Metallized plastic surface-mount cavity resonators and filters

A novel method for the design and fabrication of low-cost filtering devices for cellular applications is presented in this paper. The proposed filter technology is based on the integration of 3-D coaxial resonators with 2-D printed-circuit boards (PCBs). Specifically, metallized plastic resonators are properly mounted on planar PCBs, while printed transmission lines (i.e. striplines) are employed to feed and couple the resonators. In this approach, high-Q resonators are integrated with conventional planar transmission lines, allowing for the design of filters that exhibit satisfactory performance (small in-band insertion loss, good close-to-band selectivity) while remaining light in weight, slim in volume, low-cost and compatible with standard PCB technology. The critical design parameters of the proposed class of resonators and filters, together with simulations and measurements of such filters are reported in the text, while the technical difficulties encountered during the fabrication of the filters are discussed.