Abstract: Proposed are a resonator which can easily establish coupling with input/output means, an external circuit, etc., and a filter, duplexer and communication apparatus each having a wide-band frequency characteristic. Electrodes having polygonal openings defined therein are formed in both principal planes of a dielectric substrate such that the openings are positioned to face each other. The dielectric substrate is arranged with the aid of spacers between a metal-made upper conductor case and a lower conductor case having a shield conductor formed therein, the upper and lower conductor cases being positioned to face each other with gaps left relative to the dielectric substrate. Portions of the dielectric substrate between pairs of the openings facing to each other serve as resonance areas and are coupled respectively with input/output electrodes.

Abstract: 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.

Abstract: In a dielectric filter in which electrodes are formed on both principal planes of a dielectric plate while pairs of electrode non-formed portions having substantially the same shape are defined in the electrodes in opposing relation, areas positioned between the pairs of opposing electrode non-formed portions serve as resonance areas, coupling members are provided to be coupled with the resonance areas, and a cavity is provided to define a space surrounding the resonance areas and the coupling members, a signal is prevented from propagating in the parallel plate mode through a waveguide path formed between electrodes formed on both principal planes of the base plate serving as part of a cavity. Electrodes are formed on both principal planes of a dielectric plate (3) with pairs of electrode non-formed portions (4a, 4b, 4c, etc.) defined in the electrodes in opposing relation so that areas positioned between the electrode non-formed portions serve as resonance areas.

Abstract: A process for preparing a colorless rosin comprising a step for purifying a disproportionated rosin and hydrogenating the rosin. According to the process, a rosin having a color nearly equal to colorless and is excellent in various properties such as odorless at heating and stability is prepared.