Design Of A High Gain Micro-strip Antenna Array

As the key components of the wireless communication systems, the basic function of antenna is to receive and radiate electromagnetic wave. Antenna is a device to convert high-frequency electromagnetic energy into electromagnetic waves in free space or convert electromagnetic waves into high-frequency electromagnetic energy. In application the basic requirement of the antenna is to convert guided wave energy into electromagnetic energy as far as possible , that means , the efficiency of the antenna must be high , so the feed of the antenna feed network should be matched as much as possible . The antenna should also concentrate the electromagnetic wave to the required direction as much as possible, or absorb electromagnetic wave from the required direction as much as possible , which requires a good directional antenna . The antenna should also have sufficient bandwidth, and fit polarization form, dimensions and other requirements.Micro-strip antenna is often chosen in applications. It has small size, light weight, thin profiles, etc. But as the basic properties, the efficiency and direction of one single micro-strip antenna are very difficult to do well. In order to solve this fundamental problem, pose a number of micro-strip antenna arrays, has become a common solution.Radio frequency identification technology arose in the 90's of the 20th century. The radio frequency identification systems achieves non-contact transmission of information through space coupled (alternating magnetic field or electromagnetic field) radio frequency signal and achieve identification purpose through the transferred information. Products of modern society are more and more abundant, and the demand for data management has become higher.People need mark, identify and position items in process of production, marketing and circulation. Because the radio frequency identification systems use penetrating radio frequency identification, it will be a more long-range identification, no need for manual intervention, and it can identify a wide variety of items. In radio frequency identification systems, the antenna is a bridge among the identification tags, receiving system, processing software which plays an important role. In the passive-type tag system of radio frequency identification, tags obtain energy from reader's electromagnetic fields or electromagnetic waves to active the tag chip, in this case, the gain of the antenna should be as high as possible. In this paper, a micro-strip antenna array which works in 2.45GHz frequency is designed based on needs of long-range radio frequency identification and the structure design is improved.The works of this paper are below:First of all, it expatiate the micro-strip antenna and antenna array's basic theory and basic steps of design of micro-strip antenna, in accordance with the above knowledge rectangular patch antenna sizes, dielectric permittivity and other basic parameters are chosen and calculated, so that the basic antenna element is determined. According to the micro-strip matching circuit theory, design a single-side matching circuit and calculate the size of the various parts of the match network, and design the structure of the parallel feed network based on the characteristics of antenna arrays and adjust the feed circuits and matching circuits to reduce the coupling. Based on the structure of the antenna array element and the matching network, the feed network, design an eight elements uniform linear array with the elements feed by same amplitude and phase circuit.Then, use the high frequency simulation software HFSS, model the structure of the designed antenna and then scan spacing among the antenna array elements to obtain performance data under all the spacing of antenna array element to find array element spacing which can get the maximum gain. Under this spacing of the antenna array, analyses the gain, impedance, directivity, and bandwidth and discuss impact factors of various parameters of the antenna. Through simulation, confirm spacing of slightly less than half of the wavelength of the antenna array to meet the design needs. The final parameters of the antenna are as follows: the center frequency is 2.45GHz, the largest gain G is 23.12dB, the input impedance is 53.75 + j6.39, the input reflection coefficient is - 22.94dB, the 3 dB bandwidth B is 30MHz, the relative bandwidth is 1.25%.Finally, based on analysis of the linear array structure and performance, put forward the eight elements linear array into a four lines two rows planar array and then model structure of the array in the simulation software. For planar arrays, change the row spacing and simulate the structure to get the spacing under the best gain. Under the maximum gain spacing of the antenna structure, analyze the gain, directivity and other performances, and compare the planar array with the linear array to determine the factors which impact the performance of antenna array.According the simulation results of linear array and planar array, these can be concluded: in the mutual spacing of slightly less than half wavelength, the linear array achieve the best radiation, the directivity is the best. Under this spacing, the maximum gain can be increased by increasing the number of the elements, but there will be more sidelobes. Compared with linear array, the planar array compresses the main lobe width very much although get more side lobes in the plane perpendicular to the axial, and get a better directivity. Plane array brings problem that the mutual coupling become serious which brings the loss of efficiency. However, due to the narrow width of main lobe, improved directivity, the planar array is more suitable for the sensitive directional working environment.