Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-06-08
2001-12-11
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S212000, C333S230000
Reexamination Certificate
active
06329889
ABSTRACT:
TECHNOLOGICAL FIELD
The invention relates in general to electrical and mechanical constructions in high-frequency filters. Particularly the invention relates to the mechanical and electrical construction of a coupling element that can provide desired electromagnetic couplings between parts in a high-frequency filter.
BACKGROUND OF THE INVENTION
A high-frequency filter is a filter the operating frequency of which falls in the range of a few hundred megahertz to tens of gigahertz. Known high-frequency filters are based on a few known basic resonator types. Resonator types include the helix resonator, in which the inner conductor is a cylindrical coil conductor and the outer conductor an electrically conductive casing; the dielectric resonator, in which the inner conductor is the electrically conductive coating of a hole formed in the dielectric body block and the outer conductor is the coating on the outer surface of that same body block; and the coaxial resonator, in which the inner conductor is a straight conductor the cross section of which is constant or changes in a step-like manner at some points, and the outer conductor is an electrically conductive casing not unlike the one in the helix resonator. The filter types are called helix filters, dielectric filters or coaxial filters according to the resonator type used. The present invention is applicable to filters in which the resonators' outer conductor is the electrically conductive casing. Resonators are also called filter circuits, and each portion of the casing that includes the inner conductor of a resonator is called a compartment.
In known high-frequency filters, the desired zeroes in the filter's frequency response are realized by means of link chains. To adjust the coupling, specially designed coupling elements are needed. The couplings required for achieving the desired response may be capacitive or inductive in nature or they may have both capacitive and inductive characteristics. A disadvantage of the link chain is that when a portion of the chain is adjusted, the adjustment tends to have a considerable effect on inter-circuit couplings as well as on the frequency, bandwidth and other characteristics of the circuits. Therefore, it is very difficult to set the specifications for the link chain. Because of the nature of the coupling and the construction of the filter the electrical implementation and mechanical construction of the coupling elements are unique in each individual case and therefore the coupling elements are expensive and laborious to manufacture. In addition, the assembly process is hard to automate.
U.S. Pat. No. 5,608,363 discloses different coupling methods in a filter construction which comprises at least two parallel resonator rows. The frequency response zeroes in the filter are realized by means of coupling elements attached to the walls between the resonator cavities. Disadvantages of the coupling elements described in the patent include the need for an economical and reliable attachment method for the necessary insulating material and the coupling element proper.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a coupling element which can be applied to arrange inter-resonator couplings in a high-frequency filter and which has a simple construction and operation and is mechanically strong. Another object of the invention is to provide a coupling element which can be generally used especially in conjunction with filter constructions with thin walls. A further object of the invention is to provide a coupling element the manufacture and end use of which can be easily automated and are therefore economically advantageous.
The objects of the invention are achieved by a construction combining an electrically conductive element, which has specifications as desired, and insulating material separating said conductive element from the rest of the construction, which insulating material may at the same time serve as a connecting surface to connect the construction so as to become part of a filter.
The coupling element according to the invention is characterized in that it comprises
a first conductor which has a first end and second end,
an insulating part, such that
a portion of the first conductor located between the first end and second end of the first conductor is wholly surrounded by the insulating part,
on both sides of said portion the first conductor comprises a portion which is outside the insulating part,
the insulating part is arranged so as to become attached inside a high-frequency filter.
The invention also pertains to a high-frequency filter which comprises a first resonator and second resonator such that the first resonator has an inner conductor and the second resonator has an inner conductor and the inner conductors are surrounded by an electrically conductive casing comprised of compartments. It is characterized in that to provide electromagnetic couplings between resonators it comprises a coupling element which comprises
a first conductor which has a first end and second end,
an insulating part, such that
a portion of the first conductor located between the first end and second end of the first conductor is wholly surrounded by the insulating part,
on both sides of said portion the first conductor comprises a portion which is outside the insulating part,
the portion on a first side of said portion and outside the insulating part is located in the same casing compartment with the inner conductor of the first resonator, and the portion on a second side of said portion and outside the insulating part is located in the same casing compartment with the inner conductor of the second resonator.
The invention further pertains to a method for manufacturing a coupling element in a high-frequency filter. The method according to the invention is characterized in that it comprises steps in which
a portion between the ends of a conductor is surrounded with insulating material such that on both sides of said portion the conductor comprises a portion which is outside the insulating part
the entity comprised of the insulating material and conductor is placed inside an electrically conductive casing in a high-frequency filter, and
the entity comprised of the insulating material and conductor is attached to an inner surface of the casing.
The coupling element according to the invention has at least one electrically conductive part, or a conductor, and an insulating part which may at the same time serve as a connection surface to connect the construction so as to become part of a filter. A separate connection part may also be used. The insulating part is flat, i.e. it has in two perpendicular directions a dimension which is substantially greater than the dimension of the insulating part in a third direction which is perpendicular to the other two directions. The conductor or conductors are elongated and placed such that part of every conductor travels inside the insulating part and projects from the insulating part at a point which is intended to be located near a certain inner conductor of a resonator. Conductor parts traveling inside the insulating part are directed mainly to those directions in which the insulating part has a significant dimension.
The coupling element according to the invention is placed inside a filter casing such that the insulating part or a separate connection part if one is used, is positioned against a certain even surface of the casing. The surface in question is preferably the “top” or “bottom” of the casing, which terms refer to those surfaces of the casing that are perpendicular to the longitudinal axes of the inner conductors of the resonators. Then the conductor in the coupling element extends from a first compartment of the casing to a second compartment. If the coupling element has two conductors, the first of them extends from a first compartment of the casing to a second compartment, and the second extends from a third compartment to a fourth compartment such that said first compartment may be the same as the third compartment an
Darby & Darby
Filtronic LK Oy
Jones Stephen E.
Lee Benny
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