A High-Power Widely Tunable Limiter Utilizing an Evanescent-Mode Cavity Resonator Loaded With a Gas Discharge Tube

A new plasma-based widely tunable power limiter is introduced and experimentally investigated in this paper. The proposed limiter is composed of a high- Q evanescent-mode cavity resonator loaded with a gas discharge tube in its gap area over the post. Increasing input power results in enhancing electric field over the gap, which eventually leads to microwave gas breakdown and plasma formation. The limiter loss after the breakdown depends on the electron density in the tube, which itself is a function of input power. Hence, the limiting mechanism is self-sustained. The threshold power is tunable either coarsely by selecting different tubes with various breakdown voltages or finely by dc biasing the tube. In a fabricated proof-of-concept limiter at 2.16 GHz with 22% bandwidth, preionization by an external dc bias provided 15.5 dB of limiting power tunability in the range of 370 mW-13 W, while the limiter could easily handle up to 100-W input power. The response time of this limiter is <;10 ns. Thanks to the nature of capacitively coupled microwave gas discharge in the α-discharge regime, the limiter performance is quite stable and no degradation was observed after a long operation under high input power.