Study On Microwave Automatic Test System Based On LabVIEW

As the microwave technology changes with each passing day, the research and measurement of the dielectric property has been an important part of modern science and technology. And it has been widely applied to many fields, such as:sources of energy, communication, bio-medical and electronics. Among them, the study of complex permittivity of the medium test appears particularly important. At the same time, with the development and progress of computer technology, automatic measurement is often used in Microwave test, automatic testing complex permittivity is necessary.The complex permittivity test method introduced in this article is different from the common ones. Here we use overmoded test method to measure complex permittivity. It is not only beneficial to observe the dielectric properties of materials at high frequencies but also convenient to process and analyses its data. Based on the laboratory existed conditions, the rectangular cavity perturbation method is applied to test complex dielectric constant. At the same time, we use electromagnetic simulation software HFSS to select the overmoded in 0～3 GHz band model. Through the model analysis, we finally determine the mode to test. Then we deduce the complex permittivity test formula with the method of rectangular cavity perturbation, and give the test parameters needed in actual tests. Based on LabVIEW2012 we completed the programming of automatic test software, so it can efficiently control AV3620A vector network analyzer test. In order to verify the correctness and stability of the test system, we test the dielectric constant of Teflon, Plexiglas and Nylon. Test results indicate that it is stable and has higher precision. Accompanied by the emergence of nanometer materials, accurate measurement of a batch of new microwave absorbing materials are going in-depth. In this paper, we mix carbon nanotubes with liquid paraffin in indefinite proportion by weight. This way improves the mixing uniformity. It reduces the error in the process of sample preparation, and increases the accuracy of the data. We test the dielectric properties of carbon nanotubes/paraffin mixture with the automatic test system. The results show that it has good potter absorption.Finally the paper presents the complex permittivity of nonstandard sample data modification; it is based on the HFSS simulation software. Combined with the simulation method, we can find that its value has a little error to the standard sample data. So in the case of non-standard measurement, it can be used as reference of its dielectric properties.