This paper discusses the variation of ionospheric Total Electron Content (TEC) over low latitude Indian region, Hyderabad station (Lat: 17.39oN, Lon: 78.31oE) for geomagnetic quiet and disturbed days during the low solar activity period (2017 year) of the 24th solar cycle using global ionospheric models and experimental NavIC (Navigation with Indian Constellation) data. The work mainly focuses on the performance of the IRI Plas 2017 (International Reference Ionosphere) model with and without assimilation of TEC input, GIM TEC (Global Ionospheric Maps) and IRI 2016 models. In order to evaluate the performance of the models, the diurnal, monthly, and seasonal variations of Vertical TEC (VTEC) are predicted and compared with Indian regional NavIC data. From the result analysis it is observed that smaller Root Mean Square Errors (RMSEs) between NavIC VTEC and modelled VTEC are found in June and December solstice months than March and September equinox months. The VTEC predicted by the IRI Plas with assimilation of TEC input option produced smaller estimation errors than IRI Plas without assimilation of TEC input and IRI 2016 model. The same analysis has been tested for geomagnetic storm occurred during 7-9 September, 2017 for different locations. The IRI Plas 2017 with TEC input option exhibits better performance than IRI Plas and IRI 2016 models. Therefore, the VTEC predictions by assimilation of optional inputs will be helpful in applications of ionspheric studies to predict the dynamics in the ionosphere particularly for the period of disturbed geomagnetic conditions.
This paper presents an efficient method to redesign a horn-fed, double-curvature reflector antenna. It helps reconstruct or repair the reflector according to a correct reference or analyze its radiation characteristics through full-wave electromagnetic simulations. The proposed method mainly consists of five stages. At first, it is necessary to obtain initial data in the form of three-dimensional coordinates of a sufficient number of points sampled from the reflector's different surface areas, especially from its central section curve and its peripheral contour. Then, the best-fitting surface to the sampled points is found using geometrical-optics (GO)-based formulations in an invasive weed optimization (IWO) algorithm. The GO relations extend the reflector laterally using elevation angle, horizontal, or focal point strips. As these are intrinsic formulations for designing doubly-curved reflectors, the fitted surface can resolve the possible defects in the reference reflector's geometryor inaccuracies in the sampled information partly. For this purpose, the reflector's central section curve is estimated by fitting a fifth-degree polynomial curve to the data sampled from it. Also, two kinds of errors, which are based on Euclidean distances, define the optimization algorithm cost function for more reliable surface fitting. In the third stage, the fitted surface's peripheral contour is adjusted to match the outline of the reference reflector using the points sampled from this section. In stage four, the redesigned reflector in the form of a point cloud is converted to a .stl file format for further simulation in a full-wave electromagnetic software. Finally, the similarity between the redesigned and reference reflectors' radiation patterns is examined using a radiation-based cost function in an iterative process, and the previously devised four stages repeat until appropriate results are obtained. In particular, an already designed and fabricated UHF band, doubly-curved reflector antenna, capable of generating a cosecant-squared radiation pattern in the elevation plane and narrow in the azimuth, is redesigned using 99 points sampled from it. It is found that horizontal strips can best fit the reflector with the small normalized error about 3 mm at the end of the IWO algorithm, indicating a nearly perfect geometrical similarity between the redesigned and reference reflectors. For further verification of the suggested method, the redesigned reflector's radiation pattern is simulated in CST simulation software, and the results are compared with the measured radiation pattern of the fabricated reflector and the simulated radiation pattern of the antenna's initial CAD model in the azimuth and elevation planes. Specifically for the redesigned antenna, the amounts of HPBW and sidelobe level in the azimuth plane are about 2.6° and 29.85 dB, respectively. Also, the amounts of gain, HPBW, and predefined parameters of α and β in the elevation plane are 28.25 dB, 13.5°, 5.07 dB, and 11.7°, respectively. All of the measured and simulated results are in good correspondence with each other, suggesting that the proposed method is a secure solution for redesigning double-curvature reflector antennas precisely and efficiently.
Valve radiator blockage is a serious problem endangering the safety of thyristor. At present, there are no effective methods for blockage evaluation and monitoring. This paper analyzes the heat dissipation state of a radiator under different blocking conditions and divides it into abnormal heat dissipation and normal heat dissipation. Then, based on reliability theory, the tolerance index ψ for blockage and the probability index θ for overheating are proposed to evaluate the blockage hazard of the thyristor. Also, the thermal circuit model of the valve group is established to monitor radiator blockage. According to the model, the corresponding relationship between radiator blockage and valve temperature distribution is solved, and the blockage detects index
RAdio Detection And Ranging (RADAR) is an essential tool used extensively to detect a target's presence within the vicinity characterized by the range of the RADAR. In order to localize the target, Direction of Departure (DOD) and Direction of Arrival (DOA) estimations are utilized. To make it more convenient, a bistatic multiple input multiple output (MIMO) configuration is exploited to deduce the position of a target through the triangulation method easily. Furthermore, due to the maneuvering of targets in space, more robust direction finding solutions can be derived using Time-Frequency (TF) representations. Thus, this paper aims to leverage the benefits of TF analysis for the estimation of DOD and DOA jointly for a bistatic MIMO radar. The performance of the considered method is numerically evaluated and is compared against the conventional algorithms that do not use TF tools and as well compared against the Cramer Rao Lower Bound (CRLB). The results show that TF based approach may be a promising candidate in terms of its robustness against channel noise. Also, the performance of the TF based DOD-DOA estimates is studied in terms of their consistency and resolvability of targets which measures the performance in a multi-target environment. Finally, the use-case of TF based estimation to solve the problem in the presence of coherent targets is analysed through simulations and inferred.
Beamforming can steer the mainlobe of the beam pattern towards the desired signal and set several nulls in the directions of interference signals by adjusting the excitation weights of array elements. These days, a range of meta-heuristic algorithms have been utilized for beamforming of antenna arrays. However, most of the methods are applied to linear arrays and rarely to planar arrays. In this paper, a novel variant of binary particle swarm optimization (BPSO) is proposed at first, where the global search ability and the local optimization ability are both taken into account. Then, the fitness function including the term of peak sidelobe level (PSLL) is constructed, and the improved BPSO is applied to the beamforming of uniform planar array (UPA). Finally, simulation results demonstrate that the proposed algorithm is not only able to suppress PSLL effectively, but also able to form deeper nulls than that of linearly constrained minimum variance (LCMV).
Nowadays, due to the ever-increasing number of electronic devices and communication systems that use high-frequency electromagnetic waves, a significant level of electromagnetic energy is available in the environment that is not entirely used. In this work, a complete electromagnetic harvesting system using a rectenna is proposed to collect this energy and feed a temperature measurement module. The rectenna is constituted by a combination of a microstrip antenna that captures the electromagnetic energy and a rectifier circuit that converts it into electric energy in direct current (DC) form to feed ultra-low-power loads. The proposed system uses a rectangular microstrip antenna, designed and optimized by using the Computer Simulation Technology (CST®) software to operate at 2.45 GHz. This designed antenna presents a measured reflection coefficient lower than -20 dB at the operating frequency with a maximum gain equal to 7.26 dB. In addition, a voltage doubler rectifier circuit is designed and optimized by using the Advanced Design System (ADS®) to match the impedance of the designed antenna to reduce the reflection losses between these two modules, achieving maximum measured efficiency of approximately 33%. Furthermore, a boost converter circuit is designed for the power management between collected and delivered powers to the sensor and to provide appropriate voltage levels to feed the temperature measurement module. This module consists of an ultra-low-power microcontroller and a temperature sensor that operates in the range of 1.8-3.6 V. The procedures for designing and testing each module of this system are detailed. Finally, a prototype is built and tested under different operating conditions to confirm its functionality and feasibility. These tests show that the proposed system can operate without batteries, only with the harvested electromagnetic energy dispersed in the environment, even from modulated and pulsating sources, as is the case of commercial routers.
This paper presents a paattern synthesis method to generate dual-beam patterns of a rectangular planar array of isotropic antennas in a particular scanning angle using Evolution Algorithms. The dual-beam patterns are cosec2 pattern and pencil beam pattern, and both the patterns are steered to an elevation angle of 20 degrees (θ = 20˚). Moreover, each pattern is synthesized in three azimuth planes (φ = 0˚, 5˚, and 10˚). The isotropic elements are uniformly spaced, and nonuniform excitations are applied to achieve the desired patterns. These patterns are obtained by applying the optimum set of common elements amplitude and phases for the cosecant-squared pattern only. The optimum 4-bit discrete amplitudes and 5-bit discrete phases are produced using using Differential Evolutionary (DE) Algorithm, Genetic Algorithm (GA), Particle Swarm Optimization (PSO) Algorithm, and Firefly Algorithm (FA). These discrete excitations are helpful to reduce the Dynamic Range Ratio (DRR) and the design complexity of the feed networks. The excitations are also verified in a range of arbitrarily chosen azimuth planes. The patterns are generated in the same steering angle with minor variations of the desired parameters. The outcomes established the superiority of DE over PSO, GA, and the effectiveness of the proposed method.
This article reports a multilayer implantable biosensor for a continuous glucose monitoring system, tested on rats to determine the relationship between intravenous glucose level and resonance frequency of implant antenna sensor. An implantable antenna sensor with the volume 330.9 mm3 is tested in three rats as an animal model. This antenna biosensor operates in the Medical Implant Communication Service frequency band (402-405 MHz) with the simulated and measured maximum gains of -13.33 and -21.1 dB, respectively. The specific absorption rate obtained is within the standard limits. An oral glucose tolerance test is proposed to obtain the variation in blood glucose level in the animal's body during measurement. The resonance frequency shift and the corresponding blood glucose level are observed at a regular interval of 30 minutes. A frequency shift of 4.94 kHz per mg/dL is observed. Also, the results related to the reflection coefficient and the factors affecting sensor performance are discussed. The biosensor performance is validated using the proposed simple linear regression model.
An electrically small ultra-wideband (UWB) antenna to cater to the need for UWB communication suitable for today's small gadgets is presented. The antenna is realized on a substrate of relative dielectric permittivity 4.4, loss tangent 0.02 and height 1.6 mm. The overall dimension of the antenna is 21 mm×16 mm×1.6 mm (0.217λmin×0.165λmin×0.0165λmin), where λmin is the wavelength corresponding to the antenna's lowest operating frequency in free-space 3.1 GHz). The small `kmina' value of 0.856 of the antenna, where kmin is the wavenumber corresponding to λmin, and `a' is the radius of the sphere that can fully enclose the antenna, is electrically small. The antenna operates at the FCC recommended UWB frequency range from 3.1 GHz to 10.6 GHz with a reasonably good 2:1 voltage standing wave ratio (VSWR) impedance bandwidth. A prototype of the proposed antenna is fabricated, and different radiation characteristics of the antenna in the frequency and time domain are measured and validated by simulation. The high pulse fidelity for different antenna orientations and very small group delay in the operating frequency band exhibit insignificant pulse distortion. The equivalent isotropically radiated power (EIRP) of the antenna satisfies the FCC mask in the entire UWB. The maximum gain and efficiency achieved within the UWB are 3.95 dBi and 93% respectively. Radiation characteristics of the antenna in the UWB are studied in an anechoic chamber using Agilent PNA E 8362B.
Broadband variations of a proximity fed circular microstrip antenna gap-coupled with narrow annular sectoral patches are proposed. The gap-coupling of pairs of parasitic annular sectors along the x- and y-axes of the fed patch tunes the spacing in between the fundamental modes on the respective patches that yields wider bandwidth. A maximum bandwidth of 728 MHz (55%) offering peak gain of nearly 9 dBi is obtained in the circular patch gap-coupled with four pairs of annular sectors along the x-axis. This bandwidth is around 13% larger than the bandwidth offered by a single circular microstrip antenna. Instead of using multiple sectoral patches, a gap-coupled design of circular patch with a stub loaded annular sectoral patch is presented. The stub tunes TM02 mode frequency with reference to the fundamental modes on the circular and sectoral patches that yields bandwidth of 660 MHz (51%). Resonant length formulation and subsequent design methodology for all the proposed gap coupled configurations are presented, which helps in the re-designing of similar antennas at the given fundamental mode frequency. All the optimum and re-designed antennas are fabricated, and the measured results shows close agreement with the simulations.
In this paper, a novel low-profile and dual-polarized antenna is presented. The antenna is composed of two pairs of rhombic dipoles excited by two orthogonal baluns. The broadband characteristic is achieved by introducing a metal ring under the rhombic dipole, and the radiation pattern beam widths are also improved. Based on the antenna unit, a 2-element antenna array is designed, fabricated, and measured. The relative bandwidth (standing wave less than 1.5) of the antenna is 45.1%, and the port isolation is greater than 27 dB, whereas the cross-polarization level maintains lower than 16 dB in the the frequency band of 2.4-3.8 GHz. The measured results are in good agreement with the simulated ones. This proposed antenna also has low profile characteristics, and the profile height is 20.8 mm, which is less than one quarter of the wavelength (24.2 mm) of the central frequency point (f = 3.1 GHz).
A dual-band Wilkinson power divider covering comprehensive frequency ratios with improved Out-of-Band rejection is proposed with the use of only a resistor. In millimeter-wave range, the established lumped element based design with a wide range of frequency ratio suffers from the nonexistence of tiny required values and the difficulties of integrating them in the proposed designs. To tackle some of the more common millimeter-wave frequency bands challenges, the RLC is substituted in the design by transmission lines and a single resistor. The design parameters and rules are derived theoretically using even/odd mode analysis, and it takes into consideration the Out-of-Band performance. For validation, three different dual-frequency bands are studied (5.8-28 GHz, 20-35 GHz, and 28-35 GHz). The simulated and experimental results exhibit all the advantages of the proposed Wilkinson power divider, succeeding in boosting multi-functional and multi-standard RF and mm-wave front-ends for communication systems.
In this paper, a novel mechanical-flux-weakening interior permanent magnet (MFW-IPM) machine is proposed to improve flux-weakening ability. The key of the proposed machine is that the permanent magnet is rotatable, and a mechanical device is equipped on both sides of the rotor. The mechanical device can regulate the air-gap magnetic field by rotating PM to change the leakage flux and magnetization direction of PM. As a result, the flux-weakening ability is improved. The flux-weakening principle of the MFW-IPM machine is investigated in detail. In addition, a multi-objective optimization method is adopted to improve the performance of the proposed machine. Then, the electromagnetic performances of the original machine and optimized machine are compared by finite element analysis. Finally, both simulation results and experimental tests verify the effectiveness of the flux-weakening enhancement design and optimization method.
This paper presents a new integro-differential coupling between partial equivalent electrical circuits (PEEC) and finite difference method (FDM) taking into account the magnetization effect. This coupling is intended for thin plates having simultaneously significant conductive and magnetic properties in presence of exciting coils of complex topologies. These cases exist in eddy current nondestructive testing (ECNDT), eddy current separation, induction or levitation melting devices and more other applications. The choice of FDM, is in relation with rectangular surfaces generated by numerical meshes leading to mathematical integrations of magnetic and electrical quantities with independent variables, unlike more complicated forms of surfaces generated by finite element method (FEM) or others. Fully successful analytical expressions have been realized and implemented in overall coupling process. The PEEC method is mainly used to calculate the magnetic field applied to the nodes of the plate from different inclined polygonal coils. The results of magnetic field and eddy current distributions on thin plates are presented, and parts of them are compared with those realized by Flux 3D software.
Multilayer grid polarizers for millimeter waves produced with photolithographic technology have been simulated. Polarizers have spectral bands of enhanced performance where polarization extinction ratio in decibels grows in proportion to the number of layers. Full-wave modeling is compared with three asymptotic models for subwavelength gratings using adjusted grating parameters. Random variations of interlayer spacings reduce the enhancement of polarizing performance, yet the latter continues to grow in proportion to the number of layers. Broadband signal detection is also considered.
This paper proposes a novel bandpass filter for L-band based on CRLH TL, which is mainly formed by coupling a high-pass characteristic module with a low-pass characteristic module in a cascade. The high-pass module consists of an interdigitated coupled line and a grounding via, owning to its singular characteristics, which the miniaturization is realized. The low-pass module is composed of a C-type resonator with high-low impedance lines, which can realize great sideband attenuation characteristics. To further improve its out-of-band rejection characteristics, a complementary split-ring resonator (CSRR) defective ground structure with single-pole attenuation characteristics is loaded, and a transmission zero is introduced at 2.5f0 out-of-band. The test results are in great agreement with the simulation ones, and the dimensions are only 0.20λg*0.22λg. Compared with other similar types, the filter proposed in this paper has miniaturization, great passband selection characteristics, stopband characteristics, and the advantage of low insertion loss.
A new compact nonuniform leaky-wave antenna (LWA) with left-handed elliptical polarization (LHEP), based on composite right/left-handed (CRLH) metamaterial operating in the range of 7-10.2 GHz is presented in the work. The nonuniform structure of a CRLH transmission line (TL) is realized by the placement of different configurations of inter-digital capacitor (IDC) in the form of sinusoid (SIN-IDC), on the top of metal wall of a half-mode substrate integrated waveguide (HMSIW). Balanced condition of the unit cells is provided by the change in slit width, amplitude and the number of SIN-IDC periods, as well as by relocation of two additional transition apertures arranged by both sides of SIN-IDC. Based on the known Hensen-Woodyard criterion, the optimal number of the unit cells was determined, when the gain coefficient varied from 7.5 to 9.8 dB in all of the operational range of antenna. The developed prototype of nonuniform CRLH LWA has the size of 8.1x115.2 mm. It is characterized by a continuous scan angle range equal to 117°. The maximum angle of rotation radiation pattern is -66° for backward radiation and +51° for direct radiation. The maximum efficiency of the antenna radiation is 85%, while the total one is 68%.
When a substation is struck by lightning, it will cause the ground potential to rise, which will further cause serious interference to the secondary cable. This article is based on the grounding grid established in the testing ground. The grounding copper bar is laid in the cable trench to connect with the grounding grid. At different grounding grid points, use a lighting current impulse generator to apply high current. At the same time, the grounding grid model is established by using the ATP-EMTP software. Through the combination of test and simulation, the influence of different lighting inflow locations on the protection effect of grounding copper bar is studied, and combined with the connection method of the grounding copper bar and the grounding grid, the protective effect of the grounding copper bar on the secondary cable under the impact of lightning current was analyzed. The research results showed that the laying of grounding copper bars can reduce the influence of interference voltage on the secondary cables under certain circumstances, but when there are multiple connection points between the grounding copper bar and the grounding grid, the current injection position is different, which will affect the voltage between the cable core and the shielding layer. At the same time, it will also affect the ground potential rise of cable grounding point in different degrees.
A 6-element MIMO antenna system is introduced in this paper for N77, N78, and N79 (5G) communication bands. The proposed antenna element is composed of a four-section coupled line folded antenna. The performance of this antenna element is improved by using a partial ground plane combined with the DGS between the different elements of the MIMO antenna. The separated single antenna in this case has a reflection coefficient less than -10 dB over the frequency band from 3 GHz to 5 GHz. For the complete MIMO configuration, the reflection coefficientis less than -7 dB over the same frequency band for all the antenna elements. On the other hand, the isolation between antenna elements in the MIMO configuration is greater than 15 dB. The values of the MIMO parameters are calculated. These parameters include the Envelope Correlation Coefficient between the different elements (ECC), Diversity gain (DG), Total Active Reflection Coefficient (TARC), Channel Capacity Loss (CCL), and Mean Effective Gain (MEG). Good results are obtained for the MIMO parameters where ECC < 0.006, DG = 10, TARC < -7, CLL < 0.6, and -3 < MEG < -8. These performance parameters of the proposed MIMO system indicate that this antenna is suitable for 5G applications. The effect of the human hand on the S-parameter is also investigated. The proposed antenna is fabricated and measured to verify the simulation results.
A bidirectional, circularly polarized antenna with a miniaturized design and broadband capabilities is proposed for consideration in WLAN 2.4/3.65-GHz, WiMAX 2.3/2.5-GHz, 4G, and 5G frequency bands. The frontside of the antenna consists of a hexagonal slot, a hexagonal patch, ten meander tips, and rectangular corner notches to achieve broad impedance and axial ratio bandwidth. The feedline on the backside of the antenna with accompanying shorting pin is offset to further increase the common bandwidth. Also, the four corners of the antenna substrate are removed to decrease the electrical size. The designed antenna is fabricated and measured to validate simulation results. From measured results the antenna has a -10-dB impedance bandwidth of 89.7% (1.60-4.20 GHz) and a 3-dB axial ratio bandwidth of 70.5% (1.80-3.76 GHz). The peak realized gain in the boresight direction is 3.65 dBi, which occurs at 1.88 GHz.