Wave transmission lines and networks – Resonators – Dielectric type
Reexamination Certificate
2000-01-21
2002-03-26
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Resonators
Dielectric type
C333S202000, C333S207000, C333S222000, C333S223000
Reexamination Certificate
active
06362707
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to filters and other devices utilizing dielectrically loaded resonators and more particularly to dielectrically loaded resonators with expanded tuning capabilities.
BACKGROUND ART
Resonators are commonly used in filters and other devices to receive and transmit electronic signals. Hollow metal resonators may be tuned to operate in a broad range of frequencies and bandwidths, however, their size and weight make them undesirable for use in many applications. It is known in the art that loading resonators with high dielectric constant ceramic materials can reduce the size and weight. The use of resonators with high dielectric constant ceramic materials can also reduce the size of filters by up to a factor of ten from the size of filters using hollow metal resonators. However, present dielectrically loaded resonators are limited in that they must be designed for a specific range of frequencies and bandwidths due to their limited tuning range.
In order to increase the range of frequencies and bandwidths in which these current resonators may be used, they may be subjected to tuning. Tuning present dielectrically loaded resonators beyond relatively minor adjustments, however, requires special manufacturing processes. These special manufacturing processes increase manufacturing schedules and the costs involved with manufacturing filters and other devices utilizing these resonators.
There are a variety of known configurations of dielectrically loaded resonator structures with three primary configurations. Some configurations require the resonators to be designed for a specific manufacturing use. Stocking multiple configurations for a broad range of applications is costly. Alternatively, modifying dielectric blanks for resonators or the filters that contain them involves relatively time consuming and expensive operations to achieve more than minor adjustment of their frequency range.
The first known example is composed of a high dielectric material plated on a metal resonator structure. This example does reduce the size and weight of the resonator, but it does so at the expense of tunability. Tuning of this configuration requires grinding the metal resonator structure to size and replating the high dielectric material coating. This is a difficult, costly and time-consuming process. The result is that resonators must be manufactured to tight tolerances and for specific applications. This not only effects the cost of the resonators but also increases the manufacturing schedule of the filter or other device in which the resonators will be used.
The second example consists of a shell made of a high dielectric material that surrounds a center metal resonator structure. This configuration is advantageous over the other known configurations since it allows for tuning of the resonator over a greater frequency range by machining the center post. Fine tuning is usually accomplished by electrical loading through the use of variable capacitors or external tuning stubs.
The final example, consists of un-plated dielectric resonators. These resonators rely on the high dielectric constant of the material to form a resonator. These resonators also have the disadvantage of a narrow tuning range. Although no plating is required, coarse tuning still requires a special manufacturing operation to regrind the ceramic dielectric material.
Conventional hollow metal resonators have the advantage of allowing the use of tuning screws for fine tuning. In dielectric resonators, such a tuning screw provides a much more limited tuning range because the E-M fields do not propagate very far beyond the high dielectric constant ceramic material.
Conventional hollow metal resonators are easily grouped together to form multiple resonator filters which use coupling probes and ports to carry the RI signal from one resonator to the other. The coupling ports can also be made adjustable through the use of tuning screws. In dielectric resonator filters, forming multiple resonator filters is much more difficult. Because the E-M fields do not propagate very far beyond the high dielectric constant material, setting the right coupling between resonators is very sensitive to dimensional tolerances. Also, connecting probes between inner posts requires drilled-out sections between the resonators and makes assembly difficult.
There is, therefore, a need for a resonator that utilizes the size and weight advantages of high dielectrically loaded resonators while retaining the broad range and ease of tuning and assembly characterized by hollow metal resonators.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a resonator for use in filters and other devices that reduces the size and weight of the filters and provides easy tunability and for wide adjustability of the filters. It is a further object of the present invention to provide a multi-resonator filter with easily adjustable resonator couplings which reduces the schedule and cost of filter production.
In accordance with the objects of the present invention, an improved multi-resonator filter is provided. The multi-resonator filter contains resonators made up of a center metal resonator element surrounded by a high dielectric constant element. The high dielectric constant element is removable to allow easy tuning of the metal resonator element. Coarse tuning is accomplished by removing the high dielectric constant element and trimming the length of the center metal resonator element. After course tuning, the high dielectric constant element is replaced and affixed to the metal resonator element to keep the filter stable under vibration. The resonator also contains a fine tuning screw seated above the metal resonator element. The fine tuning screw can be turned to adjust the tuning of the metal resonator element. The high dielectric constant element extends above the metal resonator element to surround the fine tuning screw. By surrounding the fine tuning screw with the high dielectric constant element, the fine tuning range of the resonator is increased because the E-M field propagates up through the extended dielectric material.
The high dielectric constant elements contain slots in their sides to allow removable high dielectric coupling bridges to connect resonator sections within the multi-resonator filter. These high dielectric bridges increase the coupling between dielectrically loaded resistors to provide high dielectric constant paths for the E-M field between resonators. The high dielectric coupling bridges are easily removable to allow adjustment of the resonator couplings. High dielectric coupling bridges may be removed and adjusted or replaced to change the coupling between resonator sections. After adjustment of the coupling between resonator sections, the removable high dielectric coupling bridges are affixed to the dielectrically loaded resonators to keep the filter stable under vibration.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.
REFERENCES:
patent: 4307357 (1981-12-01), Alm
patent: 5329687 (1994-07-01), Scott et al.
patent: 5495215 (1996-02-01), Newell et al.
patent: 5712606 (1998-01-01), Sarkka
patent: 5777534 (1998-07-01), Harrison
Gudmestad Terje
Hughes Electronics Corporation
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