High Power Limits of Waveguide Stub Tuners

Three effects limiting power handling capacity of a 2.45-GHz R-26 waveguide stub tuner have been investigated by means of electromagnetic simulation and partly by experiments: electric breakdown, microwave power dissipation in tuning stubs, and leakage of microwave radiation to environment. Critical situation in terms of load reflection coefficient has been identified. A tuner working chart is proposed which, for a given stub design, relates the highest tolerable microwave power for arc-free operation to maximum allowable load reflection coefficient. It is shown that high-reflection loads can increase noncontacting stub leakage levels by more than 10 dB, which should be considered in choke design. The described methodology can be applied to any type of waveguide and tuning stub structure.