Random antenna array (RAA) that uses the conventional beamforming method produces a poor beam pattern with high sidelobe level. This greatly reduces the performance and the efficiency of the antenna. The use of Genetic Algorithm (GA) to find the best positions for the antenna elements in RAA to lower the sidelobes has been widely researched. However, there has been no solution proposed for the reduction of sidelobes when the user has no autonomy over the position of the radiating elements, for instance in cases such as emergency communications. This paper proposes a novel Pareto Elite Selection Genetic Algorithm (PESGA) optimization method to reduce the sidelobes in an RAA that has fixed elements' position. The proposed method uses a single fitness function (peak sidelobe level) for parent selection while an additional function (number of sidelobes above a threshold level) is introduced to select the elitist in every generation via Pareto Front (PF) selection. Results indicate that the proposed PESGA method is best used for scenarios where the array size is small. In such cases, the proposed method provides much reduced sidelobe compared to the conventional RAA beamforming method and up to 200% improvements in terms of mainlobe to peak sidelobe ratio compared to GA weight optimized beamforming method.
In this paper we present a methodology to guarantee the convergence of the electromagnetic inverse method. This method is applied to electromagnetic compatibility (EMC) in order to overcome the difficulties of measuring the radiated electromagnetic field and to reduce the cost of the EMC analysis. It consists in using Genetic Algorithms (GA) to identify a model that will be used to estimate the electric and magnetic field radiated by the device under test. This method is based on the recognition of the equivalent radiation sources using the Near Field (NF) cartography radiated by the device. Our contribution in this field is to improve the ability and the convergence of the electromagnetic inverse method by using the Pseudo Zernike Moment Invariant (PZMI) descriptor and the Artificial Neural Network (ANN). The validation of the proposed method is performed using the NF emitted by known electric and magnetic dipoles. Our results have proved that the proposed method guarantees the convergence of the electromagnetic inverse method and that the convergence speeds up while retaining all the other performances.
Focusing of electromagnetic plane wave from a large paraboloidal reflector, composed of layers of chiral and/or chiral nihility metamaterials, has been studied using Maslov's method. As a first step, the transmission and reflection of electromagnetic plane wave from two parallel layers of chiral and/or chiral nihility metamaterials are investigated using transfer matrix method. The effects of change of angle of incidence, chirality parameters and impedances of layers are noted and discussed. Special cases by taking extreme values of permittivity of second layer, while assuming value of corresponding chirality equal to zero, are also obtained for validating the methodology. These special cases are equivalent to reflection from a perfect electric conductor backed chiral layer and nihility backed chiral layer, respectively. Results of reflection from parallel layers have been utilized to study focusing from a large paraboloidal reflector. The present study, on focusing from a paraboloidal reflector, not only unifies already published work by various researchers but also provides better understanding of the problem.
A new miniaturized ultra-wideband bandpass filter with embedded reconfigurable multiband frequency notch function was designed and implemented by embedding all the passive components into a printed circuit board with a high dielectric constant. The proposed filter consists of compact 2U-shaped DGS resonators shunt connected to parallel coupled lines to achieved frequency notch. To tune the notched band, suitable capacitor elements within the inner/outer U-DGS and RF PIN diode within the outer U-DGS are integrated. A curve fitting formula is derived to show the effect of the capacitor value on the center frequency of the notched band, which is decreased by 56.7%. These capacitors improved the quality factor and have the effect of reducing the filter size by 72% as compared to other filters. The RF PIN diode in the outer U-DGS acts as a switch to exhibit a band notch covering the bandwidth of the WLAN for IEEE 802.11 a/h at 5.5 GHz and RFID ISO 18000 series pars5 in microwave (MW) which is set at 5.8 GHz, 6.1 GHz and 6.8 GHz, and the other bands. RF PIN diodes control the notched band and raises it from 5.25 GHz to 6.85 GHz (27%) or remove the band notched according to its positions. In order to validate the feasibility of the proposed structure, UWB BPF with center frequency of 6.85 GHz is designed, fabricated, and measured. The filter has passband from 3.2 GHz to 10.7 GHz and notched band designed to generate stop band from 5.25 to 6.85 GHz, and the two transmission zeros are observable at 2 GHz and 12.5 GHz, respectively by measurement. This paper shows the miniaturized filter with size 6.7 mm x 65 mm occupying a circuit area of about 0.41λg by 0.39λg. The measured results for the proposed filter are in good agreement with simulations and verifies the excellent performance of the designed filter and the validity of the proposed approach.
The wireless communications in a tree canopy is essential for pre-harvesting control of fruit productions. To efficiently communicate between a sensor node and a sink node, channel characteristics in a tree canopy must be well-established. In this paper, propagation channel characteristics at the frequencies of 2.45 and 5.2 GHz have been estimated for designing a wireless communication system in a tree canopy. The proposed solution is based on measured path loss, time-varying signal strength and Angle of Arrival (AoA) for various paths in a tree canopy to estimate the channel. Since the waves reflect, refract, diffract and scatter from the foliage, it is complicated to find the true travelling path between a transmitter and a receiver at the nodes. The AoA estimator is used for physical interpretation of the channel. The experimental results demonstrate the channels in a tree canopy are mostly matched with the General Extreme Value model. The measured path gains illustrate that the appropriate antenna patterns must be selected to enhance the reliability of the system.
A free-space, non-destructive method for measuring the complex permittivity of a double-layer bulk dielectrics and thin film oxide layers at microwave frequencies have been developed. The method utilizes a spot-focusing antenna system in conjunction with a vector network analyzer in the range of 18-26 GHz. The bulk dielectric was measured using the Transmission Method and Metal-Backed Method, while the Metal-Backed Method was used to investigate the thin films. Both types of samples were sandwiched between two quarter-wavelength Teflon plates to improve the mismatch at the frequencies of measurement. The thin film sample arrangement was backed by an additional metal plate. The double-layer bulk dielectric samples were Teflon-PVC and Plexiglas-PVC, while the thin film samples consisted of SiO2 layers of different thicknesses grown on doped and undoped Si wafer substrates. The relative permittivity obtained for PVC ranged between 2.62 to 2.93, while those for Plexiglas exhibited values between 2.45 to 2.63. The relative permittivity of SiO2 deposited on these wafers was between 3.5 to 4.5. All these values were in good agreement with published data The advantage of the method was its ability to measure the dielectric properties of the films at the mid-frequency band irrespective of the substrate type used. Simulations of the measurement setup were carried out using CST Microwave Studio and the simulation results agreed closely with the measurements.
An analysis method for electromagnetic field coupling to microstrip line connected with nonlinear components is proposed in this paper. Different from the published work, not only the voltage and current response of the nonlinear component connected to the transmission line (TL) can be obtained, but also the power transmitted from this nonlinear component to the next one at both the fundamental frequency and harmonics can be predicted. The proposed method suitably combines the classical field-to-TL coupling theory and the nonlinear large-signal scattering parameters on the basis of a black box model in frequency-domain. Then this method is experimentally validated by a laboratory system including a microstrip line connected with a simple nonlinear component constituted by the anti-paralleled HSMS-282C Schottky diodes pair welded to a 50 Ω microstrip line. The calculated results using the proposed method show good agreement with the measured data.
It has been known through some examples that parameters of an electromagnetic medium can be so dened that there is no dispersion equation (Fresnel equation) to restrict the choice of the wave vector of a plane wave in such a medium, i.e., that the dispersion equation is satised identically for any wave vector. In the present paper, a more systematic study to define classes of media with no dispersion equation is attempted. In addition to the previously known examples, a novel class of Case 1 media with no dispersion equation is seen to emerge through the analysis making use of coordinate-free four-dimensional formalism in terms of multivectors, multiforms and dyadics.
D′B′, DB′ and D′B boundary conditions are used to investigate the resulting field patterns inside a parallel plate waveguide. The D′B′ boundary conditions are accomodated by assigning the behavior of perfect magnetic conductor (PMC) for transverse electric mode (TE) and that of perfect electric conductor (PEC) for transverse magnetic (TM) mode, to the boundary, respectively. Likewise, DB′ boundary conditions are incorporated by assuming the behavior of boundary as PMC for both the TE mode and TM mode. Finally D′B boundary conditions are realized by assigning PEC characteristic to the boundary for both TE and TM modes. A general wave propagating inside the parallel plate waveguide is assumed and decomposed into TE and TM modes for the purpose of analysis. Fractional curl operator has been used to study the fractional parallel plate D′B′, DB′ and D′B waveguides for different values of fractional parameter α. Behavior of the field patterns in the waveguides are studied with respect to the fractional parameter α describing the order of the fractionalization.
We study the current distribution and input impedance of a circular loop antenna in the form of an infinitesimally thin, perfectly conducting narrow strip coiled into a ring. The antenna is located on the surface of an axially magnetized plasma column surrounded by a homogeneous isotropic medium. The current in the antenna is excited by a time-harmonic voltage creating an electric field with the azimuthal component in a gap of small angular opening on the strip surface. The emphasis is placed on the solution of the integral equations for the azimuthal harmonics of the antenna current in the case where the magnetoplasma inside the column is nonresonant. The properties of the kernels of the integral equations are discussed and the current distribution in the antenna is obtained. It is shown that the presence of a magnetized plasma column can significantly influence the electrodynamic characteristics of the antenna compared with the case where it is located in the surrounding medium or a homogeneous plasma medium the parameters of which coincide with those inside the column.
Eggs are one of the most nutritious foods available in nature. This rich nutritive environment attracts microbes to invade, feed and multiply. Salmonella enteritidis is one such microbe that is highly pathogenic and is the causative agent for the disease salmonellosis. To ensure safety of eggs, processing them without affecting their unique physical properties is essential. In this study, the impact of radiofrequency (RF) heating on the dielectric properties (dielectric constant and dielectric loss factor) of the egg at varying temperatures (5°C-56°C) and frequency (10 MHz-3 GHz) is evaluated. This study on the dielectric parameters is essential to devise a better heating paradigm wherein there is minimal detrimental effect to the egg components. Based on the dielectric study, the heating process parameters were determined. The effect of such heat treatment on the physical properties viz. Viscosity, foam density, foam stability and turbidity of the egg white were also studied. This study was conducted to provide sufficient literature and experimental background for employing RF in pasteurization of in-shell eggs. This study showed that if careful process parameter optimization and meticulous equipment design is done, RF heating can be successfully employed to pasteurize in-shell eggs.
Three hexagonal patch antennas are designed for circular polarization and experimentally validated. These antennas are labeled; simple hexagonal patch, hexagonal patch with slotted ground and hexagonal patch with parasitic element. The measured impedance bandwidths of the three antennas are 2% for the simple patch, 5.2% for the patch with slotted ground and 6.35% for the antenna with parasitic element. The axial ratio (measured) obtained is 4.73% for the patch with slotted ground and 3.33% for the hexagonal patch antenna with parasitic element. The measured radiation patterns of these antennas are found to be in good agreement with the simulated radiation patterns. The average gain of all the three antennas is also evaluated. A frequency selective surface (FSS) is proposed with dimensions smaller than that of a conventional FSS structure. The measured gain improvement with the proposed FSS is around 3 dB in the operating band.
In this paper we present designs of fibersμ having non-zero positive, non-zero negative and near-zero ultra-flattened dispersion with small dispersion slope and ultra-large effective area over a wide spectral range. The designs consist of a concentric multilayer segmented core followed by a trench assisted cladding and a thin secondary core. The central segmented core helps in maintaining desired dispersion over a wide range of wavelength. The second core of the fiber helps in achieving ultra-large effective area and trench assisted cladding reduces the bending loss. The designs of the fiber have been analyzed by using the transfer matrix method. For positive non-zero dispersion flattened fiber we have optimized dispersion near +4.5 ps/km/nm in the wavelength range 1.46-1.65 μm. Maximum value of dispersion slope of the fiber in above mentioned wavelength range is 0.026 ps/km/nm2. In the design of negative non-zero dispersion flattened fiber, dispersion has been achieved near -6 ps/km/nm in the spectral range of 1.33-1.56 μm and maximum value of dispersion slope is 0.048 ps/km/nm2. Dispersion and dispersion slope of near zero dispersion flattened fiber lie in the range [0.0039-0.520] ps/km/nm and [(0.0004)-(0.0365)] ps/km/nm2 respectively in the spectral range of 1.460-1.625 μm. The near zero dispersion flattened fiber has an ultra-high effective area ranging from 114 μm2 to 325.95 μm2 in the aforementioned wavelength range, which covers the entire S+C+L-band. These values of mode area are noticeably higher than those reported in literature for flattened dispersion fibers with large mode area. Designed fiber show very small bending loss. We report breakthrough in the mode area of the single mode optical fiber with ultra flattened dispersion and low dispersion slope.
In this paper, a new numerical method of calculating rectangular busbar impedance is proposed. This method is based on integral equation method and partial inductance theory. In particular, impedances of shielded and unshielded three-phase systems with rectangular phase and neutral busbars, conductive enclosure, and use of the method are described. Results for resistances and reactances for these systems of multiple rectangular conductors have been obtained, and skin and proximity effects have also been taken into consideration. The impact of the enclosure on impedances is also presented. Finally, two applications to three-phase shielded and unshielded systems busbars are described. The validation of the proposed method is carried out through FEM and laboratory measurements, and a reasonable level of accuracy is demonstrated.
Simulations based on electromagnetic topology (EMT) have been carried out to analyze an external electromagnetic pulse interaction with a shielded coaxial cable linking two systems together. The proposed EMT approach, combined with the SPICE model of the shielded cable, can be applied in the transient simulation directly and used for the electromagnetic interference analysis of systems including nonlinear devices. The effects of the outer terminators, cable length, and connection of the voltage limiter on the induced voltages at the systems are studied by using the proposed EMT approach. It has been found that adding a resistance between the system's shielding enclosure and the ground can effectively reduce the coupling through the shielded cable. The cable length affects the pulse-widths rather than the magnitudes of the induced voltages. The results also show that the voltage limiter can reduce the induced voltages but at the same time result in mismatch at the source or load.
In this paper, a new technique is proposed to optimize the conflicting parameters like low value of maximum side lobe level (SLL), narrow beam-width of the main beam and low value of maximum sideband radiation level (SRL) of time-modulated linear antenna arrays (TMLAAs). The method is based on minimizing a multi-objective fitness function by using single-objective differential evolution algorithm (DEA) technique. The method is applied to both uniformly excited TMLAA (UE-TMLAA) and non-uniformly excited TMLAA (NUE-TMLAA) to synthesize low side lobe optimum pattern at operating frequency by suppressing the sideband radiation level to a sufficiently low value. For UE-TMLAA only the switch-on time durations of the array elements and for NUE-TMLAA the switch-on time durations and the static amplitudes with predetermined dynamic range ratio (DRR) of static amplitudes are taken as the optimization parameters for the DEA. To show effectiveness of the proposed approach, the single-objective DEA optimized results are compared with those obtained by other single objective and multi-objective techniques that has been reported previously. Also, first null beam width (FNBW) and half power beam width (HPBW) of the DEA optimized patterns at fundamental radiation are compared with those of the Dolph-Chebyshev (D-C) pattern of same SLL.
The practically important case of a dielectric-loaded tape helix enclosed in a coaxial perfectly conducting cylindrical shell is analysed in this paper. The dielectric-loaded tape helix for guided electromagnetic wave propagation considered here has infinitesimal tape thickness and infinite tape- material conductivity. The homogeneous boundary value problem is solved taking into account the exact boundary conditions similar to the case of anisotropically conducting open tape helix model [1,2]. The boundary value problem is solved to yield the dispersion equation which takes the form of the solvability condition for an infinite system of linear homogeneous algebraic equations viz., the determinant of the infinite-order coefficient matrix is zero. For the numerical computation of the approximate dispersion characteristic, all the entries of the symmetrically truncated version of the coefficient matrix are estimated by summing an adequate number of the rapidly converging series for them. The tape-current distribution is estimated from the null-space vector of the truncated coefficient matrix corresponding to a specified root of the dispersion equation.
With the renewed application of millimeter technology in remote sensing, radio astronomy, and meteorological satellite, millimeter wave antennas of electrically large aperture are frequently deployed. Shaping techniques are accordingly developed to meet different requirements. In this paper, a shaping technique for the scanning reflector antenna system of a remote sensing spacecraft is presented. The shaping technique is based on Fourier optical theory to control the maximal radiating direction of the antenna system. To implement such functionality, a new shaping technique of the sub-reflector has been developed. In addition, rotation of the shaped sub-reflector can achieve scanning purpose with identical footprints in all scanning angles. Case studies have been performed to verify the shaping technique.
A new type of cascaded series feed beamforming networks (BFNs) is introduced. The network architecture is based on a dual-series Nolen matrix topology. It is able to produce tapered output amplitude distributions from NxN configurations. The general concept, analysis and systematic design of the BFNs are given. The networks are designed and intended to be used mainly for low Sidelobe Level (SLL) linear Multibeam Antennas (MBAs). Several design examples are presented, along with fabrication and measurements of an S-band prototype.
In this paper we present seasonal results of the effective earth radius factor distribution in South Africa using recently (2007-2009) acquired radiosonde data from the South African Weather Service (SAWS) for seven locations in South Africa. Two data modeling methods are used to formulate the solution for the distribution of the effective earth radius factor. The seasonal effective earth radius factor statistics obtained from the radiosonde measurements are then interpolated, gridded and presented in contour maps to cover the rest of the country for the four seasons defined by ITU-R recommendation P.453-12. The Integral of Square Error is used to check the performance of the data modeling techniques while the Root Mean Square Error is used to compare the performance of the different interpolation methods used.