Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2000-02-15
2001-08-14
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S222000
Reexamination Certificate
active
06275125
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to wave filters, and deals more specifically with radio frequency filters of the kind comprising two or more coaxial dielectric resonators in juxtaposition. The radio frequency filters according to the invention find typical applications in mobile or portable telephone sets, although no unnecessary limitations thereto are intended.
Bandpass or bandstop radio frequency filters have been known which typically take the form of a pair of juxtaposed coaxial dielectric resonators operating in transverse electromagnetic (TEM) mode, as disclosed for example in U.S. Pat No. 5,578,975 to Kazama et al. Methods have also been known of capacitively coupling together the dielectric resonators One such known method, according to Japanese Unexamined Pat. PUb. No. 7-176911, teaches to provide layers of electrically conductive material on the opposed surfaces of the resonators, thereby obtaining capacitances between the conductive layers and the inner conductors of the resonators, and to solder or otherwise join the conductive layers. These conductive layers are referred to as resonator coupling conductors.
The dielectric resonators have been further provided with additional conductor layers on their outer surfaces for use as terminals in connecting the filter to external circuits. These terminals should of course be electrically isolated from each other as much as possible. Difficulties have been encountered, however, in realizing a desired degree of isolation between the terminals because they have been capacitively coupled together in devices composed of juxtapositions of two or more dielectric resonators.
Additional problems left unsolved with dielectric resonator wave filters arise from the present-day demand for smaller and smaller devices. The outer conductor of each resonator is provided with extensions to one end of the dielectric body according to one known downsizing method, and, according to another such method, the inner conductor is joined directly to a conductive layer, or inner conductor extension, formed on one end of the dielectric body.
Such known downsizing methods are alike in aiming at lower resonance frequencies with each dielectric body maintained at the same length as before. This objective, known as the wavelength shortening effect, is obtained as the capacitance between the extensions of the outer conductor and the inner conductor, or between the extension of the inner conductor and the outer conductor, of each resonator is connected in parallel with the resonance circuit of each resonator proper, resulting in a decrease in resonance frequency. For example, the resonance frequency of a device having a pair of dielectric resonators may decrease from 1900 megahertz, in the case where no such downsizing measures are taken, to as low as 1000 megahertz when the noted capacitance additionally connected in parallel with the resonance circuit of each resonator is 20 picofarads.
Let us now consider a wave filter comprised of juxtaposed dielectric resonators having the inner conductor extensions, the terminal conductors, and the resonator coupling conductor Capacitances between resonator coupling conductors and inner conductors and capacitances between terminal conductors and inner conductors change with the size of the inner conductor extensions. The aforesaid wavelength shortening effect is therefore not adjustable by the inner conductor extensions without affecting the capacitances in question.
The terminal conductors and the resonator coupling conductors have presented a further problem. These conductors have been required to be of not less than a certain size for providing the desired capacitances, running counter to the size reduction of the filters incorporating them.
A yet further problem with dielectric filters in general has been the spurious resonance at thrice the fundamental frequency or thereabouts. The spurious resonance has resulted in insufficient attenuation of that higher harmonic.
SUMMARY OF THE INVENTION
In view of the foregoing state of the art it Is among the objects of the present invention to improve lation between the terminal conductors in wave filters having two or more dielectric resonators in juxtaposition.
Another object of the invention is to make readily adjustable the wavelength shortening effect of wave filters of the kind defined, with little or no influence on capacitances between resonator coupling conductors and inner conductors or on capacitances between terminal conductors and inner conductors.
Yet another object of the invention is to reduce the sizes of the terminal conductors and the resonator coupling conductors in wave filters of the kind defined.
A further object of the invention is to overcome the spurious resonance that has heretofore occurred at about thrice the fundamental frequency in wave filters of the kind defined, and hence to make possible the attenuation of that harmonic frequency.
Briefly, the invention concerns a dielectric wave filter having at least two dielectric resonators in juxtaposition. Each dielectric resonator comprises a dielectric body having a plurality of side surfaces between a pair of opposite end surfaces, and a resonance hole extending between the pair of end surfaces. An inner conductor covers an inner surface of the dielectric body whereas an outer conductor covers those parts of the side surfaces of the dielectric body which are contiguous to one of the end surfaces of the dielectric body. The outer conductors on both dielectric bodies are joined to each other both mechanically and electrically. A shorting conductor covers said one end surface of the dielectric body and so electrically interconnects the inner and the outer conductors. Also formed on each dielectric body are a resonator coupling conductor covering part of at least that side surface of each dielectric body which confronts the other dielectric body, and a terminal conductor covering part of the side surfaces of each dielectric body and disposed adjacent the other of the end surfaces thereof. The resonator coupling conductors on both dielectric bodies are joined to each other both mechanically and electrically. The terminal conductors on both dielectric bodies are disposed at least on those side surfaces of the dielectric bodies which face away from each other. The invention particularly features an outer conductor extension extending from the outer conductor on each dielectric body toward said other end surface thereof, the outer conductor extensions on both dielectric bodies being disposed at least on those side surfaces of the dielectric bodies which confront each other, thereby intervening between the terminal conductors on both dielectric bodies.
Thus the terminal conductors of the two dielectric resonators are better isolated from each other than heretofore by the outer conductor extensions intervening therebetween. Experiment has proved that little or no signal leakage occurs from the input to the output terminal conductors in filters constructed according to this invention.
The outer conductor extensions on the dielectric bodies serve the additional purpose of providing the wavelength shortening effect by virtue of capacitances between them and the inner conductor The wavelength shortening effect makes it possible to provide smaller size filters.
According to a further feature of the present invention, the inner conductor of each resonator is also provided with an extension. Disposed on said other end surface of each dielectric body, the inner conductor extensions function to make the wavelength shortening effect even more pronounced.
According to a still further feature of this invention, the outer conductor extensions can be so patterned as to provide greater inductances for attenuating the third harmonic of the fundamental frequency.
The above and other objects, features and advantages of this invention and the manner of realizing them will become more apparent, and the invention itself will best be understood, from a study of the following description of s
Igarashi Masao
Inoue Makoto
Kosaka Takeshi
Sato Kazuhisa
Takei Kenji
Lee Benny
Summons Barbara
Taiyo Yuden Co. Ltd.
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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