The invention provides a dielectric resonator for example in the TE010 mode characterized in that electrodes are formed on both principal surfaces of a dielectric plate in such a manner that influence of spurious waves propagating in a space between the electrodes and a conductive plate is prevented thus preventing the reduction in Qo and degradation in the attenuation characteristic in the frequency ranges outside the passband. The inner diameter of the cavity is selected such that when the cavity is regarded as a waveguide the cutoff frequency of the waveguide becomes higher than the resonant frequency of a resonance region and such that the inner diameter of the cavity is greater than a non-electrode part.

A dielectric resonator loaded cavity filter comprises a housing having an exterior and an interior, the housing interior including at least two adjacent cavities having dielectric resonators mounted therein. The adjacent cavities are separated by a transverse partition having a coupling window therein, the coupling window having first and second spaced opposing sidewalls. In one embodiment a coupling disk is interposed between opposing sidewalls of the transverse partition. In another embodiment a coupling strip extends from a shoulder portion of a first opposing sidewall toward a shoulder portion of a second opposing sidewall.

A filtering system with a probe for coupling two resonators includes an iris having the probe disposed therein coupled between the two resonators. The probe has a transverse opening for receiving a tuning conductor, and the tuning conductor provides adjustable coupling between the two resonators.

A filter apparatus includes an enclosure defining a plurality of cavities. A pair of resonators are located in a corresponding pair of the cavities. The filter apparatus further includes an elongated coupling structure operatively interposed between the pair of resonators. The elongated coupling structure is spaced from each of those resonators uniformly along its length.

A composite resonator (10) consisting of a conducting metal (14) and a dielectric material (12) is used to provide resonant frequencies lower than can be obtained using the same volume of dielectric alone and with higher unloaded Q than can be obtained using the same volume of metal imbedded into a cavity and used as a resonator. This significantly reduces the cost and size of the resonator (10) without degrading its performance. An inexpensive metal (14), such as aluminum, can be substituted for more than half of the dielectric (12) and stille form a resonator (10) with substantially equivalent resonant properties. The operative embodiments of the resonator invention (1) cover composites with doughnut-shaped, i.e., cylindrical, configurations, with the "doughnut" either metal (14) or dielectric (12), and the "hole" either dielectric (314) or metal (312), respectively.