Tuning fork filter design for hand scribe tuning

This paper proposes a design technique for high-performance planar filters. The technique provides tuning elements that enable filter tuning by hand scribing, and a parameter extraction based technique to determine what should be scribed. Each resonator has a tuning element, the tuning fork that provides shunt capacitance to ground and is coupled to the resonator by means of a series capacitor. The resonator is tuned by physically disconnecting part of the shunt capacitor. The series capacitor reduces the tuning sensitivity to approximately 10% of what would be seen if the tuning fork was directly connected to the resonator. This reduced sensitivity enables tuning by hand, e.g. with a diamond scribe. A parameter extraction based technique was developed to diagnose the filter couplings and resonant frequencies, and to provide a recipe for scribing the tuning forks. As an example a 10-pole high temperature superconducting filter was designed, fabricated, and scribed. The predicted and measured results agree very well for this filter.