Self-Temperature-Compensated Air-Filled Substrate-Integrated Waveguide Cavities and Filters

In this paper, patent pending self-temperature-compensated air-filled substrate-integrated waveguide (AFSIW) cavities and filters are proposed and demonstrated for high-performance and low-cost components, circuits, and systems on substrate. First, a theoretical multiphysics transmission line model is developed for the synthesis of self-temperature-compensated air-filled cavities. It is determined that temperature compensation can be achieved using an appropriate substrate material and dielectric sidewall slab width. Moreover, a postprocess temperature compensation technique is introduced to counterbalance potential fabrication errors. For demonstration purposes, a self-temperature-compensated first-order AFSIW filter (based on a single cavity) is fabricated and compared to its dielectric-less temperature-uncompensated counterpart. Then, a self-temperature-compensated fourth-order AFSIW filter centered at 21 GHz with 300-MHz bandwidth is designed and fabricated. It achieves a measured unloaded Q -factor of 975 at ambient temperature and a measured central frequency thermal stability as low as 2.26 ppm/°C at −40 °C and 1.67 ppm/°C at 80 °C (without using any postprocess tuning), compared to −17.4 ppm/°C at −40 °C and −18.38 ppm/°C at 80 °C for its dielectric-less temperature-uncompensated counterpart.