Research On W-band Quasi-optical Cavity Technology

With the rapid development of modern microwave electronic system,it is urgent to develop and test high-performance microwave materials capable of working in W-band.Among them,the development and testing of W-band low-loss microwave dielectric material is the whole W-band microwave The foundation of technological development.For W-band low-loss microwave dielectric materials,it is very important to accurately measure the relative dielectric constant and loss tangent.In many W-band low-loss microwave dielectric materials,W-band quasi-optical cavity test method has high accuracy,The ability to suppress the mold,and easy to operate.It is very suitable for measuring the relative dielectric constant and loss tangent of the low loss microwave dielectric material in the millimeter wave band.In order to reduce or even eliminate the influence of high-order mode and improve the measurement accuracy,this paper studies the W-band quasi-optical cavity complex permittivity test system from the following aspects:1,It is easier to obtain the fixed cavity length method with high precision.By comparing the advantages and disadvantages of the flat cavity and the double cavity,the simple cavity structure is more convenient and the structure is easier to be loaded.2,According to the beam field theory,the internal field structure of the optical cavity is analyzed,and the electric field and magnetic field distribution of the Gaussian beam in the cavity are obtained by MATLAB numerical calculation.The basic parameters of the quasi-optical cavity and the derivation of the coupling coefficient ? are given.To study their effects on cavity performance.3,According to the basic parameters of the quasi-optical cavity and the coupling coefficient ?,the proper cavity length D is calculated by the exhaustive method.The HFSS electromagnetic simulation software is used for modeling and simulation.The performance of the quasi-optical cavity is analyzed and compared.The reflection frequency of the main mode and the higher order mode is compared with the theoretical calculation result,and the fundamental mode frequency deviation is less than 1MHz,which meets the test requirements.4,The design and mapping of the whole system are designed by using Solidworks three-dimensional mechanical structure design software.In particular,the tolerances of key dimensions and the shape and tolerances of the model are designed in detail.Finally,spherical mirrors,plane mirrors,Transfer board,mirror positioning device and other high column and other system-wide structural parts.5,Two sets of W-band quasi-optical cavity complex permittivity test system with different cavity length D were set up.The operating frequency was set between 86 GHz and 102 GHz,and the complex permittivity of the same quartz glass substrate sample was tested.The test results are compared with the theoretical results.