Wideband circularly polarized square dielectric resonator antenna for WLAN/WiMAX applications

In the present article, a novel single fed square dielectric resonator antenna (SDRA) is presented and two orthogonal modes ( ${\mathrm{TE}}_{111}^{\mathrm{x}}\text{and}{\mathrm{TE}}_{111}^{\mathrm{y}}$) of SDRA are utilized to produce the wideband circular polarization. To generate circular polarization over a broad frequency band, a new technique known as hybrid DRA has been proposed in this article. In this technique, the feeding circuit act as a radiator and also provides feeding to the dielectric resonator which enhances the impedance and axial ratio bandwidth. A 3‐dB axial ratio bandwidth of 26.66% is achieved by the SDRA excited through a rectangular patch united with 50 Ω microstrip line. In order to further increase the axial ratio bandwidth from 26.66% to 48%, a notch is truncated from the rectangular patch. The design antenna prototype has been fabricated and experimentally tested. Experimental results illustrate that the proposed structure has broad impedance and axial ratio bandwidth of 75.86% and 43.75%, respectively, and the entire axial ratio bandwidth fully matched with the impedance bandwidth. The proposed antenna produces a right handed circularly polarized (RHCP) field. By taking the mirror image of the proposed microstrip feeding, the RHCP field is converted into left handed circularly polarized (LHCP) field. This antenna is preferred for wireless applications such as indoors communication, remote sensing, wireless sensor systems and WLAN/WiMAX applications.     

Compact ultrathin conformal metamaterial dual‐band absorber for curved surfaces

A compact, ultrathin conformal metamaterial dual‐band absorber for curved surfaces has been presented in this article. The absorber unit cell composed of circular and split ring resonators which are connected with plus‐shaped structure. The proposed absorber unit cell is compact in size (0.22λ_o × 0.22λ_o) and as well as ultrathin thickness (0.006λ_o), where λ_o is the wavelength at 5.8 GHz. The designed absorber gives two absorption tips at 5.8 and 7.7 GHz with more than 90% absorptivity. The full width at half maximum bandwidths are 220 MHz (5.67‐5.89 GHz) and 250 MHz (7.58‐7.83 GHz). The proposed conformal absorber is sensitive to the polarization angle and has a stable absorptivity over a wide range of incident electromagnetic wave. The parametric analysis and equivalent transmission line model have been investigated. The surface current and electric field distribution also discussed for understanding the absorption mechanism. To analyze the performance of proposed absorber on the curved surfaces, it is wrapped on the different radius of cylindrical surface and measured the absorptivity. Simulated and measured results have good agreement between them.     

Hybrid two segments ring dielectric resonator antenna for ultrawideband application

In this article, a hybrid two segments ring dielectric resonator antenna with partial ground plane, for ultrawideband application is described. The proposed antenna structure consists of annular shape microstrip line along with two ring dielectric resonators having different permittivity. By applying the combination of shifted annular shape microstrip line (used as a radiator as well as to convert TM_01δ mode to TE_01δ mode) and two segments ring dielectric resonator, ultra wide bandwidth has been achieved. Prototype of proposed structure has been fabricated and tested. Measured results show good agreement with the simulated ones. The proposed antenna structure operates over a frequency range of 3.45‐10.9 GHz with a fractional bandwidth of 103.83% and having better gain and radiation characteristics. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:47–53, 2016.     

Compact dual‐band ring dielectric resonator antenna with moon‐shaped defected ground structure for WiMAX/WLAN applications

In this article, compact ring‐shaped dielectric resonator antenna (DRA) along with moon‐shaped defected ground structure (DGS) was studied. The proposed antenna was fed by microstrip line shifted from center position, which excited TE_01δ mode in ring DRA. Moon‐shaped DGS was acting as a radiator and also reduced the size of proposed antenna by an amount of 14.87% (lower frequency band) and 48.77% (upper frequency band). The proposed antenna was designed to resonate at two different frequencies namely 2.24 and 5.82 GHz with a fractional bandwidth of 30.17% and 22.14%, respectively. Based on optimized design parameters, archetype of antenna structure has been constructed and measured successfully, which shows good agreement with simulated ones. The proposed antenna design was suitable for WLAN (2.4/5.2/5.8 GHz); WiMAX (2.5/5.5 GHz); AMSAT (5.6/5.8 GHz); and WAVE (5.9 GHz) bands. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:503–511, 2016.     

Enhanced Strength in Cu-Ag-Zr Alloy by Combination of Cold Working and Aging

In this investigation, the effect of different degree of cold rolling and post-aging treatment on the microstructure and mechanical properties of a Cu-3wt.%Ag-0.5wt.%Zr alloy was studied by means of hardness measurement, tensile tests, optical and electron microscopy. The alloy was subjected to cold rolling up to 80% followed by aging in the temperature range of 400-500 °C. The yield strength, ultimate tensile strength and hardness were found to increase as degree of cold rolling increased, but at the expense of ductility. Aging of cold rolled samples in the studied temperature range has resulted in different combinations of strength and ductility. However, aging of cold rolled samples at 400 °C for 1 h has resulted in a combination of high strength and moderate ductility. A yield strength and ultimate tensile strength of 511 and 560 MPa, respectively with a ductility of 12% were achieved for 80% cold rolled and aged (400 °C for 1 h) sample. The high strength achieved after 80% cold rolling and aging is mainly attributed to precipitation of fine silver precipitates.     

Cylindrical Dielectric Resonator Antenna Terminated in a Phantom Muscle Medium

In this paper, the simulation and experimental studies of input characteristics as well as near field distribution of cylindrical dielectric resonator antenna (CDRA) and specific absorption rate (SAR) distribution in a homogeneous phantom muscle medium in close proximity with the antenna are reported in C-band of microwave frequencies. The simulation study has been carried out using Ansoft HFSS 3-D simulation software. The experimental SAR distribution has been obtained using two 50 $\Omega $ L-shaped and straight coaxial probes and Agilent make 3 Hz–50 GHz spectrum analyzer. The simulated results for input characteristics of the CDRA and SAR distribution in the phantom muscle medium due to the antenna are compared with the respective experimental results.     

Four Element Wideband Rectangular Dielectric Resonator Antenna Terminated in a Bio-medium

In this paper, a new four element rectangular dielectric resonator antenna (RDRA) for 5.0 GHz WLAN/WiMAX band is proposed. The simulation results for its radiation characteristics and the specific absorption rate (SAR) distribution in a homogenous bio-medium (muscle layer) for different antenna-to-muscle layer spacings are presented at different frequencies in 4.9–5.9 GHz band. The input characteristics of the proposed antenna and a single element RDRA of same size as the element are compared. The effect of changing antenna input power on maximum SAR value is also analyzed. The simulation study has been carried out using CST Microwave Studio software.     

Layer average relative humidity from SAPHIR on board Megha-Tropiques: validation with numerical model analyses

Subsequent to the launch of the Sondeur Atmosphérique du Profil d’Humidité Intertropicale par Radiométrie (SAPHIR) sensor on board the Megha-Tropiques satellite on 12 October 2011 from Satish Dhawan Space Centre, Indian Space Research Organization (ISRO), Shriharikota, India, the validation of layer averaged relative humidity (LARH) retrieved from SAPHIR has been initiated in different phases along with other retrieved parameters. The Megha-Tropiques is a joint satellite mission executed by the Indian Space Research Organization (ISRO) and the Centre National d’Etudes Spatiales (CNES), and is primarily devoted to study the tropical atmospheric processes influencing both weather and climate. The present study focuses on a validation campaign, where the validation of LARH derived from SAPHIR is carried out with three different numerical model analyses: the European Centre for Medium Range Weather Forecasts (ECMWF) model, the National Centers for Environmental Prediction (NCEP) model, and the National Centre for Medium Range Weather Forecasting (NCMRWF) model, over a period of six months from January 2013 to June 2013. It is observed that the root mean square difference (RMSD) of LARH has improved considerably for layers 1, 2, 3, and 6, and some marginal changes for layers 4 and 5, when a bias correction is applied to the data. The RMSD of SAPHIR LARH after correcting for bias is well within the range of the mission goal of 20% accuracy.     

Partitions based computational method for high-order fuzzy time series forecasting

In this paper, we present a computational method of forecasting based on multiple partitioning and higher order fuzzy time series. The developed computational method provides a better approach to enhance the accuracy in forecasted values. The objective of the present study is to establish the fuzzy logical relations of different order for each forecast. Robustness of the proposed method is also examined in case of external perturbation that causes the fluctuations in time series data. The general suitability of the developed model has been tested by implementing it in forecasting of student enrollments at University of Alabama. Further it has also been implemented in the forecasting the market price of share of State Bank of India (SBI) at Bombay Stock Exchange (BSE), India. In order to show the superiority of the proposed model over few existing models, the results obtained have been compared in terms of mean square and average forecasting errors.     

Dual port aperture coupled MIMO cylindrical dielectric resonator antenna with high isolation for WiMAX application

In this article, a dual port aperture coupled MIMO cylindrical dielectric resonator antenna with enhanced isolation is proposed. Dual feeding techniques are used to excite dielectric resonator. These feeding structures are oriented in such a way so that they can produce orthogonal mode in the dielectric resonator. High isolation is observed by generating two orthogonal modes, that is, and in the dielectric resonator. The fractional bandwidth for port 1 and port 2 is 17.8% (3.1‐3.68 GHz) and 18.4% (3.1‐3.7 GHz), respectively, and isolation between the two ports exceeds ?25 dB within the required band. The proposed antenna is simulated, fabricated, and experimentally tested. Good agreements between measured and simulated results are observed. The various diversity performance parameters are also lie within their acceptable limits. Based on presented results, it can be concluded that the presented MIMO antenna is suitable for WiMAX (3.3‐3.6 GHz) applications.