Adjustable resonator filter

{
  "publication_number": "US2006071737A1",
  "country": "US",
  "kind": "A1",
  "title": "Adjustable resonator filter",
  "abstract": "An adjustable resonator filter (200), the operating band of which can be shifted by a one-time adjustment. The natural frequency of each resonator (210, 220) is affected, in addition to the basic tuning arrangement, by an adjustment circuit (ACI), which includes a fixed tuning element (280) in the resonator cavity and an adjusting part (290) outside the cavity. The tuning element has an electromagnetic coupling to the basic structure of the resonator. The adjustment circuit is functionally a short transmission line, which is “seen” by the resonator as a reactance of a certain value. By changing the electric length of the transmission line, the value of the reactance and the electric length and natural frequency of the whole resonator are changed. The change is implemented in the adjustment part by means of switches or a movable dielectric piece. In the resonator filter each resonator has a similar adjustment circuit, and the adjustment circuits have common control (CNT) for shifting the band of the filter. When the subband division is in use, the filters need not be separately adjusted for each subband in connection with the manufacture. No moving parts are required inside the filter housing.",
  "claims": [
    "1. An adjustable resonator filter, which comprises a unity, conductive housing to form resonator cavities and an arrangement to shift an operating band of the filter by a one-time adjustment, wherein said arrangement comprises in each resonator an adjustment circuit with a fixed tuning element being located in the resonator cavity and having an electromagnetic coupling to basic structure of the resonator, and an adjusting part being located outside said housing, the tuning element and the adjusting part together with the resonator wall, which belongs to the housing forming a transmission line the electric length of which can be changed by means of a control of the adjustment circuit to change the natural frequency of the resonator, and said control is common for all the resonators of the filter in order to implement said one-time adjustment in shifting the operating band of the filter.",
    "2. A filter according to claim 1, the tuning element being galvanically insulated from the conductive walls bounding the resonator cavity.",
    "3. A filter according to claim 1, the tuning element being in galvanic contact with conductive bottom of the resonator.",
    "4. A filter according to claim 1, wherein the adjusting part comprises a conductor pattern between a first point connected to the tuning element and second point and switches, and said control has been arranged to affect these switches to change the length of the conductor between the first and the second point in order to change the electric length of said transmission line.",
    "5. A filter according to claim 1, wherein the adjusting part comprises a dielectric adjusting piece and a rigid conductor connected to the tuning element, a straight portion of which conductor runs through the adjusting piece, and said control has been arranged to affect the adjusting piece in order to slide it along the rigid conductor to change the electric length of said transmission line.",
    "6. A filter according to claim 1, the adjusting part being covered by a protective sheet to shield the adjustment circuit against external interference fields and to prevent the adjusting part from radiating to the environment.",
    "7. A filter according to claim 1, the resonators of which being quarter-wave coaxial resonators.",
    "8. A filter according to claim 1, the resonators of which being half-wave dielectric cavity resonators.",
    "9. A filter according to claim 4, the adjusting part comprising a circuit board, to which said conductor pattern and switches belong.",
    "10. A filter according to claim 4, said switches being of the MEMS type.",
    "11. A filter according to claim 5, wherein, in order to implement said common control, the dielectric adjusting pieces of the resonators have been mechanically connected to each other by means of a control rod outside the filter housing.",
    "12. A filter according to claim 11, said control rod being arranged to be moved electrically by means of an actuator."
  ],
  "description_excerpt": "The invention relates to a filter consisting of resonators, the operating band of which can be shifted by a one-time adjustment. A typical application of the invention is an antenna filter of a base station.\n\nWhen a resonator filter is manufactured, its transmission characteristics, i.e. its frequency response, must be arranged to comply with the requirements. This requires that the strengths of the couplings between the resonators are correct and that the resonance frequency, or natural frequency, of each resonator has a pre-determined value especially in relation to the natural frequencies of other resonators. In serial production, the variation of the natural frequency of a certain resonator of different filters is generally too wide with regard to the filter requirements. Because of this, each resonator in each filter must be tuned individually. Tuning like this is here called the basic tuning. A very common resonator type in filters is a coaxial quarter-wave resonator, which is shorted at its lower end and open at its upper end. In that case the basic tuning can be performed, for example, by turning the tuning screws on the cover of the filter housing at the inner conductors of the resonators or by bending the protruding parts of the extensions formed at the ends of the inner conductors. In both cases, the capacitance between the inner conductor and the cover changes in each resonator, in which case the electric length and natural frequency of the resonator also change.",
  "cpc": [
    "H01P 7/10",
    "H01P 1/2053",
    "H01P 7/04"
  ],
  "ipc": [
    "H01P 1/203",
    "H01P 1/20",
    "H01P 1/202",
    "H01P 1/205",
    "H01P 1/207",
    "H01P 1/208",
    "H01P 7/04",
    "H01P 7/10",
    "H01P 1/201"
  ],
  "assignees": [
    "Filtronic Comtek Oy"
  ],
  "inventors": [
    "Jukka Puoskari"
  ],
  "filing_date": "2005-10-31",
  "publication_date": "2006-04-06",
  "priority_date": "2004-06-08",
  "application_number": "US-26447905-A",
  "family_id": "32524465",
  "cited_by_count": 5,
  "citations": [
    "US3703689A",
    "US3876963A",
    "US4080601A",
    "US4186359A",
    "US5184096A",
    "US5949302A",
    "US5677654A"
  ]
}