High Gain Radio Frequency Antenna Technology Based On Metamaterials

Metamaterials attract extensive attention due to their special electromagnetic properties after being presented. And a large deal of research has been done by many scholars in electromagnetic field which mainly focuses on three-dimensional block metamaterials with complex structures. But it is hard to realize the conformal design for these materials to be used in the antenna design. The metasurface has made it possible. Metasurface, as an extension and expansion of metamaterials, is a two-dimensional thin layer made of metamaterials unit arranged as array structure. This kind of unit structure in specific combinations can realize the control and modulation of the electromagnetic wave reflection / transmission phase, polarization, propagation mode and so on. The characteristics of the antenna can be improved by loading the metasurface with different properties.RFID, as a currently widely used automatic identification technology, requires the reader antenna having the properties of wide bandwidth, circular polarization and high gain. And the common used antenna which always has some shortages limits the use of RFID. The RFID technology working at 5.8GHz frequency band is extensively used in electronic toll collection systems, storage and logistic system, etc because of its properties of low background noise and high efficiency of data transmission. However, the antenna working at 5.8GHz band have some problems, like large size, narrow circular polarization bandwidth, low gain and complicated structure.This paper carries out a thoroughly research on metasurface based on the basic theory and the dispersion diagram. In this paper, the metasurface was applied to microstrip slot antenna to make it wideband and circular polarized with the characteristics of high gain and low profile at the same time. The main works and innovations are as follows:Firstly, this paper analyzes a typical metasurface unit by using the transmission line model and the cavity model theory, and verifies the correctness of the simulation model by comparing different dispersion curves of theoretical values and simulation values. Besides, specific metasurface unit structural parameters of 5.8GHz get obtained through simulation s.Secondly, this paper analyzes the wideband mechanism of the microstrip slot antenna loaded with metasurface by studying the field distribution between the ground plane and the metal patch. Under the guidance of this theory, the wideband performance of the slot antenna gets achieved, the gain gets increased and the pattern gets improved. The correctness of the theory is further verified by the fabricated prototype.Thirdly, in this paper two polarization converting metasurface were proposed based on the theory that two orthogonal linearly polarized wave can generate circularly polarized wave. At the same time, the feasibility of polarization conversion by those two kinds of metasurface was analysed by the equivalent circuit theory.Fourthly, two kinds of wideband circularly polarized antennas based on microstrip slot antenna were successfully designed through applying the mechanism mentioned above. And these two antennas have the characteristics of high gain and low profile. A comparison of the simulation and experiment for the designed microstrip slot antenna loaded with angle-cut metasurface was carried out. Impedance bandwidth of measurement is 4.7~6.5GHz, relative bandwidth reached 32% and the simulation relative bandwidth is 38%. The AR bandwidth of measurement is 5.3~6.5GHz, relative AR bandwidth reached 20% and the simulation bandwidth is 20.8%.Through the above researches, this paper designed the microstrip slot antenna loaded with metasurface. The proposed antenna can not only achieve the broadband and circular polarization performance, but also own low profile, high gain and simple processing characteristics. The researches in this paper provide some new ideas and methods in the design of wideband circular polarization antenna. The designed antennas can find good applications in the wireless local area network, broadband wireless access system, automatic identification system and ETC.