Current Issue : January - March Volume : 2015 Issue Number : 1 Articles : 7 Articles
In the last few years, there has been growing interest in employing meta materials (MTMs) to enhance antenna gain. In this paper\nwe proposed a novel structure of planar folded-line left-handed meta material (FL-LHM) and applied it to improve the gain of\nthree 5.8GHz micro strip antenna types: a circularly polarized patch antenna, an antenna array, and a beam steering antenna. The\nplanar FL-LHM structure was designed based on transmission line analysis. Their scattering parameters were obtained using a\nnumerical model; the negative effective permittivity and permeability were then calculated from these parameters for the assessment\nof negative refraction index region.The S11 and radiation patterns of three fabricated antennas were measured; these results matched\nwell with the simulation.We observed that the gain was increased up to 3 dBi for all the antennas. In addition, we were also able to\nmaintain the circular polarization as well as the steering of the antenna without changing its dimensions....
According to the characteristics of the polarizability in frequency domain of three commonmodels of dispersive media, the relation\nbetween the polarization vector and electric field intensity is converted into a time domain differential equation of second order\nwith the polarization vector by using the conversion from frequency to time domain. Newmark ???????? difference method is employed\nto solve this equation. The electric field intensity to polarizability recursion is derived, and the electric flux to electric field intensity\nrecursion is obtained by constitutive relation. Then FDTD iterative computation in time domain of electric and magnetic field\ncomponents in dispersive medium is completed. By analyzing the solution stability of the above differential equation using central\ndifference method, it is proved that this method has more advantages in the selection of time step. Theoretical analyses and\nnumerical results demonstrate that this method is a general algorithm and it has advantages of higher accuracy and stability over\nthe algorithms based on central difference method....
The impact of dielectric constant on radiation efficiency of embedded antenna located inside human body or another liquid\nenvironment is investigated both analytically and numerically.Our research is analysed and simulated at 403 MHz in the Med Radio\nband (401ââ?¬â??406 MHz) and within a block of 2/3 human muscle phantom. Good agreement is achieved between analysis and\nsimulation results. This work provides a guidance in selecting insulator for embedded antennas....
The combination of distributed antenna systems (DAS) and multiple input multiple output (MIMO) schemes opens the way to a\nvariety of coverage solutions for indoor environment. In this paper interleaved-MIMO (i-MIMO) DAS indoor coverage extension\nstrategies are studied. Their performance in high-order MIMO cases is investigated in realistic conditions through LTE-A link level\nsimulations, based on statistical data extracted from radio channel measurements; the impact of the deployment strategy\non performance is then evaluated and useful planning guidelines are derived to determine the optimum deployment for a given\npropagation environment....
We propose a new method to design miniaturized compact antennas, in which it is possible to control conjointly the radiation\nefficiency and the bandwidth selectivity of the antenna. And this method has been validated by the realization of prototypes based\non planar resonators. The geometry of these resonators has been chosen because their unloaded quality factor can be controlled\nand is mainly dependent on radiation loss. In the first time, a filter with a significant potential to radiation has been realized by\nchoosing suitable miniaturized resonators. An antenna, based on the same structure, in which the output of the filter was removed\n(load by air resistance) can be obtained. Modification of the quality factor of each resonator is necessary to take into account the\nchange of the load value from the previous filter to the final structure. The position and the quality factor of the resonators are\ndetermined by a filter design concept to obtain a specific frequency response in which each resonator is a basic radiation element.\nLoad of the antenna is ultimately a distributed load constituted by the parallel contributions of each resonators to radiation loss. In\nother words such an antenna can also be called radiating filter....
The strong desired signal will be mitigated due to ââ?¬Å?self-nullingââ?¬Â for the adaptive beam former, even if the array calibration is used.\nThe proposed methodology switches the models between phased array and adaptive array. In general, the system utilizes Frost\nadaptive beam forming. However, it will be switched to phased array if the ââ?¬Å?self-nullingââ?¬Â appears. According to the estimation of the\narray pattern at the direction of desired signal, we can determine if the ââ?¬Å?self-nullingââ?¬Â happens. The new approach is much easier to\nimplement compared with the various robust beam forming algorithms....
Radiation patterns emitted froma long-termevolution (LTE) base station antenna were first simulated by the finite-difference time\ndomain (FDTD) method. The validity of simulation results of radiation patterns was further checked by measurement data. After\nvalidating the accuracy of the FDTD method, electric fields at 123 test sites around a LTE base station in an urban area of Taipei\nCity were simulated. Simulated electric fields were also validated by comparison with measured data obtained by a high frequency\nselective radiation meter with an isotropic E-field probe. Simulated and measured electric fields are in the range of 0.104ââ?¬â??1.182 and\n0.098ââ?¬â??1.179 V/m at 1795MHz, respectively. From obtained electric field strengths, it is ensured that the urban area is a good signal\nenvironment. The maximum power density emitted from the LTE base station is about 1.853 Ã?â?? 10?4 mW/cm2 and is thus far below\nthe safety standard value of 1.197mW/cm2 for human exposure to RF radiation at 1795MHz....
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