1. Technical Field
The disclosure relates to cavity filters, and more particularly relates to a tuning structure of a cavity filter.
2. Description of Related Art
Cavity filters are popularly applied in mobile communications.
However, during adjustment of the resonating frequency of the cavity filter 10, metal shavings may be produced by the tuning posts 15, because the tuning posts 15 and the lid 12 are both metal. Such shavings can migrate to electronically sensitive areas of the cavity 100, with resulting intermodulation distortion (IMD) of the cavity filter 10.
Therefore, a need exists in the industry to overcome the described limitations.
It should be understood that although only two resonators 26 are shown for simplification and convenience of description, with a corresponding two threaded holes 30 and two tuning posts 28 shown, more than two resonators, posts, and holes may be used without departing from the spirit of the disclosure.
In the embodiment, each threaded hole 30 comprises a stopper portion 40 extending from an inner surface 31 thereof inward so as to form a step 41 defining a through hole 42 in communication with the threaded hole 30. In the embodiment, the through hole 42 receives the tuning rod 282 of the tuning post 28. During adjustment of the resonating frequency of the cavity filter 20, the threaded portion 281 is received in the threaded hole 30 and the tuning rod 282 traverses through the through hole 42. Accordingly, the step 41 of the stopper portion 40 is able to retain metal shavings produced when the resonating frequency of the cavity filter 20 is adjusted.
In the embodiment, an outer surface of the tuning rod 282 of each tuning post 28 fits substantially snug against an inner surface of the through hole 42, preventing metal shavings from entering the cavity 200.
Alternatively, the cavity filter 20 further comprises a plurality of sticky elements 50 each located on the step 41 of the stopper portion 40 of each threaded hole 30. During adjustment of the resonating frequency of the cavity filter 20, the metal shavings cannot enter the cavity 200 because they are stuck to the sticky elements 50. Because the stopper portions 40 are weak electric field areas of the cavity filter 20, the metal shavings collected there do not influence performance of the cavity filter 20, with resulting improvement of intermodulation distortion (IMD) of the cavity filter 20, and increased stability of the cavity filter 20. In addition, the stoppers 40 may also prevent the tuning posts 28 from falling into the cavity 200, which also lowers ratio of operation defect.
While the exemplary embodiments have been described, it should be understood that it has been presented by way of example only and not by way of limitation. The breadth and scope of the disclosure should not be limited by the described exemplary embodiments, but only in accordance with the following claims and their equivalent.
Number | Date | Country | Kind |
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200920314693.6 | Nov 2009 | CN | national |