A resonator cavity for supporting a plurality of resonant modes and filtering electromagnetic energy, said resonator cavity comprising: (a) a cavity defined by a top end wall, a bottom end wall and a cylindrical sidewall, said cavity having a longitudinal axis along which the length of the cavity is defined; (b) a resonator element having: (i) a generally cylindrical rod defined by a top end and a bottom end, said generally cylindrical rod positioned within the cavity along the longitudinal axis of the cavity along which the length of the resonator element is also defined; and (ii) a mounting flange coupled around the generally cylindrical rod at the bottom end of the generally cylindrical rod and coupled to the bottom end wall of the cavity, wherein a complete bottom surface of the resonator element, including a bottom surface of the generally cylindrical rod and a bottom surface of the mounting flange, is coupled to the bottom end wall of the cavity to provide a thermal path between the resonator element and the cavity for heat dissipation; and characterized in that the cavity and the resonator element have dimensions selected so that the electromagnetic energy associated with the resonator cavity is defined by an electromagnetic feld pattern that substantially repeats itself at least twice along the length of the resonator element. (a) a cavity defined by a top end wall, a bottom end wall and a cylindrical sidewall, said cavity having a longitudinal axis along which the length of the cavity is defined; (b) a resonator element having: (i) a generally cylindrical rod defined by a top end and a bottom end, said generally cylindrical rod positioned within the cavity along the longitudinal axis of the cavity along which the length of the resonator element is also defined; and (ii) a mounting flange coupled around the generally cylindrical rod at the bottom end of the generally cylindrical rod and coupled to the bottom end wall of the cavity, wherein a complete bottom surface of the resonator element, including a bottom surface of the generally cylindrical rod and a bottom surface of the mounting flange, is coupled to the bottom end wall of the cavity to provide a thermal path between the resonator element and the cavity for heat dissipation; and characterized in that the cavity and the resonator element have dimensions selected so that the electromagnetic energy associated with the resonator cavity is defined by an electromagnetic feld pattern that substantially repeats itself at least twice along the length of the resonator element. (i) a generally cylindrical rod defined by a top end and a bottom end, said generally cylindrical rod positioned within the cavity along the longitudinal axis of the cavity along which the length of the resonator element is also defined; and (ii) a mounting flange coupled around the generally cylindrical rod at the bottom end of the generally cylindrical rod and coupled to the bottom end wall of the cavity, wherein a complete bottom surface of the resonator element, including a bottom surface of the generally cylindrical rod and a bottom surface of the mounting flange, is coupled to the bottom end wall of the cavity to provide a thermal path between the resonator element and the cavity for heat dissipation; and characterized in that the cavity and the resonator element have dimensions selected so that the electromagnetic energy associated with the resonator cavity is defined by an electromagnetic feld pattern that substantially repeats itself at least twice along the length of the resonator element.