A new cylindrical cavity mode filtering method with broadband reversed-phase structure

Aim. The TE01p mode cylindrical cavity has very high quality factor (Q-factor), but its use on the broadband is not satisfactory because of the existence of disturbing mode. A new structure for filtering out disturbing mode is presented in some detail in the paper; microwave signal is divided into two parts completely reversed in phase and fed into a cavity; with the help of a part of helical waveguide, this structure obtains the purified TE01p mode in the whole working band. In this abstract, the following two topics are explained: (1) the principles of mode filtering, and (2) the measurement of the broadband reversed-phase structure. Topic 1 describes the method for restraining circumferential disturbing mode, which cannot be eliminated by the helical waveguide. In topic 2, the reflection coefficient and Q-factor of a cylindrical resonator with the new structure are measured. The measurement results and their comparison with other conventional structures, given in Figs.3 and 4 and Table 1, indicate preliminarily that the new structure effectively filters out all the disturbing modes except TE01p working mode and that the values of Q-factor measured for the new structure and other conventional structures are in good agreement.