A Narrowband 3-D Printed Invar Spherical Dual-Mode Filter With High Thermal Stability for OMUXs
Lu Qian, Yi Wang, Sheng Li, Abd El-Moez A. Mohamed, Moataz M. Attallah, Talal Skaik, Paul Booth, Laurent Pambaguian, César Miquel España, Petronilo Martín-Iglesias
Abstract
A 3-D printed narrowband bandpass filter based on spherical dual-mode resonators is presented in this article. It is designed for output multiplexers (OMUXs) using high-<inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> spherical dual-mode resonators. Realization is by laser powder bed fusion (L-PBF) technology of Invar alloy chosen for its low coefficient of thermal expansion (CTE). Using PBF circumvents the alloy’s manufacturability issues associated with its hardness in machining and free forming. Compared with polymer-based vat photopolymerization technology, PBF allows for direct metal manufacture of complex monolithic microwave components with better thermal-mechanical properties and higher power-handling capability. Using Invar can further help achieve high temperature stability of the filter in high-power operation. To demonstrate the proposed solution, detailed thermal-RF test at different temperatures was carried out. The experimental results of a 0.47% fourth-order silver-plated Invar filter with two transmission zeros verify the design and manufacturing. An insertion loss of 1 dB and an effective temperature coefficient of less than 2 ppm/K were achieved.