Hollow waveguide device

Abstract

A hollow waveguide device (1) for radio frequency electromagnetic waves comprises sa cavity (6) that extends in one direction of propagation (7) of the electromagnetic waves. The cavity (6) is enclosed by metallic inner walls of the hollow waveguide device (1). The hollow waveguide device (1) comprises a channel body (2) with at least one channel recess (8) that extends in the direction of propagation (7) and that is accessible from a channel surface (9) of the channel body (2). The hollow waveguide device (1) further comprises a lid body (3) that is mounted onto the channel surface (9) of the channel body (2) and that covers the at least one channel recess (8) to form the electromagnetic wave conducting cavity (6) of the hollow waveguide (1). The lid body (3) is bonded onto the channel body (2) by means of a contact layer (11) that is arranged between the lid body (3) and the channel surface (9) of the channel body (2). The contact layer (11) is made of a dielectric adhesive material and that completely encloses the at least one channel recess (8) in the channel surface (9).

Description

Technical Field

[0001] The invention relates to a hollow waveguide device for radio frequency electromagnetic waves with a cavity that extends in one direction of propagation of the electromagnetic waves, whereby a largest diameter of a cross-sectional surface of the cavity perpendicular to the direction of propagation is less than the extension in the direction of propagation, whereby the cavity is enclosed by metallic inner walls of the hollow waveguide device, whereby the hollow waveguide device comprises a channel body with at least one channel recess that extends in the direction of propagation and that is accessible from a channel surface of the channel body, and that further comprises a lid body that is mounted onto the channel surface of the channel body and that covers the at least one channel recess to form the electromagnetic wave conducting cavity of the hollow waveguide. The invention also relates to a method for manufacturing such a hollow waveguide device.State of the Art

[0002] In the field of radio frequency signal transmission, the manufacturing of complex shaped hollow waveguide units methods can be challenging. Usually, common manufacturing techniques involve extrusion, CNC machining and injection moulding. With extrusion methods, it is possible to manufacture a straight line hollow waveguide section as one piece. However, such straight line hollow waveguide sections do not allow for variations in shape or cross-section. With the exception of such straight line hollow waveguide sections, most manufacturing methods typically necessitate dividing the waveguide block into a minimum of two parts to facilitate the manufacturing process.

[0003] It is well known in prior art to manufacture a channel body with at least one channel recess that extends in a direction of propagation as one-piece made of metal, to manufacture a lid body by the same or similar manufacturing methods, and to mount the lid body onto the channel body in a manner that prevents any gap along a contact line between the channel body and the lid body that surrounds a channel recess, as any gap between the metal bodies allows for unwanted leakage of radio frequency electromagnetic waves, resulting in a significant weakening of the electromagnetic wave signal that is transmitted along the hollow waveguide device.

[0004] In high microwave frequencies, particularly for wavelengths of electromagnetic waves in the range of millimetres, effectively managing and minimizing leakage of electromagnetic waves through gaps within metallic inner walls or other openings is considered critical, but challenging. Achieving radio frequency transmission without power leakage usually necessitates securing the split parts with screws, i.e. mounting and fixing the lid body onto the channel body by a number of screws that are arranged along a contact line around the channel recess that forms the cavity. The quantity of screws that is needed depends on the flatness of the surfaces, the operating frequency, and the location of the separation plane. The use of screw mount clamping is a widely recognized and economical technique for assembling waveguides comprising two or multiple parts.

[0005] Mounting split parts with screw fasteners imposes significant constraints on the design, usually necessitating a bulky structure, dedicated space for the arrangement of screws around each channel recess, and specific wall thicknesses of the channel body and the lid body along the contact line to be able to absorb the forces for the required contact pressure that is exerted by the screw connection. This limitation not only hampers design flexibility but also adds significant weight to the hollow waveguides, rendering them more expensive. In addition, the required screwing operations also slowdown the assembly process which usually adds significant cost especially when mass produced parts are to be assembled.

[0006] Moreover, even when the channel body and the lid body are screw-mounted, the location of the gap and its axis with respect to the direction of propagation may introduce some leakage, whereby the risk of leakage increases at high frequencies. Therefore, unless the contact line runs within a contact plane that aligns with the middle of the waveguide and is parallel to the direction of propagation, both E-plane cut and H-plane cut configurations pose a significant risk of radio frequency leakage. Such a contact line usually necessitates extensive surface polishing and a high clamping force to reduce unwanted radio frequency leakage. Ultimately, waveguides cannot be affixed to other radio frequency transmission components that impose limitations on screw mounting, i.e. transmission components that do not allow for easy creation of screw holes such as transmission components made of or comprising glass panels. Consequently, interfaces in these cases may necessitate the use of other means for mounting two parts like e.g. conductive epoxies. This, however, imposes constraints on material selection due to e.g. the specific coefficient of thermal expansion properties required for compatibility or the adhesive characteristics or the electric conductivity of the material that is arranged along the contact line in the gap between the two parts facing each other. In addition, the use of conductive epoxies causes additional difficulties like e.g. the proper application of the conductive epoxy itself. Due to the conductive characteristics of such a material, any leakage of the material in the channel recess will cause interference with the electromagnetic waves that propagate along the channel recess, which affects propagation characteristics and may cause additional but unwanted leakage. Therefore, the epoxy should only be applied to the walls such that no spillover into the channel recess happens, which makes it a difficult application process for the conductive epoxy material.

[0007] Alternatively, making use of high temperature curing conductive pastes is another option for adhesively connecting two or more parts of the hollow waveguide device that have been manufactured separately, e.g. for adhesively connecting a channel body and a lid body. However, this method presents challenges as well, as the application of conductive pastes is difficult, comes with a higher cost, and demands materials with elevated temperature resistivity.

[0008] Thus, there is a need for a hollow waveguide device with low weight and small size that does not exhibit significant radio frequency leakage, but is cost-effective to manufacture.Summary of the Invention

[0009] The present disclosure relates to a hollow waveguide device as described above, characterized in that the lid body is bonded onto the channel body by means of a contact layer that is arranged between the lid body and the channel surface, that is made of a dielectric adhesive material and that completely encloses the at least one channel recess in the channel surface. Surprisingly and contrary to common knowledge of persons skilled in the art, it was demonstrated that such a contact layer made of a dielectric adhesive material that is arranged within the gap between the channel surface of the channel body and the lid body very effectively reduces unwanted radio frequency leakage through this gap, even though the dielectric adhesive material is considered to be nonconductive or isolating. Measurements performed by the applicant were able to verify that even though a dielectric adhesive material is usually considered having little or no effect on the transmission of electromagnetic waves and is thus similar to air, such a contact layer made of a suitable dielectric adhesive material significantly reduces any unwanted radio frequency leakage through a gap along the cavity that is filled by the contact layer. For most applications, the contact layer made of a dielectric adhesive material acts as if there is a full galvanic contact between the lid body and the channel body that forms an electrical conductive enclosure of the hollow waveguide in a much better way than any conventionally manufactured hollow waveguide with a conductive material or no additional material within the gap between the lid body and the channel body. Thus, the use and arrangement of a contact layer made of a dielectric adhesive material is counter-intuitive for persons skilled in the art who considers only a gap filling material with electrically conductive properties as suitable for such embodiments of hollow waveguide devices.

[0010] The bonding of the channel body with the lid body does not require the application of large forces or pressure to reduce the size of a gap between the respective surfaces of the two bodies that face each other. Thus, it is not necessary to mount the lid body onto the channel body by means of screws or any other form-fitting fastening means. By consequence, it is not necessary to arrange for screw threads and corresponding screw holes along a contact line around the channel recess within the channel body. This significantly reduces the space around the channel recess that is required for the arrangement of the screws. Furthermore, as the required forces for the bonding with a contact layer made of dielectric adhesive material are significantly less than for the mounting with screws, this results in reduced mechanical load-bearing capacity that is required for the channel body and the lid body around the channel recess. The reduced requirement of mechanical load-bearing capacity allows for a smaller minimum width of a supporting wall structure of the channel body around the channel recess that allows for further reduction of the weight and of the space requirements of the channel body and the lid body.

[0011] Also, making use of a dielectric adhesive material that affixes the lid body onto the channel surface of the channel body allows for the use of many different materials for the manufacture of the channel body and of the lid body. Thus, a lid body may be made of glass or a plastic foam material with a metallic coating that provides for the metallic walls that enclose the cavity of the hollow waveguide device. Such materials like glass or plastic foam material do not easily allow for the mounting of screws and are not suitable for conventional hollow waveguide devices with a screw connection of the two parts, i.e. of the channel body and the lid body.

[0012] For most applications and frequencies of the radio frequency electromagnetic waves for which the use of the hollow waveguide device is intended, a thickness of the contact layer perpendicular to the channel surface or the lid surface is less than 100 µm, preferably less than 50pm, more preferably less than 30 µm and most preferably less than 10 µm. Thus, the extension of a resulting gap between the lid surface and the channel surface overlapping and facing each other that is visible from the cavity inside the hollow waveguide device is small but filled by the dielectric adhesive material of the contact layer.

[0013] According to a main aspect of the invention, there is no need for using an adhesive material with high electric conductivity which usually requires the embedding of metallic particles within a matrix material with adhesive characteristics. The embedding of metallic particles usually increases the costs for suitable adhesive materials and imposes severe restrictions on compatibility and bonding characteristics of the matrix material. By making use of a dielectric adhesive material, there is a large number of different dielectric adhesive materials available at low cost that exhibit a wide range of bonding characteristics and can be used with many different surface materials of the channel body and of the lid body.

[0014] According to a favorable aspect of the invention, a minimum width of the contact layer that runs along a circumferential line around the channel recess, is larger than 25 µm in a direction parallel to the channel surface, preferably larger than 50 pm, more preferably larger than 100 µm and most preferably larger than 200 µm. A large expansion of the contact layer parallel to the channel surface provides for a substantial reduction of the radio frequency leakage as well as for a strong adhesive force and a high adhesive effect that affixes the lid body onto the channel surface of the channel body. Preferably, the dielectric adhesive material is sufficiently elastic to compensate for small surface irregularities of the channel surface and of the corresponding lid surface of the lid body to ensure a complete filling of the gap between metallic inner wall sections of the channel body and the lid body.

[0015] In yet another favorable embodiment according to the invention, the contact layer fully covers the channel surface or a lid surface of the lid body that faces the channel surface of the channel body. As the contact layer is made from a dielectric adhesive material that does not significantly affect the propagation of radio frequency electromagnetic waves, there is no need to avoid the arrangement of some parts of the contact layer inside the channel recess, i.e. within the cavity of the hollow waveguide device. A contact layer that fully covers the channel surface or the corresponding lid surface allows for a very easy preparation of such a contact layer and its application and mounting onto the channel surface or lid surface.

[0016] According to an advantageous embodiment of the invention, the contact layer is designed to form a moisture proof sealing between the channel surface and the lid body that surrounds the channel recess. Thus, there is no risk of unwanted uptake of moisture or fluids through the gap between the channel body and the lid body into the cavity of the hollow waveguide device that might interfere with the signal transmission of electromagnetic waves that propagate along the channel recess in the direction of propagation. Furthermore, the metallic inner walls that enclose the cavity of the hollow waveguide device are protected from any unwanted contact with moisture that might result in an impairment of the surface due to chemical processes or a reduction of electric conductivity of the metallic inner walls which in turn might adversely affect the signal propagation of radio frequency electromagnetic waves.

[0017] According to a favorable aspect of the invention, the contact layer of the dielectric adhesive material is made from a pre-cut film made of the dielectric adhesive material. Thus, the contact layer can be prefabricated with any shape or design of the inner and outer contour of the contact layer. For bonding the lid body onto the channel body, the prefabricated contact layer must be arranged either on the channel surface of the channel body or on the lid surface of the lid body before bringing the channel body and the lid body with the respective channel surface and lid surface facing towards each other into close contact which results in adhesive bonding of the lid surface onto the channel surface by means of the contact layer made of the dielectric adhesive material. The prefabricated contact layer can be deposited onto the channel surface or the lid surface by means of a transfer tape. Thus, it is possible to perform a fully automated prefabrication of the contact layer and subsequent deposition onto the corresponding surface of either the channel body or the lid body.

[0018] According to a further embodiment of the invention, the channel surface of the channel body is a flat surface with at least one channel recess arranged therein, and that the lid body comprises a lid surface that is a flat surface that faces the channel surface of the channel body. Flat surfaces are easily manufactured and allow for an easy and cost-effective arrangement of the contact layer in between the two flat surfaces of the channel body and of the lid body. If required, polishing or any other treatment of the channel surface and of the lid surface can be easily performed if both surfaces are flat surfaces.

[0019] It is considered another very advantageous aspect of the invention that the channel body does not have to be designed in such a way that large screwing forces can be absorbed and dissipated. In addition, there is no need for openings or boreholes within the lid body that are required for the mounting of screws or similar mounting devices.

[0020] According to a very favorable embodiment of the invention, the lid body can be formed by a printed circuit board comprising a substrate layer made of a dielectric material and with an electrically conductive coating that covers at least a part of the substrate layer. Such a manufacture of a hollow wave guide that is arranged at the surface of a printed circuit board is very easy, as it is only required to bond the channel body onto the coated surface of the printed circuit board. The contact layer that is required for bonding the channel body onto the printed circuit board can be previously mounted onto the coated surface of the printed circuit board or onto the channel surface of the channel body. Afterwards, it is only required to bring the channel body in contact with the printed circuit board and to apply a contact pressure that will be sufficient for a reliable and permanent fastening of the channel body with the printed circuit board. As no screws or similar mounting devices are required for mounting the channel body onto the printed circuit board, there is no need for openings or boreholes within the printed circuit board. In addition, the mechanical stress applied to the printed circuit board during fastening of the channel body onto the printed circuit board will be very small and reduces the risk of unwanted damage to the printed circuit board or to any electronic components that have been mounted onto the printed circuit board before.

[0021] The hollow waveguide device as described above is considered to be particularly advantageous for mounting the channel body onto substrate layers that do not allow for openings or boreholes that are subsequently introduced into the substrate layer like e.g. substrate layers made of glass or a ceramic material, whereby the lid body is formed by a part of such a substrate layer that only requires a previously applied coating of an electrically conductive material like e.g. metal.Brief description of the drawings

[0022] The present invention will be more fully understood, and further features will become apparent, when reference is made to the following detailed description and the accompanying drawings. The drawings are merely representative and are not intended to limit the scope of the claims. In fact, those of ordinary skill in the art may appreciate upon reading the following specification and viewing the present drawings that various modifications and variations can be made thereto without deviating from the innovative concepts of the invention. Like parts depicted in the drawings are referred to by the same reference numerals. Fig. 1 illustrates a perspective view of a hollow waveguide device, Fig. 2 illustrates a sectional view of the hollow waveguide device of Fig. 1 along a sectional plane II-II in Fig. 1, Figs. 3 to 5 illustrate several steps of a method for manufacture of yet another embodiment of a hollow waveguide device. Figs. 6 and 7 illustrate a perspective view of yet another embodiment of a hollow waveguide device in an expanded view and as fully mounted device, Fig. 8 illustrates a sectional view of the hollow waveguide device of Figs. 6 and 7 along a sectional plane VIII-VIII in Fig. 7, Fig. 9 illustrates a perspective view of yet another embodiment of a hollow waveguide device, and Fig. 10 illustrates a sectional view of the hollow waveguide device of Fig. 9 along a sectional plane X-X in Fig. 9.

[0023] Figs. 1 and 2 illustrate a hollow waveguide device 1 with a channel body 2 and a lid body 3 that is bonded onto the channel body 2. The lid body 3 comprises a first opening 4 and a second opening 5 that are at a distance towards each other and allow for the insertion and extraction of electromagnetic waves into and out of a cavity 6 that is formed within the hollow waveguide device 1. The hollow waveguide device 1 has a cuboid, elongated shape with a large extension along a direction of propagation 7 of the electromagnetic waves within the cavity 6. The first and second opening 4, 5 within the lid body 3 have a large distance along the direction of propagation 7. A largest diameter of a cross-sectional surface of the cavity 6 perpendicular to the direction of propagation 7 as shown in Fig. 2 is much less than the extension of the hollow waveguide device 1 in the direction of propagation 7.

[0024] The channel body 2 and the lid body 3 are made of a metallic material with electric conductivity properties that allow for a low-loss transmission of radio frequency electromagnetic waves along the cavity 6 within the hollow waveguide device 1. The channel body 2 comprises a channel recess 8 that is enclosed by a bottom wall and side walls. The channel recess 8 is designed as a recess within a channel surface 9 and that faces the lid body 3. Correspondingly, a lid surface 10 of the lid body 3 faces the channel body 2.

[0025] The lid body 3 is bonded to the channel body 2 with a contact layer 11 made of a dielectric adhesive material. The contact layer 11 covers the overlapping regions of the channel surface 9 of the channel body 2 and the lid surface 10 of the lid body 3 and fills a gap 12 between the channel surface 9 of the channel body 2 and the lid surface 10 of the lid body 3 that runs along a circumferential line around the channel recess 8. Even though this contact layer 11 is made of a dielectric material with an electric conductivity that is less than 1 S / m and preferably less than 10 -3< S / m, which is considered as being transparent for radio frequency electromagnetic waves, the contact layer 11 significantly reduces any unwanted leakage of radio frequency electromagnetic waves through the gap 12.

[0026] As there is no need for the arrangement of a number of screws along a circumferential line around the channel recess 8, the channel surface 9 has a very small footprint and the walls enclosing the cavity 6 have a small thickness. Thus, the hollow waveguide device 1 is less bulky and considerably lighter than conventional hollow waveguide devices with a lid body that is screwed onto the channel body.

[0027] Figs. 3 to 5 schematically illustrate a method for manufacturing a hollow waveguide device 1 as shown in Figs. 1 and 2. The method comprises a body manufacturing step as illustrated in Fig. 3. The body manufacturing step includes the manufacture of the channel body 2 with at least one channel recess 8 and the lid body 3.

[0028] The method also comprises a mounting step including arranging the contact layer 11 between the lid surface 10 and the channel surface 9, whereby the contact layer 11 is made of a dielectric adhesive material with a thickness of less than 100 µm and completely encloses the at least one channel recess 8 in the channel surface 9. The contact layer 11 is prefabricated by cutting the shape of the contact layer 11 from a film of the dielectric adhesive material. The prefabricated contact layer 11 is shown in Fig. 4.

[0029] The mounting step further includes bonding the lid surface 10 of the lid body 3 to the channel surface 9 of the channel body 2 with the contact layer 11 in between the lid surface 10 and the channel surface 9. Due to the adhesive properties of the contact layer 11, the lid body 3 is affixed onto the channel body 2 and securely fixed in this position, thus forming the hollow waveguide device 1 with the cavity 6 inside. As illustrated in Fig. 5, the gap 12 between the lid body 3 and the channel body 2 that runs along a circumferential line on the channel surface 9 around the channel recess 8 is filled by the dielectric adhesive material of the contact layer 11 and significantly reduces any unwanted leakage of radio frequency electromagnetic waves that propagate through the cavity 6 along the direction of propagation 7.

[0030] By way of example, Figs. 6 to 8 schematically illustrate another embodiment of a hollow waveguide device. The channel body 2 has a cuboid, elongated shape similar to the channel body as shown in Figs. 1 to 5, with a large extension along the direction of propagation 7 of the electromagnetic waves within the cavity 6. However, the first opening 4 and the second opening 5 are arranged in the opposite end faces of the channel body 2 and not within the lid body 3.

[0031] Thus, the lid body 3 is formed by an even substrate layer made from a suitable material, whereby the lid body 3 does not comprise any openings or boreholes. The dimensions of the lid body 3, i.e. of the lid surface 10 matching the dimensions of the channel body 2 and in particular of the channel surface 9.

[0032] Similarly, the contact layer 11 is formed by a film made of an adhesive material or coated with an adhesive material. The dimensions of the contact layer 11 match the dimensions of the lid surface 10 and of the corresponding channel surface 9. There is no need for a cut-out within the contact layer 11 that requires prefabrication of the contact layer 11 and precise alignment of the contact layer 11 with the corresponding lid surface 10 and channel surface 9 that are facing each other. As the contact layer 11 is made from a dielectric material, the propagation of radio frequency electromagnetic waves within the cavity 6 of the hollow waveguide device 1 is not affected or impaired by the part of the contact layer 11 that is arranged at the lid surface 10 and not covered by the channel surface 9, but inside of the cavity 6 that is enclosed by electrically conductive surfaces of the hollow waveguide device 1.

[0033] Another embodiment of the hollow waveguide device 1 is schematically illustrated in a perspective view of Fig. 9 and in a sectional view of Fig.. The lid body 3 is formed by a printed circuit board 13 with a substrate layer 14 made of a dielectric material like plastics or glass, and with an electrically conductive coating 15 made of a e.g. a metallic material. The surface area 16 of the coating 15 is larger than the surface area of the channel surface 9. The channel body 2 is mounted on top of the coating 15 with the channel surface 9 facing the printed circuit board 13. In order to fasten the channel body 2 to the printed circuit board 13, the contact layer 11 made of the dielectric adhesive material is arranged in between the channel surface 9 of the channel body 2 and the coating 15 of the substrate layer 14 of the printed circuit board 13. The surface area of the contact layer 11 is larger than the surface area of the channel surface 9 and does not comprise any openings or cut-outs that overlap or match the channel recess 8. The contact layer 11 can be attached to either the coating 15 or the channel surface 9 before the channel body 2 is mounted onto the printed circuit board 13. The contact layer 11 can be applied to the respective surface as a film made of the dielectric adhesive material, or as an curable coating that is added on top of the coating 15 and made of an initially viscous and subsequently hardening material. The printed circuit board 13 may comprise additional electronic components like e.g. additional conductor tracks 16 or capacitors 17 etc.

Claims

1. Hollow waveguide device (1) for radio frequency electromagnetic waves with a cavity (6) that extends in one direction of propagation (7) of the electromagnetic waves, whereby a largest diameter of a cross-sectional surface of the cavity (6) perpendicular to the direction of propagation (7) is less than the extension in the direction of propagation (7), whereby the cavity (6) is enclosed by metallic inner walls of the hollow waveguide device (1), whereby the hollow waveguide device (1) comprises a channel body (2) with at least one channel recess (8) that extends in the direction of propagation (7) and that is accessible from a channel surface (9) of the channel body (2), and that further comprises a lid body (3) that is mounted onto the channel surface (9) of the channel body (2) and that covers the at least one channel recess (8) to form the electromagnetic wave conducting cavity (6) of the hollow waveguide (1), characterized in that the lid body (3) is bonded onto the channel body (2) by means of a contact layer (11) that is arranged between the lid body (3) and the channel surface (9) of the channel body (2), that is made of a dielectric adhesive material and that completely encloses the at least one channel recess (8) in the channel surface (9) .

2. Hollow waveguide device (1) according to claim 1, characterized in that along a circumferential line around the channel recess (8), a minimum width of the contact layer (11) in a direction parallel to the channel surface (9) is larger than 25 µm, preferably larger than 50 pm, more preferably larger than 100 µm and most preferably larger than 200 µm.

3. Hollow waveguide device (1) according to claim 1 or claim 2, characterized in that along a circumferential line around the channel recess (8), a minimum thickness of the contact layer (11) in a direction perpendicular to the channel surface (9) is less than 100 µm, preferably less than 50 pm, more preferably larger than 30 µm and most preferably less than 10 µm.

4. Hollow waveguide device (1) according to any of the preceding claims, characterized in that the contact layer (11) fully covers the channel surface (9) or a lid surface (10) of the lid body (3) that faces the channel surface (9) of the channel body (2).

5. Hollow waveguide device (1) according to any of the preceding claims, characterized in that the contact layer (11) is designed to form a moisture proof sealing between the channel surface (9) and the lid body (3) that surrounds the channel recess (8).

6. Hollow waveguide device (1) according to any of the preceding claims, characterized in that the contact layer (11) of the dielectric adhesive material is made from a pre-cut film made of the dielectric adhesive material.

7. Hollow waveguide device (1) according to claim 6, characterized in that the contact layer (11) of the dielectric adhesive material is prefabricated with a cut-out within the pre-cut film.

8. Hollow waveguide device (1) according to any of the preceding claims, characterized in that the channel surface (8) of the channel body (2) is a flat surface with at least one channel recess (8) arranged therein, and that the lid body (3) comprises a lid surface (10) that is a flat surface that faces the channel surface (9) of the channel body (2).

9. Hollow waveguide device (1) according to claim 8, characterized in that the lid body (3) is formed by a printed circuit board (13) comprising a substrate layer (14) made of a dielectric material and with an electrically conductive coating (15) that covers at least a part of the substrate layer (14).

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