Research On The Impact Of Gtem Cell On Eut’s Radiation Characteristics And New Applications Of Gtem Cell

GTEM cell is a new electromagnetic compatibility test site which appeared in the end of1980s. Recently in some large-scale activities such as2008Olympic Games, GTEM cell is applied to the spot test with strong real-time ability because of its advantages:low cost、wide band and strong mobility and so on. More attentions are paid to it by testers. The range of its application is becoming larger and application area is extended constantly, for example EMC test、antenna gain test、electric field probe calibration and so on. The dissertation is based on National Nature Science Foundation of China under Grant60971069and it is centered on the relevant research projects of the founadtion. The name of the foundation is research on the impact of GTEM cell on EUT’s radiation characteristics and its compensation method. The main research of the dissertation contains two aspects:the impact of GTEM cell on some typical EUT’s radiation characteristics and new applications of GTEM cell. The dissertation not only establishes the base for futher improvement of EMI testing technique, but also furtherly expands application area of GTEM cell. The main purpose of this paper is promoting the theoretical research on the interplay between GTEM cell and EUT and pushing forward greater development of GTEM cell in practical test use.The main work and creative points of the dissertation:(1) The input impedance of symmetrical dipole antenna in GTEM cell is derived in this dissertation and compared with the input impedance of it in free space, the features of the change between them are obtained. The relationship of the change of input impedance with three parameters which are the length of antenna、the distance from the center of antenna to the septum of GTEM cell and the distance between the center of antenna and the port is mainly analyzed. The conclusions can give some guidelines to the EMI measurement in GTEM cell. This research establishes the base for further improvements of EMI measurement in GTEM cell and provides theoretical basis for test compensation.(2) HFSS electromagnetic simulation software based on FEM is employed to model and simulate GTEM cell and the reliability of the simulation is verified from theory and experiment aspects. Although some papers use different electromagnetic calculation methods like FDTD method、TLM method and so on to simulate GTEM cell, it is very difficult to duplicate them because we not only need deeply understand the theory of the methods, but also optimize simulation program. Some simulations even use realistic simulation to simulate the end of GTEM cell, and this costs lots of simulation time and affects simulation efficiency. The repeatability and efficiency of using HFSS software to simulate GTEM cell is very well. Besides the features of the change between the input impedance of ring antenna in GTEM cell and in free space are studied preliminarily through simulation.(3) The new method of using GTEM cell to measure RCS of electrically small scatterers is first put forward in detail. The well agreement between experiment results and theoretical results valids the reliability of it and it provides a new path for electromagnetic scattering measurement. Traditionally Compact Antenna Test Range and Outdoor Static Test Site are used to do electromagnetic scattering measurement, but the cost of the two sites is extremely high and the usable lowest frequency limit is tens of Megahertz or few hundred Megahertz. While the cost of GTEM cell is low, the volume of it is small, the usable frequency rang of it is from DC to several Gigahertz and the testing process of using GTEM cell to measure RCS is simpler and more convenient. The new test technique is with strong practicality and good application prospect. It not only can be applied to the measurement of the RCS of usual electrically small scatterers but also could be applied to the measurement of Delta RCS of UHF RFID passive tags. The well agreement between the test results of Delta RCS in GTEM cell and anechoic chamber reflects the practical value of this new test technique.(4) Give out the method of using GTEM cell to measure the axial ratio and gain of circularly polarized antenna and a new universal RFID reader antenna with UHF frequency band which is desiged in the dissertation is measured using this method. Compared with the test process in anechoic chamber, the method of using GTEM cell to do antenna measurement is simpler without standard reference antenna. It can show advantages especially in the measurement of wideband antenna.