Cover-Ended Resonators to Increase Corona Discharge Thresholds in Microstrip Bandpass Filters

In this work, corona discharge breakdown thresholds in microstrip bandpass filters are studied. If a gas is subjected to strong electric fields, gas breakdown may occur with severe consequences for microwave devices. The objective of this paper is to propose a solution for the mentioned problem for a microstrip bandpass filter, through the implementation of dielectric material covers over the open-circuit terminations of the resonators forming the filter, where the voltage magnification is maximum. A parametric study of covers' dimensions for an open-ended resonator is presented, and it is analyzed how the maximum electric field strength and the unloaded quality factor are affected. Finally, the aforementioned study is applied to the design of a fifth-order bandpass filter with hairpin resonator configuration centered at 1.6 GHz. Numerical results show that by using this strategy, the peak power handling capability (PPHC) of microstrip filters can be considerably enhanced without hardly degrading the filter response performance.