Wyniki 1-3 spośród 3 dla zapytania: authorDesc:"Thanh Nghia Cao"


  1. INTRODUCTION In recent years, multi-antenna technology has been interested and widely applied in wireless communication systems. This technology uses multiple antennas for both transmitting and receiving sides. The antennas at the communication circuit terminals are combined to minimize errors and optimize data rates. In fact, the diversity system antennas can exist as MISO (Multiple Inputs Single Output), SIMO (Single Input Multiple Outputs), or most complicated system, the MIMO (Multiple Inputs Multiple Outputs) [1-2]. In a MIMO system, the antenna designs, the most concerned parameters are the resonant frequency, the radiation pattern, and in addition, the interaction/ coupling effect between multi-elements of the antenna array is also concerned [3]. In order to satisfy this requirement, the MIMO system antenna the separation of the elements need to be the half wavelength of the lowest operational resonant frequency. However, this makes the overall size of the MIMO system antenna terminals increased significantly. This leads to the urgent need of researching and designing of MIMO system antennas for radio communication systems, which are compact in size but still ensure isolation coefficient less than 10dB between elements. Therefore, in recent times, many antennae of MIMO system have been proposed to be applied in new information systems such as mobile phones, handheld device[...]


  Nowadays, science and technology develops rapidly, what allow multiple communication systems to be integrated on the common platform in such devices as cellular system handset, PDA, tablets etc. In fact, there are many communication systems, like GSM, UMTS, LTE, WLAN, Bluetooth, GPS (see Table 1), which sited on one device could help mobile user. The devices, used often in mobile applications, should operate in multiband frequencies, and simultaneously be small, compact as well as be possible light. Tab. 1. Data of Modern Communication Systems Systems Frequency, GHz Bandwidth, MHz GSM 0.89-0.96 35 1.71-1.88 170 GPS L2: 1.2276 11 L1: 1.57542 15.345 L5: 1.17645 12.5 UMTS 0.9 / 2.1 60 LTE 2.10 5, 10, 15, 20 1.90 1.4, 3,5,10,15,20 WLAN 2.43 20 5.0 22 TV Satellite C-band 4 36 6 36 Bluetooth 2.4 1 Such systems required special design of receiving/ transmitting antennas. Nowadays there many methods to design it have used. In most cases they are realized in the microstrip-line technology, integrated on common board with the active devices. Since second half of 20th age the fractal geometry is considered as potential support in the design of such antenna [1], [2], [3]. In the paper the fractal geometry applied to antenna design is introduced. In following chapters the fractal geometry, parameters and design procedures are shortly described. Next some useful fractal shapes are used into antennas design for use in different mobile communication systems. 2. FRACTAL GEOMETRY Fractal geometry is described by B. Mandelbrot [4] as a rough or fragmented geometric shape that can be separated into parts which approximate the whole geometry but in a reduced size. The fractal geometry is used a lot in life [5], due to fact if it could better describe the complex objects than conventional Euclidean one, which is limited to the lines, points, sheets and volumes. The study of fractal geometry in combination with the electromagnetic [...]


  1. INTRODUCTION In recent years, along with the development of wireless communication technology, the performance of the antennas in these systems demand must also in-crease. There are many methods for increase of the performance of the antenna have been using. One of them is using metamaterial structures for antenna design, which has been attracting the designers [1]. In recent decades, a study of metamaterials for application in the field of science and technology has achieved great success. Metamaterials have been applied effectively in life, one of which is the use of metamaterials structures for antenna design. In 1968, the scientist Vaselago [20] studied a material which had, simultaneously, negative permeability ( ) and permittivity ( ) on a certain frequency band. He termed this material such as media left-hand (LH) which r, magnetic field vectors, and phase propagation vectors [2]. However, these properties are not available in natural materials but only in artificial materials called metamaterials. Metamaterials (MTMs) are understood as an artificial material that is created by arranging homogeneous metal structures and having unusual properties that natural materials are not available. The size of an effective homogeneous structure to form a unit cell of metamaterials must be much smaller than the guided wavelength [3]. Metamaterials are designed by arranging microstructures that are called "cells". These "cells" can be made from electrical, non-electrical or dielectric materials. These structures may be symmetric or asymmetric, isotropic or anisotropic. The arrangement of atoms can be in an orderly or chaotic manner, the purpose of which is to create the desired macro characteristics for the metamaterial. On the other hand, different structures give different types of metamaterials and applications, which are classified based on the permittivity and permeability values created by those structures [4]. 2. CLA[...]

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