Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2001-04-19
2004-07-13
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S219100, C333S230000
Reexamination Certificate
active
06762658
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a dielectric filter used in radio communications, and the like at high frequency band as microwave band; quasi-microwave band, and the like and a dielectric resonator used in the dielectric filter, and more particularly to a triple mode dielectric resonator in which three resonant modes are available in one dielectric block and a dielectric filter using the dielectric resonator therein.
TECHNICAL BACKGROUND
Conventionally, a dielectric filter which providing a cut-off waveguide with cylindrical or rectangular parallelopiped dielectrics disposing successively therein and utilizing resonance of a cylindrical TE01 &dgr; mode or a rectangular TE11 &dgr; mode of dielectrics is utilized widely in filters requiring low loss and size reduction, because the dielectric filter has high unloaded Q and can be reduced in size easier than waveguide type filter (a first conventional example). A resonance of the mode is generated by an electric field repeating reflections at an interface surface of the dielectric resonator and the air. The resonant frequency of dielectric resonator is inversely proportional to the length of the resonator and square root of dielectric constant, so that the larger the dielectric constant is, the smaller the resonator is. And a magnetic field generated by the resonance excites a resonator on the next stage and the excitation corresponds to the coupling between stages of the dielectric filter. As a magnitude of the coupling is mainly determined by the distance between resonators, the farther the distance is, the weaker the coupling is. As adjusting means for the above-mentioned dielectric filter, a method of adjusting the resonant frequency by a screw in a direction orthogonal to the reflecting surface of the magnetic field or a method of adjusting the coupling between the resonators by a screw, and the like are adoptable.
And there is also a dielectric filter utilizing a dual mode dielectric resonator in order to achieve size reduction (a second conventional example). The above-mentioned dielectric resonator provides two resonance by one resonator, in which a cylindrical dielectric resonator is disposed in the center of a cylindrical waveguide by justifying the axes of the cylinders, for example, and two resonance (HE11 &dgr;) generated in two directions orthogonal to the axes of the cylinders are coupled by disturbing the electromagnetic field of the resonance from the waveguide side using means as screws, and the like.
As the description about a first conventional example above, the resonant frequency of the resonator by a cylindrical TE01 &dgr; mode or a rectangular TE11 &dgr; mode of dielectrics depends on dielectric constant and the size of dielectrics and a resonator can be smaller when the dielectric constant gets larger, accordingly the simplest method of reducing size of the filter utilizing the dielectric resonator is to raise the dielectric constant of dielectrics.
However, as dielectrics with low dielectric loss used in microwave region generally has a characteristic that dielectric loss thereof increases as dielectric constant becomes higher, size reduction of the filter maintaining insertion loss low has a certain limitation. Further, as dielectrics with low loss as mentioned above is expensive, accordingly the filter becomes expensive when the filter provides more stages, that is, provides more dielectrics used therein.
And a filter relative to a second conventional example utilizing HE11 &dgr; dual mode dielectric resonator for size reduction has a problem that lots of undesired modes excited in the vicinity of pass band result in spurious characteristic deteriorated easily, because HE11 &dgr; is not the dominant mode.
On the other hand, for example, in the event that a dielectric filter used in microwave communications, and the like is composed, it is conventionally hard to reduce size and weight of a dielectric filter, because many resonators and each spaces between the resonators occupies large amount of volume and weight according to the requirement of one resonator for one resonance and space for coupling between each resonator. Therefore, there still is a problem that the dielectric filter is unavoidably composed complicated and large, even though it is a band pass filter using dielectric resonators of relatively small size.
Consequently, composing a dielectric filter using dielectric resonators capable of multiple mode resonance is proposed to realize a band pass filter with a very small and simple composition exploiting advantages in using dielectric resonators fully. For example, size reduction of a band pass filter having a double-tuned band characteristic by varying the resonant frequency of the two resonance modes to each other is proposed in unexamined Japanese Patent Publication No. Hei 7-58516, in which degenerate coupling of two resonance modes with respect to TE101 and TE01 &dgr; modes is disclosed (a third conventional example). And a multiple mode dielectric resonator capable of generating TM01 &dgr; mode and TE01 &dgr; mode which are generated on a surface parallel to each surface (x-y surface, y-z surface, x-z surface) in a rectangular coordinate system in a generally rectangular parallelopiped shaped dielectric block is proposed in unexamined Japanese Patent Publication No. Hei 11-145704 (a fourth conventional example).
However, it is still unavoidable that a dielectric resonator occupies a large amount of volume in a band pass filter requiring a resonator of multiple stages, even though the degenerate coupling of two resonance modes relative to the above-mentioned third conventional example as described in unexamined Japanese Patent Publication No. Hei 7-58516 is utilized. And even a triple mode dielectric resonator relative to the fourth example as described in unexamined Japanese Patent Publication No. Hei 11-145704 has a problem that the manufacturing process becomes complicated, because utilization of hybrid coupling of TM01 &dgr; mode and TE01 &dgr; mode which are orthogonal spatially requires the thickness of dielectric resonator to be adjusted to resonant frequency.
It is therefore a first object of the present invention to realize a dielectric filter capable of reducing the number of dielectric resonators to a large extent, aiming at size reduction and cost reduction and providing favorable out-of-band characteristic by incorporating the mode which has been undesired into the band and activating the mode as a portion of resonance necessary for filter characteristic exploiting advantages that unloaded Q of the dielectric filter by a cylindrical TE01 &dgr; ode or a rectangular TE11 &dgr; mode relative to a first and a second conventional examples is high.
And a second object of the present invention is to solve the problem of the above-mentioned third and fourth conventional examples and to provide a very small dielectric resonator with simple composition in spite of enabling a triple mode resonance and a dielectric filter using the above-mentioned dielectric resonator.
DISCLOSURE OF THE INVENTION
The present invention aims at size reduction of dielectric filter by using three resonant modes in one dielectric block in order to achieve a first object of the above-mentioned present invention. That is, in a block of a generally rectangular parallelopiped consisting of dielectric material, three resonant modes in a single dielectric block can be coupled by chamfering a ridge portion of the dielectric block and another ridge portion unparallel thereto.
That is, the dielectric resonator claimed in claim
1
is characterized in combining three resonant modes of the above-mentioned dielectric block by removing one ridge portion and another ridge portion unparallel thereto in a block of a generally rectangular parallelopiped.
It is apparent from physical symmetry characteristics that a rectangular TE11 &dgr; mode can exist in each of three orthogonal axial direction in a block of a generally rectangular parallelopiped. In a conventional dielectric filter using TE11 &dgr; mode or
Furuta Atsushi
Hwang Jae-Ho
Isomura Akihiro
McGinn & Gibb PLLC
Pascal Robert
Takaoka Dean
Tokin Corporation
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