EM-Thermo-Mechanical Investigations on Pillbox RF Window for 5 kW S-Band Microwave Tubes

Abstract

This article presents the design of pill box-type RF window working at an operating frequency of 2.998-GHz for 5-kW high-power microwave tubes. Concave, convex, and dome-shaped dielectrics are considered for a study of proposed windows with CVD diamond, Alumina (99.5%), and glass as dielectric materials. The reflection and transmission characteristics of all the proposed windows are investigated. The return and insertion loss for concave CVD diamond are 49.15 dB, 0.026 dB and for concave Alumina (99.5%) are 46.2 dB, 0.018 dB. The relative permittivity of the material and the dielectric thickness affect the reflection characteristics. From the thermal study, the maximum temperatures are observed at the center of the dielectric, causing thermal stress and displacement. The temperature rises when the input power is increased from 5-kW to 50-kW. Compared to CVD diamond and Alumina (99.5%), glass material experiences higher temperature growth. The maximum temperatures at 5-kW average input power for CVD diamond, Alumina (99.5%), and glass are 25.5°C, 25.6°C, and 108°C, respectively. From mechanical analysis, the stress and displacement for concave and dome-shaped dielectrics are less compared to those of convex and conventional. Stress distributed widely at the periphery of the dielectric whereas displacement occurred more at the center. According to EM-thermo-mechanical simulations, the concave CVD diamond is suitable for window design with a 1.6 mm dielectric thickness.