applying the proposed T-shaped bifurcation method in the stator teeth of a PMBLDC motor. The Finite Element Analysis (FEA) is carried out for the T-shaped bifurcation method applied to a PMBLDC motor, and analysis is done using Virtual Work (VW) method. The CAD software package MagNet has been used to completely analyze the T-shaped bifurcation based PMBLDC motor. FEA and CAD simulated results are compared for the reduction of cogging torque values. It is found that the cogging torque reductions in the two methods are nearly the same. The cogging torque and the flux density values of the motor calculated using the proposed T-shaped bifurcation method are compared with the corresponding values of the recently introduced Reduced Stator Slot Width method. The proposed T-shaped bifurcation is very effective compared to the existing techniques in reducing the cogging torque.
A new optimization algorithm for the Cylindrical Polarimetric Phased Array Radar (CPPAR) antenna pattern synthesis is presented to achieve multi-mission requirements. To allow accurate weather measurements, the CPPAR antenna needs to have matched co-polarization (H and V) patterns, low sidelobe levels and high cross-polarization purity. To achieve these goals, first, a high-performance dual-polarized hybrid-fed microstrip patch antenna is designed, and its embedded radiation pattern is extracted. Then, a pattern synthesis using a new optimization method is presented to find the optimal weights for each radiating element and each polarization. The modified particle swarm optimization (MPSO) with new features is used to optimize the current distribution of the CPPAR. The adaptive beamforming algorithm also has the capability to mitigate interference by steering nulls of the radiation pattern in the desired direction without aecting the main beam. The performance improvement is demonstrated through the simulation results.
This paper presents a direction of arrival (DOA) estimation method. Spectral-domain interferometer equation is first established based on integral transforms of spatial interferometer equations. The direction finding problem in the spatial domain is thereby mapped to that in the spectral domain, relating angular parameters to spatial spectrums. This method is then applied to DOA estimation with circular arrays and spherical arrays. As a result, the elevation angle and azimuth angle are decoupled, giving closed-form and analytical formulae for DOA estimations by discrete phase samples on a sampling aperture. Algebraic relations between angular parameters and phase samples are established, and this method is hence computationally efficient. The Cramer-Rao lower bound (CRLB) of the proposed method is derived, and accuracy analysis demonstrates that the proposed method approaches the CRLB. In addition, mathematical insights into accuracy enhancement by large number of samples are observed via Parseval's theorem. Finally, numerical simulations and experimental measurements are provided to verify the effectiveness and appealing performance of the proposed method.
This paper presents the performance of cylindrical plasma antenna. A plasma tube is used as radiating element. The antenna is designed and works at different frequencies. To couple electromagnetic signal from the coaxial probe to the plasma column, a coupling system is realized. It permits to excite the tube in order to have a monopole or dipole antenna. The performances of the cylindrical plasma antenna are given in terms of S11, gain and radiations patterns.
A miniaturized serpentine patch antenna is presented for Industrial, Scientific and Medical band (2.4-2.48GHz) applications. The proposed antenna is fabricated on a Rogers RT/duroid5880 substrate having permittivity of 2.2 and loss tangent of 0.0009. In comparison with other traditional structures, this antenna has an electrical length of 0.961λ with 29.2% impedance bandwidth which is advantageous for higher data rate transmission. In order to test the performance, the proposed antenna is tested in a silicone feeding tube. The simulated and measured results show good agreement with each other. Defected ground structure is also incorporated to enhance the performance of the proposed structure. All the simulations have been carried out on FDTD based Empire XCcel tool.
The basic wave types of electromagnetic field propagation in anisotropic media are obtained. Based on the orthogonality relation between the vector wave functions and the orthogonality of trigonometric functions, etc., the expressions of zero order scattering fields and first-order scattered fields of arbitrary electromagnetic beam are presented. A stochastic system identification model for electromagnetic beam scattering by anisotropic particles is established. In the S wave band, the relationships respectively between the scattering field expansion coefficients, the basic wave types of the particle field and the tensor of dielectric constant are studied, and their validity of the model is verified. Taking the elliptical Gaussian beam as an example, the beam scattering characteristics of anisotropic media particles are investigated. The used method is simple, exploring a new approach of researching the electromagnetic beam scattering characteristics from anisotropic medium targets.
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.
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 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.