Study on the Influence of Creep on RF Coaxial Switch in Accelerated Thermal Cycle Test

Radio frequency (RF) coaxial switches have the advantages of high transmission frequency and power capacity and are widely used in aerospace, communications, military, science, and medical fields. In accelerated thermal cycle (ATC) test, a permanent deformation or displacement occurs in the contact system of RF coaxial switch caused by creep and the RF performance downgrades with the thermal cycle times. In this paper, a 3-D finite-element model of an RF coaxial switch was first proposed. The power loss in the contact system when the switch transmits high frequency and power signals was divided into the conductor loss and the dielectric loss, which were calculated separately. It was noted that conductor loss was the main part of power loss. Then, the power loss in the contact system was considered as the heat source, and the steady-state temperature field of the whole switch was calculated with Ansoft HFSS and Workbench. The temperature rise in an RF coaxial switch was calculated and verified by experimental testing. In order to predict the reliability and working life of RF coaxial switch in ATC test, a creep constitutive equation based on the Coffin-Mason method that has three undetermined coefficients was built. According to ISO204:2009 (Metallic materials-Uniaxial creep testing in tension), the samples of beryllium bronze for creep testing were produced, and two groups of creep testing in the condition of different temperatures and stresses were carried out to obtain the undetermined coefficients. Finally, the stress-strain deformation of contact system with the thermal cycle times was calculated based on the creep constitutive equation. The model of contact system was rebuilt, and the influence of creep on RF coaxial switch in ATC test was investgated. The analysis methods and conclusions presented in this paper have important theoretical significance and practical value for improving the performance and reliability of RF coaxial switch products.