Exciting traveling waves in high Q structures using microstrip

Exciting traveling waves in high-Q resonant structures can simplify low noise oscillator designs and also has applications for newly proposed Lorentz invariance tests. In this work we use microstrip probes to excite traveling waves in a sapphire dielectric resonator. Previous work has indicated that matching microstrip probes to a sapphire resonator can be a difficult requirement. A model has been developed, which takes into account leakage of the microstrip line in the reverse direction to which we excite the traveling wave. From such a model we can define the standing wave ratio (SWR). By comparing the model with experiment we find that we can excite a traveling wave with an SWR of 0.35 and an unloaded Q-factor of 1.5×105 in a WGH12,0,2 mode at 9.997 GHz, in a sapphire cylinder of 5 cm diameter and 3 cm height. From the model, we also propose new oscillator designs for low noise applications.