Ka-band Cavity Filter Manufactured in 3D-printed Alumina Technology

This paper presents the design and the fabrication of a compact Ka-band dielectric cavity filter, manufactured in 3D-printed alumina technology. The goal is to achieve a flat in-band insertion loss, keeping constrained the device size. A 4th order and a 8 ^th order cavity filters with 4 transmission zeros were designed and tested. The 8 ^th order filter were designed using dual mode cavities in order to introduce additional transmission zeros without increasing the manufacturing complexity of the ceramic part. The filter is fabricated on low tanδ alumina which allows to achieve relatively high Q factor reducing the size of the device. The resonators exhibit a relatively- high unloaded Q-factor up to 800 which allows to increase the flatness in the operative bandwidth (27GHz-29.4GHz, FBW 8.5%). The selection of the material and filter geometry determine a very low occupation area (14×25mm ² ). The cavity filter has been mounted on alumina substrate to improve the thermal stability of the joint. The device demonstrates good robustness to thermal variations in the range between −10 and 70°C.