Resonant modes in re-entrant cavities

Experimentally-determined tuning characteristics are presented for a long cylindrical re-entrant cavity having dimensions similar to those used for Gunn oscillators and for studies on semiconductors. The results indicate the simultaneous existence of the dominant TEM and the fundamental TE modes of resonance. A perturbation technique is given for the identification of the modes. Theoretical calculations of the resonant frequencies using simple models are presented. Experimental values of the Q-factors of the resonator for both the modes of resonance are also given.