Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-09-23
2001-05-29
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S219100, C333S212000, C333S230000
Reexamination Certificate
active
06239673
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of microwave filters. More particularly, the present invention relates to a dielectric resonator filter which can be used in microwave communication systems, for example, in cellular phone base stations, in the personal communication service (PCS) markets, and the like.
2. Discussion of the Related Art
In the microwave communications market, where the microwave frequency spectrum has become severely crowded and has been sub-divided into many different frequency bands, there is an increasing need for microwave filters to divide the microwave signals into these various frequency bands. Accordingly, various waveguide and resonator filters have been employed to perform band pass and band reject functions in order to divide up the frequency spectrum into these different frequency bands.
In the field of microwave dielectric resonator filters, it is known that a bandwidth of such a filter is a function of a resonant frequency of dielectric resonators, within the filter, and respective coupling coefficients between each of the dielectric resonators. Thus, typically to achieve a desired bandwidth, the dielectric resonators are longitudinally spaced, in a cascaded manner, in a waveguide so as to provide desired inter-resonator coupling factors. Since the bandwidth is a function of the inter-resonator coupling factor and the frequency of resonance of the dielectric resonator, varying the spacing between the dielectric resonators results in variations in the bandwidth about the center frequency of operation. Accordingly, the overall filter dimensions, in particular the filter length, typically must be varied in order to meet a center frequency and bandwidth requirement. Therefore, in order to divide the microwave communications band up into the many different frequency bands of operation, a multiplicity of filter dimensions must be employed. However, with advances in technology, increasingly remote locations for base stations where such filters are to be employed, and decreasing size requirements, non-uniform filter dimensions are no longer acceptable.
Additionally, in the microwave communications band where such filters are to be employed, it is increasingly becoming a requirement that the filter have a large attenuation factor at a certain frequency from a center frequency of operation of the filter. For example, requirements for attenuation of spurious signals and of signals not in the pass band of the filter are becoming more difficult to meet, thereby requiring an increased complexity in a design of the filter. However, the typical solutions to such requirements such as increasing the number of resonator elements within the filter, can no longer be employed given the reduced size requirements of the filter.
Accordingly, it is an object of the present invention to solve the above-described disadvantages and to provide an improved dielectric resonator filter having one or more of the advantages recited herein.
In particular, the present invention provides a method and an apparatus for providing a dielectric resonator filter with a fixed inter-resonator spacing which can be employed at different center frequencies of operation and for different operating bandwidths.
Additionally, the present invention provides an improved dielectric resonator filter which can provide and increase attenuation ratio at a frequency offset from the center frequency, as compared to a dielectric resonator filter having a same number of dielectric resonators.
Further, with the present invention there is provided an improved dielectric resonator filter which can be easily manufactured.
SUMMARY OF THE INVENTION
In one embodiment of the invention, a dielectric resonator filter includes a plurality of dielectric resonators respectively disposed in a plurality of dielectric resonator cavities. The plurality of dielectric resonator cavities are defined by a plurality of walls. For each electrically adjacent dielectric resonator cavity, a coupling device is provided in a common wall, between the electrically adjacent dielectric resonator cavities, for coupling an electromagnetic signal between the adjacent resonator cavities. In addition, a second wall of selected non-adjacent resonator cavities includes a cross-coupling device which provides cross-coupling of the electromagnetic field between respective dielectric resonators of the selected non-adjacent resonator cavities.
With this arrangement, the dielectric resonator filter includes both in-line coupling factors and cross-coupling factors so that the filter can meet both in-band and out-of-band electrical performance requirements.
In another embodiment of the present invention, a method and an apparatus for providing a bandpass filter that will meet both in-band and out-of-band electrical performance requirements includes providing a first bandpass filter which has a bandwidth substantially the same as the bandwidth requirement of the bandpass filter and also meets the in-band electrical performance requirements. In addition, a second bandpass filter is provided in series with the first bandpass filter. The second bandpass filter has a pass-band broader than the pass-band of the first bandpass filter, an in-band electrical performance that in combination with the in-band performance of the first bandpass filter meets the in-band bandpass filter requirements and an out-of-band electrical performance, when in combination with the out-of-band performance of the first bandpass filter, meets the out-of-band electrical performance requirements of the bandpass filter.
With this arrangement, the series combination of the first bandpass filter and the second bandpass filter meets both the in-band and out-of-band electrical performance requirements for the bandpass filter, which are not achieved with a single bandpass filter.
In still another embodiment of the present invention, a method of providing a dielectric resonator filter with desired in-line coupling, between respective resonators of electrically adjacent resonator cavities, as well as desired cross-coupling, between respective resonators of non-adjacent resonator cavities, is provided. The method includes determining desired values of in-line coupling factors between respective resonators of the electrically adjacent dielectric resonator cavities, as well as determining values of cross-coupling factors between respective resonators of non-adjacent resonator cavities. In addition, a value of Q external (Q
ex
) at an input and output port of the filter is determined. The value of Q
external
is realized at the input port and at the output port by varying one of a diameter of a conductive rod of an input/output coupling device or by varying a length of the conductive rod of the input/output coupling device. Once the value of Q
external
has been realized, the in-line coupling factors are realized by varying a coupling device between the respective resonators of the electrically adjacent resonator cavities, so that the desired coupling factor between the respective resonators is achieved. In addition, the desired cross-coupling factor, between respective resonators of the non-adjacent dielectric cavities is achieved by varying a cross-coupling device. The step of varying the coupling device or the cross-coupling device is then repeated for each additional resonator, of the plurality of dielectric resonators, for which in-line coupling or cross-coupling is to be provided.
With this arrangement, the dielectric resonator filter is provided with desired in-line coupling factors between respective dielectric resonators of electrically adjacent dielectric resonator cavities and desired cross-coupling reactances between respective dielectric resonators of at least two non-adjacent dielectric resonator cavities.
In yet another embodiment of the present invention, a method of joining a first and a second part together to create an electrical and mechanical bond between the two parts is provided. The method includes fabr
Bartley Lucy
Bartley Paul
Erlinger William G.
Wenzel Robert J.
Bartley Machines & Manufacturing
Jones Stephen E.
Lee Benny
Wolf Greenfield & Sacks P.C.
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