Current Issue : October - December Volume : 2012 Issue Number : 4 Articles : 6 Articles
This paper presents an ultra-wideband (UWB) rectangular ring antenna excited by a circular disc monopole (CDM) with a\r\nconducting rod and two double ridges to radiate bidirectional pattern with constant beam direction along the entire UWB\r\nfrequency range of 3.1ââ?¬â??10.6 GHz. The conducting rod and double ridges at the upper wall of the ring are added to solve the\r\ntilted beam problem at the higher edge frequency whereas the double ridges at the lower wall are used to enhance the impedance\r\nbandwidth. The dimensions of the rectangular ring and the CDM are initially considered to achieve the bidirectional pattern with\r\nthe suitable resonant frequencies and bandwidth. Then, the parameters of copper rod and two double ridges are determined by\r\nparametric study using CST Microwave Studio simulation software. The prototype antenna was fabricated, and the measured\r\nresults show good agreement with the simulated ones. The obtained bandwidth of |S11| < -10 dB can cover the UWB frequency\r\nrange as well as the bidirectional beam radiation with constant beam direction (? = 0?, 180? and f = 90?). The minimum and\r\nmaximum measured gains are 3.1 dBi to 5.3 dBi, respectively. The proposed antenna possesses compact size with good radiation\r\nperformance that can be a promising candidate for UWB applications....
The rapid and green formation of spherical and dendritic silver nanostructures\r\nbased on microwave irradiation time was investigated. Silver nanoparticles were\r\nsuccessfully fabricated by reduction of Ag+ in a water medium and using\r\npolyvinylpyrrolidone (PVP) as the stabilizing agent and without the use of any other\r\nreducing agent, and were compared with those synthesized by conventional heating\r\nmethod. UVââ?¬â??vis absorption spectrometry, transmission electron microscopy (TEM),\r\natomic absorption spectroscopy (AAS) and photon correlation spectroscopy (PCS)\r\nmeasurements, indicated that increasing the irradiation time enhanced the concentration of\r\nsilver nanoparticles and slightly increased the particle size. There was a lack of large silver\r\nnanoparticles at a high concentration, but interestingly, the formation and growth of silver\r\ndendrite nanostructures appeared. Compared to conventional heating methods, the silver\r\nnanoparticle suspension produced by irradiated microwaves was more stable over a\r\nsix-month period in aqueous solution without any signs of precipitation....
In this article, the design of conformal monopole antennas on a very thin layer of flexible liquid crystals\r\n(LCs) is introduced. The flexible LC substrate can be bent and folded over the module case, resulting in\r\na tight integration of the antenna with the frontend module. Firstly, a meander monopole antenna,\r\ndesigned for single band operation, is presented with details of the structure, simulation and\r\nmeasurement results. Secondly, a method to increase the peak gain and decrease the return loss of the\r\nantenna is proposed. The simulated results are compared with measured data, and good agreement is\r\nobtained....
An analytical approach to location and shape reconstruction of dielectric scatterers, that was recently proposed, is tested against\r\nexperimental data. Since the cross-sections of the scatterers do not depend on the z coordinate, a 2D problem can be formulated.\r\nA closed-form singular value decomposition of the scattering integral operator is derived and is used to determine the radiating\r\ncomponents of the equivalent source density. This is a preliminary step toward a more complete solution, which will take into\r\naccount the incident field inside the investigation domain in order to provide the dielectric features of the scatterer and also the\r\nnonradiating sources. Reconstructions of the equivalent sources, performed on some scattering data belonging to the Fresnel\r\ndatabase, show the capabilities of the method and, thanks to the closed-form solution, results are obtained in a very short\r\ncomputation time....
The large observation footprint of low-frequency\r\nsatellite microwave emissions complicates the interpretation\r\nof near-surface soil moisture retrievals. While the effect of\r\nsub-footprint lateral heterogeneity is relatively limited under\r\nunsaturated conditions, open water bodies (if not accounted\r\nfor) cause a strong positive bias in the satellite-derived soil\r\nmoisture retrieval. This bias is generally assumed static and\r\nassociated with large, continental lakes and coastal areas.\r\nTemporal changes in the extent of smaller water bodies as\r\nsmall as a few percent of the sensor footprint size, however,\r\ncan cause significant and dynamic biases. We analysed the\r\ninfluence of such small open water bodies on near-surface\r\nsoil moisture products derived from actual (non-synthetic)\r\ndata from the Advanced Microwave Scanning Radiometer\r\nfor the Earth Observing System (AMSR-E) for three areas\r\nin Oklahoma, USA. Differences between on-ground observations,\r\nmodel estimates and AMSR-E retrievals were related\r\nto dynamic estimates of open water fraction, one retrieved\r\nfrom a global daily record based on higher frequency AMSRE\r\ndata, a second derived from the Moderate Resolution Imaging\r\nSpectroradiometer (MODIS) and a third through inversion\r\nof the radiative transfer model, used to retrieve soil\r\nmoisture. The comparison demonstrates the presence of relatively\r\nsmall areas (<0.05) of open water in or near the sensor\r\nfootprint, possibly in combination with increased, belowcritical\r\nvegetation density conditions (optical density <0.8),\r\nwhich contribute to seasonally varying biases in excess of\r\n0.2 (m3 m-3) soil water content. These errors need to be addressed,\r\neither through elimination or accurate characterisation,\r\nif the soil moisture retrievals are to be used effectively\r\nin a data assimilation scheme....
Volumetric miniaturization, compactness, light weight, low cost, low loss, improved efficiency, multi band electromagnetic responses are the basic key design and application issues for any innovative technique used for microstrip filter. The current trend in the modern researches for microstrip filter is using the double negative metamaterial as a substrate to meet the stringent requirements. Naturally available conventional double positive dielectric (DPS) materials such as FR-4, PTFE, and Teflon have been popularly used as substrates on the cost of deteriorating the overall electrical performance of transceiver systems. These DPS materials have both the dielectric permittivity (ε) and magnetic permeability (µ) positive or zero. The recent wireless communication industry demands the microstrip filters designed using mu-negative (MNG), epsilon negative (ENG), single negative or double negative (DNG) left-handed electromagnetic materials having ε and/or µ less than zero replacing those having been designed using DPS. It can be achieved through the introduction of Split Ring Resonator (SRR) and rod structure in thin slab of naturally available DPS substrate. Mechanical design issues such as 2-D alignment and 3-D orientation, dimensions, spacing between SRRs and rods, number-size and density of unit cells placed in the DPS, and structural-materialistic properties deciding its electrical characteristics and the filter responses are focused. This proposed research work opens the paths for the future young aspirants to design and develop multi band miniaturized filters for the higher range of microwave regime....
Loading....