A vertically integrated tunable UHF filter

A novel, vertically integrated filter design is used to produce a tunable UHF filter in a polymer based substrate. The filter is a sub band of a widely tunable narrowband preselect filter array and makes use of unused substrate space within the array to increase the overall tuning range of the array while keeping the substrate volume constant. This paper will discuss the use of mixed three dimensional electromagnetic and SPICE simulation in the design of the tunable filter. The fabrication of the filter using standard PCB fabrication techniques will be described and measured performance of the filter will be compared to the simulated response. High inductor and capacitor Q's were required to meet insertion loss specifications over the entire tuning range of the filter. The design and simulation of vertically integrated coupled parallel plate inductors and the careful design of the combination of static capacitors and tuning varactors to achieve the desired tuning and filter response will be highlighted.