High Q printed helical resonators and filters

High Q compact printed helical resonators are described operating around 1.8 to 2 GHz. These consist of a multilayer PCB incorporating a printed helical transmission line. Losses in the via holes are reduced by ensuring that the standing wave current at this point is near zero. This ensures a significant increase in Q (around 4x). Further increased energy storage per unit volume is achieved due to the 3D helical nature of the resonator. Unloaded Qs of 235 and 195 have been obtained on low loss PCBs with dielectric constants of 2.2 and 10.5 respectively. As a further demonstrator a three-section filter, designed to offer the response required by the front end filter of a modern GSM phone, has been developed.