High-Q High Power Tunable Filters Manufactured With Injection Molding Technology

This paper presents the first demonstration of injection molding technology to enable large-scale mass manufacturing of high-performance tunable microwave filters to meet the growing needs of 5G small cell stations. This is the first time that a tunable filter satisfies all four of the following requirements simultaneously: low manufacturing cost, high quality factor, wide tuning range, and high power handling. Exhaustive research exists on the use of polymers for 3D microwave device manufacturing; nonetheless, mass-production technologies, such as injection molding, can provide low costs without compromising performance. The proposed bandpass filter implementation uses a tunable evanescent-mode cavity resonator injection molded with an acrylonitrile-butadiene-styrene thermoplastic polymer. In addition, changing the critical gap size over the resonator’s post using a commercial microactuator provides frequency tuning. The measured filter achieves an 86% tuning range from 2.8 – 5.2 GHz with a state-of-the-art measured unloaded quality factor $Q_{u}$ of 1548 – 2573. The filter has a measured insertion loss of 0.06 - 0.1 dB with a fractional bandwidth from 7.6 - 8.4% across the entire tuning range. Moreover, for the first time in this manufacturing technology implementation, a bandpass filter is demonstrated with power handling capabilities beyond 100 W. The manufactured device demonstrates the significant potential of this technology for the scale-up manufacturing of reconfigurable high- $Q$ RF filters without compromising the performance.