HIGH-Q TUNABLE MICROWAVE CAVITY RESONATORS AND FILTERS WITH SCALABLE MANUFACTURING TECHNOLOGIES FOR 5G COMMUNICATIONS
Creators: name: Sinanis, Michael Dimitri
Publisher: name: Purdue University Graduate School
Year: 2022
Subjects: Industrial engineering
Manufacturing processes and technologies (excl. textiles)
Microtechnology
Precision engineering
Additive manufacturing

description: Wireless communications and interconnected devices have become ubiquitous in our everyday life. As the rollout of the 5th generation (5G), wireless communication technology is well underway, the number of interconnected devices is increasing exponentially. Estimations for 2021 predicted that 1.5 billion smart devices would sell globally, representing a $53.45 billion market size by 2022. With the increase of communication channels and transmitted data within these networks, the challenge of coexistence without interference will become prominent. Simultaneously, 5G networks are introducing more frequency bands while densifying the network of communication towers. Forecasts predict a 100X increase of the network at the edge by introducing small cell towers, with projections estimating 45 million installed by 2031. As a result, rapid exponential growth in hardware costs is expected. Also, these dense networks will require a higher degree of self-configuration to prevent adjacent band interference. Tunable filters and large-scale manufacturing technologies are two solutions to address these challenges. Reconfigurable high-quality evanescent-mode (EVA) filters have been extensively presented in the literature. Different mechanisms have been employed for tuning, such as piezoelectric actuators and motors, and magnetostatic and electrostatic actuators. Furthermore, these implementations have been realized with printed circuit board (PCB) technology, computer numerical control (CNC) machining, 3D printing, and silicon (Si) micro-machining. Specifically, PCB manufacturing of three-dimensional front-end tunable filters has been promising and can deliver excellent performance. In addition, they can be integrated into the existing manufacturing lines and circuitry for the RF front-end. Nonetheless, there are limitations in fabrication tolerances that PCB manufacturing could reach. Consequently, there are restrictions on the frequency bands that these devices can be manufactured as dimensions become smaller in higher bands. Moreover, EVA cavities have been proven to yield higher performance filters when compared to unloaded quality factors and power handling of currently used substrate integrated waveguide (SIW) based technologies. Specifically, EVA filters produced with silicon micro-manufacturing combined with MEMS actuators have been demonstrated with remarkable performance up to 100s of GHz. Also, cost limitations per unit built are significant compared to other technologies like injection molding. The research goal of this work is to investigate scalable, low-cost manufacturing processes and techniques while maintaining a high-performance device. Combining knowledge from silicon RF MEMS tuned EVA filters and the cost-effective mass manufacturing injection molding technology to deliver a high-Q, high power handling, low-cost tunable filter. Demonstrating these characteristics within the same manufactured prototype would be a unique solution within the existing literature on tunable filters. This thesis is organized into three parts. The first part is focused on design for manufacturing (DFM). Si micromachining has been used to produce tunable resonators and filters at lower bands, but higher bands have yet to be demonstrated. The low-cost batch fabrication of already established Si micromachining lines makes this an attractive technology to realize these devices. This section presents network densification’s challenges and the economics of scale-up manufacturing. Furthermore, using Si micromachining, the first high Q tunable W band RF resonator is demonstrated tuned with MEMS technology. In the second part, the focus is on design for performance (DFP). Si micromachining is optimized to demonstrate high-performance RF MEMS tunable filters up to 100s GHz. High Q, wide tuning range, and low actuation voltages for the MEMS tuners have been realized. In the third part, the focus is on design for cost (DFC), where injection molding manufacturing technology is proven to have significant advantages in low cost with respect to other large-scale manufacturing technologies. A high-performance tunable resonator and filter in the sub-6 GHz frequency band are manufactured. They prove that simultaneously high Q, widely tunable, high power capable filters can be produced with low-cost scalable manufacturing technology.