Modeling complex networks of cables inside structures and modeling disjoint objects connected by cables inside large computational domains with respect to the wavelength are two problems that currently present many difficulties. In this paper, we propose a 1D/3D hybrid method in time domain to solve efficiently these two kinds of problems. The method, based upon finite difference schemes, couples Maxwell's equations to evaluate electromagnetic fields in 3D domains and the transmission line equations to evaluate currents and voltages on cables. Some examples are presented to show the interest of this approach.
Some new focusing properties of time-domain ultra wide band (UWB) focusing array antennas are presented. The large current radiator (LCR) is considered as the UWB antenna element. Each LCR is replaced by a set of infinitesimal dipoles modeling both the near field and the far field patterns of the antenna element and the coupling between the elements. Several antenna arrays with different sizes and number of elements are modeled. It is shown that similar to narrow band antennas, the actual maximum field region shifts from the intended focus region towards the antenna aperture.
Interference and multipath is one of the current issues in a wireless communication system, with complicated scenarios of environment especially in urban areas with a high number of users. Introducing smart antenna systems at the base station can contribute to reducing interference and improve quality of service. This paper proposes and explores the application of artificial immune system and negative selection algorithm to the prototype of smart antenna, where the proposed smart antenna is a hexagonal structure with 6-elements of the antenna array and working in LTE band at 2.6 GHz. Initial testing was done to define the RSSI value by calculating the average of the signal then comparing RSSI value defined by implementing artificial immune algorithm. To proof and determine actual RSSI signal received, a test in an anechoic chamber is conducted as reference that assumes free interference and multipath then compared to both of results. X-Bee module was used for transmitter and receiver in system at 2.4\,GHz band, and the proposed system prototype with hexagonal structure also used dual ARM microprocessor. Negative selection algorithm is applied in smart antenna programming to define actual values of receiving signal and angle of arrival. Every beam of the antenna were installed with an X-Bee module then connected to microprocessors, with an LED installed at each of the antenna as an indicator of beam switching or angle of arrival signal.
novel tapered slot antenna (TSA) with 3.5/5.5 GHz dual band-notched characteristics for ultra-wideband (UWB) radios is proposed in this paper. To realize dual band-notched characteristics at the TSA, we employ (a) a pair of nested C-shaped stubs beside the feed line and (b) a broadband microstrip-to-slot-line transition with an Archimedean spiral-shaped slot. The proposed antenna has been successfully simulated, implemented, and measured. An equivalent circuit model of the proposed antenna is also presented to discuss the mechanism of the dual band-notched TSA. The measured data for the optimized case show the bandwidth for the VSWR < 2 to be 9.2 GHz (from 2.4 to 11.6 GHz) with two notched bands of 3.1-4.0 GHz (WiMAX band) and 5.1-6.2 GHz (WLAN band), respectively. The measured electrical parameters of the proposed antenna and its radiation patterns show excellent performance with good pulse handling capabilities. Also, the 3.5/5.5 GHz dual band-notched characteristics are achieved without increasing the size of the single band-notched TSA reported previously.
In this paper, an octave bandwidth Doherty power amplifier (DPA) using a novel combiner is presented. The fundamental bandwidth limitation of the load modulation concept of a conventional Doherty structure is solved based on the proposed combination method. For verification, an octave bandwidth asymmetric Doherty architecture is implemented by using gallium-nitride (GaN) HEMT Cree CGH40010 and CGH40025 devices in the carrier and peaking amplifiers, respectively. The carrier and peaking amplifiers are designed to achieve optimal operation with 25 Ω load and source impedances. The reduced load and source impedances simplify the matching circuits for broadband operation. Key building blocks, including the proposed combiner, carrier and peaking amplifiers as well as the 50/25 Ω input power divider, are outlined. The measurement results represent higher than 37% and 52% drain efficiencies in 6 dB load modulation region across the frequency range from 0.85 to 1.85 GHz and 0.90 to 1.60 GHz, respectively. The implemented Doherty amplifier represents acceptable linearity across the whole operation frequency range. In two-tone signal characterization, the implemented DPA performs with a drain efficiency of 55% and an inter-modulation distortion (IMD) of -30 dBc at an average output power of 41.2 dBm at the center operation frequency of 1.35 GHz. In order to observe wideband signal characterization, a single carrier wideband code-division multiple access (W-CDMA) signal with a peak-to-average power ratio (PAPR) of 6.5 dB is applied and a drain efficiency of 51% with an adjacent-channel leakage ratio (ACLR) of -31 dBc is achieved at an average output power of 38.4 dBm.
This paper presents analytical formulas, based on the "thin wire model", for calculating the ELF (Extremely Low Frequency) sub-sea electromagnetic field produced by a submarine power cable. Two different models are studied: the first and simpler one (already present in literature) is based on the infinite sea model while the second and more realistic one, that we propose, takes into account of the seabed presence with the sea considered having finite depth. The shielding effect produced by cable sheath and armouring is taken into account by means of suitable shielding factors. Some examples of application of the two models are shown and the relevant results are compared between them.
Fractal antennas have undergone dramatic changes since they were first considered for wireless systems. Numerous advancements are developed both in the area of fractal shaped elements and fractal antenna array technology for fractal electrodynamics. This paper makes an attempt of applying the concept of fractal antenna array technology in the RF regime to optical antenna array technology in the optical regime using nonlinear array concepts. The paper further discusses on the enhancement of nonlinear array characteristics of fractal optical antenna arrays using nonlinearities in coupled antennas and arrays in a conceptual manner.
This paper presents the design and analysis of permanent magnet (PM) thrust bearing made up of three ring pairs for five degrees of freedom of the inner rings (rotor rings). The arrangement pattern of rings in PM bearing is considered in two ways: conventional structure and Halbach structure. The simplified three dimensional (3D) mathematical models employing Coulombian approach and vector method are used to design the bearing. MATLAB codes are written to evaluate the axial force, stiffness and moments in both the structures for five degrees of freedom, thereby the effect of axial, radial and angular displacements of the rotor on the aforementioned characteristics is addressed. The results of the mathematical model are validated by the results of 3D Finite Element Analysis (FEA) and experiments. It is observed that, the conventional structure seems to be more sensitive to the angular displacement, as the percentage decrease in force and stiffness is more with respect to angular displacement than the Halbach structure. The effect of angular displacement of the rotor on the performance of bearing in both the structures is crucial.
A Neural Network is a simplified mathematical model based on Biological Neural Network, which can be considered as an extension of conventional data processing technique. In this paper, an Artificial Neural Network (ANN) based simple approach is proposed as forward side for the design of a Circular Fractal Antenna (CFA) and analysis as reverse side of problem. Proposed antenna is simulated up to 2nd iteration using method of moment based IE3D software. Antenna is fabricated on Roger RT 5880 Duroid substrate (High frequency material) for validation of simulated, measured and ANN results. The main advantage of using ANN is that a properly trained neural network completely bypasses the complex iterative process for the design and analysis of this antenna. Results obtained by using artificial neural networks are in accordance with the simulated and measured results.
Imaging techniques based on time reversal method are particularly suitable for detection of targets embedded in a strongly scattering media. Generally in time reversal imaging technique we need to know the Green's function of the medium and the exact locations of the transmitter and receiver antennas. We introduce a target imaging method in which imaging is made with an arbitrary placement of the transmitting or receiving antennas. Numerical simulations are used to illustrate the capabilities of the proposed algorithms in different scenarios. We use the two-dimensional finite difference time domain method in our simulations. The numerical simulations are done for a typical through-the-wall scenario. We also present results in which the same method is used for tracking targets behind the wall.
A self calibration algorithm for direction finding in the presence of arbitrary shape 3D scatterers of resonating size is presented. This algorithm removes the effects of mutual coupling and 3D scatterers on direction of arrival estimation. The scatterers and wire type antenna array are excited by incident plane waves of arbitrary direction. The 3D scatterers shape is approximated as a sphere, thus spherical harmonics are assumed to be originated in response to the plane wave excitation. The algorithm requires the location of the scatterers with reference to antenna elements. However, knowledge of exact shape of scatterers is not required. Moreover, scatterers may be located in near or far fields. The work is supported by numerical examples for different scenarios of multiple incident waves and scatterers.
The aim of this work is to implement a hybrid approach able to provide an efficient solution of the electromagnetic coupling between an antenna and an obstacle distant few meters away. The idea is to divide the problem into a small number of less complex sub-problems exploiting the advantage of generating the admittance matrix that describes the scattering problem by a numerical code. To this end, the electromagnetic field impinging on the object has been characterized by means of a proper number of very narrow beams; for each beam the scattering problem has been solved by a commercial code; finally, the total admittance matrix has been obtained as composition of all the scattering contributions. The resulting echoof a moving obstacle has been compared with that measured by experimental investigations, both for metallic and dielectric bodies.
UWB antenna is a crucial part of any UWB system required for indoor application. In this paper a novel design is presented, which relies on self-complementary structure. The structure is fed by a microstrip line, where a triangular notch is embedded in the ground plane. The design in this paper yields a UWB bandwidth that extends from 2.86.0-40.0 GHz. To ensure coexistence of UWB with WLAN applications (5.15-5.825 GHz) with minimal interference, a frequency notch is introduced using two parasitic U-shaped elements embracing the microstrip feeding line that resonates in the vicinity of the band notch frequency band. The proposed design was subject to parametric study to reach optimum parameters. The final design was fabricated using photolithographic technique and the measured results showed very good agreement with simulated ones.
This paper proposes an investigation in the terahertz (THz) frequency range of the dispersion and an individual quantitative treatment of the losses of the most classical microwave waveguides (coplanar, slotline, microstrip and stripline) numerically led in three dimensions (3D). An original strategy has been used to quantify radiation losses associated with leaky modes. A very low THz permittivity polymer (benzocyclobutene (BCB)) was used as a very convenient substrate to be easily grafted as a THz environment of integrated passive or/and active devices. Direct comparisons of the losses and the dispersion have been performed following two criteria: a constant characteristic impedance Z_{c} fixed at 100 Ω and a constant effective width Weff fixed at 30 μm. The best waveguides are microstrip (α_{T}= 2.52 dB/mm for Z_{c}= 100 Ω and for W/H=35/50 μm (with W the strip width and H the substrate height) and α_{T} =2.29 dB/mm for W_{eff} = 30 μm at 1 THz with H = 30 μm) and stripline (with quasi-null radiation losses and the best quality factor Q_{T}= 63 for Z_{c} = 100 Ω). The large dispersion and radiation losses of the slotline (SL) can be reduced with a thick BCB encapsulation to enhance the THz signal. The coplanar waveguide (CPW) remains in a medium position. Besides the parasitic mode (SL) and low Q_{T} problems due to mainly ohmic losses, its major advantage is its planar geometry allowing to an easy circuit integration with THz sources, amplifiers and detectors based on semiconductor. Consequently, these THz studies on BCB microwave standard waveguides open to various perspectives to carry out a broad panel of integrated THz circuits.
Two multi-band filters operating in the 1-10 GHz range are designed, analytically studied and experimentally verified. The filters are developed by making modifications to a series capacitively coupled, microstrip line filter. The middle section of the microstrip line is widened and rectangular slots are etched on it. Widening increases the effective dielectric constant which helps in miniaturization of the circuit. On the other hand, the rectangular slot cause various longitudinal, transverse and slot mode resonances to be excited resulting in multi-band operation. An extensive parametric analysis with respect to the physical parameters of the filter leading to the development of a semi-empirical model is presented. The model can be used to predict the resonant frequencies with sufficient accuracy for a given geometrical structure. The model also predicts the limit of miniaturization achievable with the presented design. The proposed filters besides being compact have good out of band rejection and are easy to design and fabricate without the need of additional matching circuits.
Results of a self-consistent computational analysis based on a mathematical model of resonance scattering and generation of waves on an isotropic nonmagnetic nonlinear layered dielectric structure excited by a packet of plane waves are presented, where the analysis is performed in the domain of resonance frequencies. Physically interesting properties of the nonlinear permittivities of the layers as well as their scattering and generation characteristics are obtained, for instance the characteristic dynamical behaviour of the relative Q-factor of the eigenmodes and the energy of higher harmonics generated by canalising as well as decanalising nonlinear layers. The results demonstrate the possibility to control the scattering and generating properties of a nonlinear structure by means of the excitation intensities.
This paper describes an experimental model for the characterization of electromagnetic phenomena that occur in the end regions of large turbo-generators. The study is based on a test bench that contains a stack of steel laminations from a 900 MW turbogenerator stator and two exciting circuits in order to combine a transverse magnetic flux with the in-plane flux. In order to explain the flux penetration within the magnetic sheet stack, accurate experimental measurements are performed. Results are compared with the finite element simulations using code_Carmel3D. In the same time, theoretical and experimental results are analyzed with a view to examining the influence of transverse flux on additional losses.
There has been a surge of interest in the subwavelength confinement effects of the electromagnetic fields. Based on these effects, one can obtain new behaviors of the near- and farfield radiation. It is well known that in optics, the subwavelength confinement can be obtained due to surface-plasmon (or electrostatic) oscillations in metal structures. This paper is a review of recent studies on the subwavelength confinement in microwaves due to magnetic-dipolarmode (MDM) [or magnetostatic (MS)] oscillations in small ferrite samples. MDM oscillations in a mesoscopic ferrite-disk particle are quantized oscillations, which are characterized by energy eigenstates. The field structures are distinguished by power-flow vortices and non-zero helicity. Also in vacuum, the near fields originated from MDM particles are designated by topologically distinctive power-flow vortices, non-zero helicity, and a torsion degree of freedom. To differentiate such field structures from regular electromagnetic (EM) field structures, we term them as magnetoelectric (ME) fields. In a pattern of the microwave field scattered by a MDM ferrite disk and MDM-disk arrays, one can observe rotating topological-phase dislocations. This opens a perspective for creation of engineered electromagnetic fields with unique symmetry properties. In the near-field applications, we propose novel microwave sensors for material characterization, biology, and nanotechnology. Strong energy concentration and unique topological structures of the near fields originated from the MDM resonators allow effective measuring chiral properties of materials in microwaves. Generating far-field orbital angular momenta from near-field microwave chirality of MDM structures can be a subject of a great interest. Realization of such vortex generators opens perspective for novel microwave systems with topological-phase modulation.
The analysis and design of the multi-element coupled lines, in conjunction with the junction discontinuity effect, is presented, and its applicability in high power rf regime is discussed. Junctions are usually employed to connect two different coupled elements, which gives rise to undesirable reactance i.e. junction discontinuity effect. These effects are found prominent in the high power coupled lines for HF and VHF applications because of its large structural dimensions. The design and simulation of 3-element, 8.34±0.2 dB coupled line section rated for 38 to 112 MHz and 200 kW has been performed. The simulated results are significantly deviated from the theoretically calculated ones where the discontinuity effect is usually ignored. A generalized theoretical procedure is developed to take into account the effect of junction discontinuity at the designing stage. The theory is applied to the 3-element 8.34±0.2 dB coupled-line section, and simulation is performed by using standard Ansoft HFSS software. The HFSS simulation results are in close agreement with the theoretical predictions.
Microwave pyrolysis overcomes the disadvantages of conventional pyrolysis methods by efficiently improving the quality of final pyrolysis products. Biochar, one of the end products of this process is considered an efficient vector for sequestering carbon to offset atmospheric carbon dioxide. The dielectric properties of the doping agents (i.e., char and graphite) were assessed over the range of 25°-400°C and used to develop a finite element model (FEM). This model served to couple electromagnetic heating, combustion, and heat and mass transfer phenomena and evaluated the advantages of selective heating of woody biomass during microwave pyrolysis. The dielectric properties of the doping agents were a function of temperature and decreased up to 100°C and thereafter remained constant. Regression analysis indicated that char would be a better doping substance than graphite. The simulation study found that doping helped to provide a more efficient heat transfer within the biomass compared to non-doped samples. Char doping yielded better heat transfer compared to graphite doping, as it resulted in optimal temperatures for maximization of biochar production. The model was then validated through experimental trials in a custom-built microwave pyrolysis unit which confirmed that char doping would be better suited for maximization of biochar.