Patent Publication Number: US-11036022-B2

Title: Hollow waveguide termination device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 10 2012 015 578.6, filed Aug. 8, 2012, the disclosure of which is expressly incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hollow waveguide termination device that utilizes a waveguide termination housing and an inner attenuation element arranged therein and made of a material which absorbs electromagnetic oscillations. 
     2. Discussion of Background Information 
     Hollow waveguides are waveguides for electromagnetic waves that propagate at a frequency in the frequency range of approximately 1 GHz to over 300 GHz. These hollow waveguides, which are typically formed from metal tubes of a differing cross section, are suitable for transmitting waves of frequencies that are this high with low loss. In particular, hollow waveguides of this type are used in radar devices, microwave devices or high-frequency radio units. They are also used in space engineering. 
     In order to avoid the energy transported in the hollow waveguide being radiated off into the free space at the end of the tubular hollow waveguide, the hollow waveguide must, at the free end, be provided with a termination device functioning as effective resistance. A hollow waveguide termination is a wave pool that serves to cancel the wave energy in the hollow waveguide system. The incident energy is further transmitted with low reflection into the hollow waveguide termination and thereby dissipated to the metal housing as heat in the lossy, oscillation-absorbing material. 
     Termination devices of this type are known. On the Internet page http://www.radartutorial.eu/17.bauteile/bt42.de.html (accessed on Apr. 10, 2012), for example, a hollow waveguide termination is shown and described. In this example, the hollow waveguide piece is several wavelengths long and filled with graphite-coated sand. This graphite-coated sand forms an attenuation element which is arranged distributed in the inside of the hollow waveguide termination in a cascading or pyramidal manner and incrementally reduces the inner cross section of the hollow waveguide. In such a pyramidal attenuation element, the base of the pyramid is connected to the front face of the hollow waveguide, but normally covers only a small part of the surface of the front face, and has no contact whatsoever with the side walls of the hollow waveguide. This hollow waveguide termination, which must be several wavelengths long due to its design, is not suitable for certain applications in which it is necessary to perform construction in a space-saving manner, for example, in satellite engineering, because of its longitudinal extension. 
     U.S. Pat. No. 7,868,714 B1, the disclosure of which is hereby incorporated by reference in its entirety, discloses a compact hollow waveguide termination in which the inner circumference of a hollow waveguide is provided with an oscillation-attenuating material in the region of its free end. For this hollow waveguide termination, the complete reflection at the end of the hollow waveguide is used in order to achieve the double losses, as the wave reflected by the end of the hollow waveguide is likewise attenuated by the attenuation material provided on the inner circumference. In this known hollow waveguide termination, the axial extension of the attenuating material is also extended at the inner circumference to improve the attenuation, whereby the dimensions of the hollow waveguide termination increase. 
     SUMMARY OF THE INVENTION 
     The invention encompasses a generic hollow waveguide termination device such that an improvement of the attenuation properties is achieved at a reduced overall length. 
     This can be attained via a hollow waveguide termination device having one or more features shown in the drawing and/or described herein. 
     In one non-limiting example, the attenuation element has a cup shaped configuration as well as a tubular section. A front wall section closes off the tubular section on one side. 
     The provision of an attenuation element having a cup shape of this type, in which attenuation element both the annular circumference and the front-face terminal wall have oscillation-absorbing material, makes it possible to achieve a more pronounced attenuation of the wave energy without the length of the attenuation element having to become greater thereby. The portions of a wave further transmitted by the inner circumferential wall of the tubular section and not absorbed are further attenuated on the front wall and, from there, only that portion of the wave which has not been absorbed by the front wall is still reflected. This re-reflected remainder in turn encounters the tubular section and is once again attenuated there. In comparison with the known hollow waveguide terminating devices, a higher attenuation is achieved at the same effective length of the attenuation element or the overall length of the attenuation element, and therefore of the hollow waveguide terminating device, is reduced at the same attenuation according to the invention. 
     In addition, the mechanical stability of the attenuation element is markedly improved over the prior art as a result of the cup-shaped embodiment of the attenuation element with a tubular section and a front-face wall section closing the tubular section on one side. 
     The embodiment of the attenuation element with a front wall section furthermore increases the outer contact surface of the attenuation element, by way of which the attenuation element bears against the hollow waveguide termination housing surrounding it, whereby the conduction of heat from the attenuation element into the hollow waveguide termination housing is improved over the prior art. 
     Furthermore, the embodiment of the attenuation element according to the invention is tolerant with respect to a potential inhomogeneity of the oscillation-absorbing material. The hollow waveguide termination device according to the invention is also suitable for the attenuation of a broadband frequency spectrum. 
     The inventive concept is thus to use the face in addition to the inner circumferential surface for the attenuation of the oscillation, on the one hand to achieve an additional attenuation of the wave, but on the other hand to also ensure an extremely stable mechanical design which can be manufactured in a simple and repeatable manner despite the hardness and brittleness of the oscillation-absorbing material. 
     The principle of operation of the hollow waveguide termination device according to the invention is improved over the prior art in that the wave portions that have not been completely absorbed by the tubular section of the attenuation element and are further transmitted by it impinge on the front face of the attenuation element, which is likewise formed from oscillation-absorbing material. Here, these wave portions are further attenuated and, in case wave portions that are reflected on the front face of the attenuating element should still remain, then these wave portions would once again encounter the tubular part of the attenuation element and are re-attenuated here. 
     An advantageous development of the hollow waveguide termination device according to the invention is characterized in that the hollow waveguide termination housing has a cover element that is provided with an opening, which is preferably embodied as a blind hole, and in that the cup-shaped attenuation element is inserted in the opening of the cover element. This design allows the hollow waveguide termination device to be assembled in a simple manner and also creates a flexibility such that different attenuation elements can be inserted in the cover element. 
     It is thereby advantageous if the hollow waveguide termination housing has an inlet element which is embodied for mounting on the cover element and which is provided with a pass-though opening that is flush with the opening of the cover element when the inlet element is mounted on the cover element. The provision of such an inlet element makes it possible to provide, per hollow waveguide band, a standard cover element that accommodates the cup-shaped attenuation element and to perform the adaptation to various sub-bands by means of the inlet element, which then forms an adapter element. 
     It is furthermore advantageous if the pass-though opening of the inlet element has on its front face facing the cover element a step extending the free cross section and if the free end of the tubular section of the attenuation element inserted in the cover element is embodied to engage with the step in the pass-through opening such that the step hinders the attenuation element from falling out of the opening of the cover element when the inlet element is mounted on the cover element. In this manner, the attenuation element in the hollow waveguide termination housing utilizes a cover element and an inlet element that is captively retained in the opening of the cover part. 
     In another advantageous embodiment of the hollow waveguide termination device according to the present invention, the free cross section of the pass-through opening is larger than the free cross section bounded by the tubular section such that a step is formed by a part of the face at the free end of the tubular section at the transition from the pass-through opening to the attenuation element. This step preferably extends along the entire circumference of the pass-through opening, preferably without interruption. This adapter step is a combination of the cross section of the hollow waveguide inlet element and the inner and outer cross section of the front wall of the tubular part of the attenuation element. This step forms an adapter step for adapting the incident energy to the attenuation element. 
     Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
       The sole FIGURE shows a partially cut perspective representation of a hollow waveguide termination device according to one non-limiting embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice. 
     In the sole FIGURE there is shown a hollow waveguide termination device according to the invention that utilizes a hollow waveguide termination housing  1  and an inner attenuation element  2  arranged therein. 
     The tube waveguide termination housing  1  includes a cover element  10  and an inlet element  14 , which can essentially have the same cross section dimensions but may have different thicknesses. In the example shown, element  10  is thicker than element  14 . The cover element  10  and the inlet element  14  are connected to one another by fasteners such as screws  11  and these are screwed into threaded openings in the cover element  10  from the side of the inlet element  14 . The head of each screw  11  is countersunk in an enlarged bore of the inlet element  14 . 
     On a side facing the inlet element  14 , the cover element  10  is provided with an opening  12  having the form of a blind hole. Alignment pin bores  13  are provided in the cover element  10  and are, in the assembled state shown, flush with alignment pin bores  13 ′ of the inlet element  14 . These alignment pin bores  13 ,  13 ′ serve to accommodate alignment pins (not shown), that are used to ensure a precise reciprocal positioning of cover element  10  and inlet element  14 . 
     The inlet element  14  is provided with a central pass-through opening  16  that is flush with the opening  12  of the cover element  10  when the inlet element  14  is mounted on the cover element  10 . The pass-through opening  16  in the input element  14  widens toward the cover element  10  and/or includes an expanded section  16 ′ and a circumferential step  15 . The face of the step  15  faces the cover element  10 . 
     On the face  14 ′ of the inlet element  14  facing away from the cover element  10 , there are arranged outer centering strips  17  projecting from the face  14 ′. These are arranged along the outer edge. An inner center strip  17 ′ likewise projects from the face  14 ′ of the inlet element  14  and surrounds the pass-through opening  16 . In this example, the opening  16  has a rectangular shape with rounded-off corners (as seen in cross section). The inner centering strip  17 ′ surrounding the pass-through opening  16  is interrupted at least by one groove  17 ″, which is provided on the longitudinal or longer side of the inner centering strip  17 ′. 
     The cup-shaped attenuation element  2  is inserted into the opening  12  of the cover element  10 . This opening  12  is embodied as a blind hole. The attenuation element  2 , which is made of an oscillation-absorbing material, has a tubular section  20  and a front wall section  22  that closes off the tubular section  20  on one of its sides. In embodiments, element  2  is preferably embodied as a one piece member with both the wall  22  and the tubular section  20  being portions of the same member. The tubular section  20  has a rectangular cross section with rounded-off corners. The length of the attenuation element  2  (measured in a direction at a right angle to the front wall section  22 ) is greater than the depth of the blind hole bore  12  such that the tubular section  20  projects with its free end  20 ′ from the face of the cover element  10  facing the inlet element  14 . The outer dimensions of the tubular section  20  of the attenuation element  2  are dimensioned such that the free end  20 ′ of the tubular section  20  engages properly in the expanded section  16 ′ of the pass-through opening  16  in the inlet element  14 . In the assembled state of the hollow waveguide termination device illustrated, the front face  20 ″ of the tubular section  20  bears against or contacts the step  15  of the pass-through opening  16 . 
     The thickness of the wall of the tubular section  20  of the attenuation element  2  is, at least in the region of the front face  20 ″ thereof, greater than the extension of the step  15  measured at a right angle to the axis of the pass-through opening  16 , such that the free cross section at the free end  20 ′ of the tubular section  20  is smaller than the free cross section of the pass-through opening  16 . This results, in the assembled state illustrated, in the tubular section  20  of the attenuation element  2  in turn forming a step  24  which runs along the circumference of the pass-through opening  16  and the face of which faces away from the cover element  10 . 
     The attenuation element  2 , which is loosely inserted in the blind hole opening  12  of the cover part  10  during assembly, is fixed in a mechanically captive or retained manner in the hollow waveguide termination device by way of the step  15  of the pass-through opening  16 . The front wall section  22  of the attenuation element  2  and parts of the tubular section  20  are, as a result, placed in planar contact with the cover element  10  and inlet element  14 . Elements  10  and  14  are components that can be made of metal, preferably of a suitably heat-conducting light metal (for example, aluminum), such that the heat produced in the attenuation element  2  during the attenuation of high-energy electromagnetic oscillations can be quickly and effectively dissipated to the cover element  10  and the inlet element  14 . 
     The hollow waveguide termination device according to the illustrated invention is connected to the free end of a hollow waveguide such that the free end of the hollow waveguide either engages in the pass-through opening  16  or bears flush against the inner centering strip  17 ′. The electromagnetic oscillations emerging from the hollow waveguide then enter the pass-through opening  16  of the hollow waveguide termination device according to the invention, and this pass-through opening forms a hollow waveguide inlet. These electromagnetic oscillations are then attenuated on the inner wall of the tubular section  20  and the front wall section  22  of the attenuation element  2 . 
     The energy incident at the hollow waveguide inlet is in large part further transmitted into the attenuation element  2 , which forms a cup absorber, and is attenuated there. However, a part of the incident electromagnetic oscillation is reflected at the step  24  formed by a part of the front face  20 ″. The attenuation in the attenuation element  2  and the geometry of the attenuation element  2 , in particular, the inner length of the tubular section  20  (measured in the direction of the axis of the pass-through opening  16 ), is designed such that a returning wave is produced by reflection on the inside of the front wall section  22 , the amplitude of which returning wave is equal to the amplitude of the wave reflected at the step  24 . The phase of which is however shifted 180° such that this returning wave cancels the wave reflected at the step  24 . A cancellation of energy thus results at the inlet by way of the destructive interference of the reflected energy from the front wall section  22  of the attenuation element  2 . 
     Although the cross section of the pass-through opening  16  and the cross section of the tubular part  22  of the attenuation element  2  is shown and described as having a generally rectangular shape with rounded-off corners, both the cross section of the pass-through opening  16  and the cross section of the tubular part  22  of the attenuation element  2  (and therefore also the cross sections of the attenuation element  2  and of the blind hole opening  12 ) can have any other conceivable shape. Thus, these cross sections can, for example, include shapes such as cylindrical, half-cylindrically, square, etc. 
     It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.