Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-02-10
2001-05-15
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S202000, C333S222000
Reexamination Certificate
active
06232851
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a structures for filters, and more particularly to a structure for coupling cavity resonators within a filter.
BACKGROUND
Radio frequency (RF) equipment uses a variety of approaches and structures for receiving and transmitting radio waves in selected frequency bands. Typically, filtering structures are used to maintain proper communication using frequencies assigned to a particular band. The type of filtering structure used often depends upon the intended use and the specifications for the radio equipment. For example, bandpass filters formed with cavity resonators are often used for filtering electromagnetic energy in certain frequency bands, such as those used for cellular and PCS communications. A bandpass filter allows only a predetermined band of frequencies to pass through a signal path.
Many cellular telephone applications require the filter to have a very low insertion loss such as 0.5 dB within a bandwidth such as 840 MHz to 870 MHz. Such a low insertion loss requires the use of cavity resonators that have a very high Q or quality factor. Q provides a figure of merit for a resonator system. However, such a filter requires relatively large cavities, which creates a relatively large distance between resonators positioned in adjacent cavities. The difficulty is that increasing the distance between adjacent resonators reduces the coupling between them and causes inefficient bandwidth.
Another problem relates to the effects of temperature on the resonate frequency of the filter and hence on the performance of the filter. As the temperature of the resonator increase or decrease, they will expand or contract accordingly, which will change the resonate frequency of the resonators. Such a change in the resonate frequency may effect the passband of the filter and the integrity of the signal being passed through the filter.
Accordingly, there is a need for a mechanism to provide an adequate amount of coupling between adjacent resonators. There is also a need for a cavity resonator that has a mechanism for improving bandwidth characteristics. There is a further need for an improved cavity resonator that filters out the
3
d
harmonic from a signal. There is yet a further need for a cavity resonator filter that compensates for the effect of temperature changes. There is a related need for a filter structure that has minimal changes in the resonate frequency due to temperature changes.
SUMMARY
One embodiment of the present invention is directed to a resonator filter. The resonator filter comprises a housing formed with a conductive material. The housing defines a first cavity, a second cavity, and an intermediate wall positioned between the first and second cavities. The housing defines an opening between the first and second cavities. First and second center conductors are positioned within the first and second cavities, respectively. A coupler is connected between the first center conductor and the housing.
An alternative embodiment of the present invention is directed to a resonator filter having a housing formed with a conductive material. The housing defines a first cavity, a second cavity, and an intermediate wall positioned between the first and second cavities. The housing defines an opening between the first and second cavities. First and second center conductors are positioned within the first and second cavities, respectively. A coupling wire is connected between the first center conductor and the housing. The coupling wire and the center conductor have substantially equal thermal expansion coefficients.
An alternative embodiment of the present invention is directed to a resonator filter having a housing formed with a conductive material. The housing defines a first cavity, a second cavity, and an intermediate wall positioned between the first and second cavities. The housing defines an opening between the first and second cavities. First and second center conductors are positioned within the first and second cavities, respectively. A coupling wire is connected between the first center conductor and the housing. At least some of the same material used to form the coupling wire being the same as at least some of the material used to form the center conductor.
REFERENCES:
patent: 3008103 (1961-11-01), Maurer et al.
patent: 4280113 (1981-07-01), Sekiguchi
patent: 5446729 (1995-08-01), Jachowski
patent: 5684438 (1997-11-01), Cavalieri D'Oro et al.
patent: 273227 (1951-05-01), None
patent: 56 834 (1967-07-01), None
patent: 0 324 453 A2 (1989-07-01), None
patent: 0 324 453 A3 (1989-07-01), None
patent: 1 338 742 (1973-11-01), None
ADC Solitra Inc.
Fogg David N.
Fogg Slifer & Polglaze, P.A.
Nguyen Patricia T.
Pascal Robert
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