Theoretical and Experimental Study on Transient Electrical Behavior of Coaxial Bandpass Filter With Low-Pressure Microwave Breakdown

Gas ionization causing low-pressure discharge is a major limitation for the performance of microwave components. Simple structures such as coaxial, waveguide, and resonators have been relatively easier to predict the low-pressure discharge effect compared to complex microwave components, which remain challenging to accurately anticipate. There is still insufficient systematic research on transient response in this context. Consequently, analyzing the transient electrical behavior becomes essential when examining the mechanism of an electronic system’s response to gas discharge in an avalanche-like manner. This article aims to present a quantitative method revealing the relationship between microwave breakdown and system response in a fourth-order bandpass coaxial cavity filter. Initially, the inside field simulation is utilized to predict the microwave breakdown position in the filter. Additionally, the gas ignition transient process is simulated through the Monte-Carlo method, while considering electron–surface interaction and gas ionization. The experiments were conducted over a pressure range of 100–1000 Pa. It was observed that the breakdown phenomenon occurred in the input resonant cavity as predicted by the simulation, and the measured breakdown power threshold characteristic was consistent with the theoretical simulation. Furthermore, by utilizing the forward and reverse power cancellation signals, the transient impedance change upon breakdown was obtained without the use of any probes. It was revealed that the electrical behavior of the ionized gas, plasma, shifted from a capacitive load to an inductive load with an increase in gas pressure. The measured transient impedance characteristics showed a convex curve as the gas pressure increased, while the breakdown power threshold curve of the filter displayed a concave shape. This work verified an accurate simulation approach for predicting the ionization breakdown power for complex components and proposed an effective quantitative assessment method for the transient impedance change of the system response after breakdown occurs.