Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1998-12-11
2001-09-25
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S202000, C333S209000, C333S232000
Reexamination Certificate
active
06294970
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priorities of German Patent Applications, Ser. Nos. 197 55 744.9, filed Dec. 16, 1998, and 198 32 804.4, filed Jul. 21, 1998, the subject matters of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates in general to a bandpass filter, and more particularly to a multi-resonator bandpass filter of a type having a series of waveguide resonators positioned along a common longitudinal axis so as to define at least a first resonator and a last resonator, with adjacent resonators being mechanically linked to one another by a common coupling plate of sheet metal which is formed with coupling slots for electrically connecting the resonators, wherein the first resonator and the last resonator are closed by end plates of sheet metal.
Bandpass filters of this type are generally known. They have the drawback that the connection and closure of the individual waveguides require complicated and expensive flange structures. This is especially disadvantageous when considering that these bandpass filters are used in (digital) televisions operating in normal TV bands (f<1 GHz), and thus are very bulky.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an improved bandpass filter, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved multi-resonator bandpass filter in which the resonators are connected to one another by a more cost-efficient construction compared to conventional designs.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a series of waveguide resonators formed from a longitudinally welded sheet metal and positioned along a common longitudinal axis, thereby defining opposite axial ends, with one end being closed by a first end plate of sheet metal and the other end being closed by a second end plate of sheet metal, wherein the first and second end plates and the common coupling plates between adjacent resonators are each formed with circumferentially spaced tabs which are bent so as to extend along the adjoining waveguide resonator, with the tabs being welded to the waveguide resonators, and with the joints between the first and second end plates and the common coupling plate, on the one hand, and the adjacent waveguide resonators, on the other hand, being soldered.
A bandpass filter according to the present invention can be manufactured in a cost-efficient manner while still being stable and exhibiting a low transition resistance between the individual waveguide resonators. The high stability is realized by welding the coupling plates between adjacent waveguide resonators and the end plates onto the respective waveguide resonators. The low transition resistance between individual waveguide resonators and the sheet metal plates (end plates and coupling plates) which extend transversely to the center axis of the filter is realized by soldering the joints between the plates and the respective waveguide resonators. Thus, the use of expensive flanges is eliminated. The same advantages are realized also for a dual mode bandpass filter which has only one resonator closed on opposite ends by two end plates but lacks the need for a coupling plate.
This technique is applicable in bandpass filters with waveguide resonators of random cross section, and can also be applied in bandpass filters with coaxial resonators.
According to another feature of the present invention, one of the waveguide resonators is formed with an input coupling terminal and another one of the waveguide resonators is formed with an output coupling terminal, whereby the input coupling and output coupling terminals are welded, preferably spot-welded, to the pertaining waveguide resonators, with the joints being soldered. In this manner, a cost-efficient and yet stable connection is effected.
Preferably, the common mechanical longitudinal axis of the resonators extends substantially vertical.
According to still another feature of the present invention, the filter can be so attached to a filter carrier that in a first mode of attachment the filter is securely fixed to the filter carrier, and in a second mode of attachment the filter is floatingly mounted to the filter carrier. In vertical alignment, the filter is subject to least tensions so that undesired deformations and detuning of the filter are prevented. This is further compounded by the floating mount of the filter to the filter carrier during operation. The floating mount of the filter substantially eliminates a possibility for deformation of the filter as a consequence of varying dilatations of the support structure and the filter. If securely fixed to the filter carrier, the filter could be subject to mechanical stress and deformation, when acted upon by high HF power and thereby heated, so that the filter and the support structure undergo different thermal expansion, ultimately resulting in a detuning of the filter. The fixed connection of the filter to the filter carrier is preferred, however, when transporting the filter.
Preferably, the filter is statically defined in connection with the filter carrier, whereby e.g. the waveguide of one of the resonators is formed about its circumference with spaced brackets, with each of the brackets being defined by a horizontal leg which is formed with a bore and so connectable to the filter carrier by a screw fastener that the screw fastener traverses a spacer. The spacer is formed on both sides with a projection so that its disposition can be reversed or inverted, whereby one of the projections is so dimensioned as to partially engage the bore of the leg, and the other projection is so dimensioned as to fully engage the bore. In this manner, the attachment of the filter can be easily switched from the fixed mode of attachment for transport to the operative mode in which the filter is floatingly mounted, and vice versa.
According to another feature of the present invention, the attachment of the filter to the filter carrier further includes a plurality of profiled rails which are mounted externally onto the waveguide resonators in parallel relationship to the center axis thereof for attachment of the mounting brackets to the waveguide resonators, whereby the profiled rails and the mounting brackets are placed into one-to-one correspondence. In this manner, the deformation of the filter can be further minimized. Moreover, the fairly high rigidity of the end plates and the coupling plates shows then its full effect as bending forces transmitted via the profiled rails are absorbed.
A frequency alignment of the filter may be realized by arranging adjustment slides in the coupling slots of the coupling plate, with each of the adjustment slides being formed as a carriage which is guided in the associated coupling slot and supports a jumper which contacts opposing slot edges, and by arranging rods in one-to-one correspondence with the adjustment slides for adjustment of the adjustment slides from outside, whereby the rods extend radially in parallel relationship to a plane defined by the coupling plate. In the event the rods are made of metal, the required screening to the outside is effected by resilient contact sleeves which are connected by soldering to the resonator wall.
Preferably, at least the waveguide resonators, each coupling plate and the end plates are made of a material with small thermal coefficient of expansion, for example, invar.
REFERENCES:
patent: 4028651 (1977-06-01), Leetma
patent: 4513264 (1985-04-01), Dorey et al.
patent: 4578658 (1986-03-01), Urien et al.
patent: 5841330 (1998-11-01), Wenzel et al.
patent: 5969585 (1999-10-01), Nishiyama et al.
Appel Werner
Lang Manfred
Pinzel Hans
Pitschi Franz
Feiereisen Henry M.
Jones Stephen E.
Pascal Robert
Spinner GmbH Elektrotechnische Fabrik
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