Patent Publication Number: US-9893399-B2

Title: Waveguide filter

Description:
This application is a continuation of International Application No. PCT/CN2013/074208, filed on Apr. 15, 2013, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the field of wireless communications technologies, and in particular, to a waveguide filter. 
     BACKGROUND 
     A waveguide is an apparatus for transmitting an electromagnetic wave in radio fields such as radio communication, radars, and navigation, and is a basic circuit unit in a circuit system. Generally, a circuit system has multiple waveguides, and therefore, adaptation is required between a waveguide and another waveguide or between a waveguide and another sub-circuit. However, if a filter with a frequency-selecting function, that is, a waveguide filter, is formed in an adaptation process, a quantity of filters in the circuit system may be reduced to some extent. 
     A waveguide filter commonly used in a microwave and millimeter wave circuit may be filter based on a metal waveguide and a filter based on a planar circuit such as a microstrip line and a coplanar line. The filter based on a metal waveguide generally has advantages such as a high Q value (quality factor), a low loss, and desirable selectivity. The filter based on planar circuit technologies such as a microstrip line and a coplanar line has a feature of easy integration into an active circuit. A filter based on a substrate integrated waveguide has such advantages of a planar circuit as being easily integrated and conveniently manufactured, and also has excellent performance similar to that of a metal waveguide filter. 
     However, the foregoing waveguides that form a filter are generally disposed at a same layer of circuit. When the waveguides are applied to multiple layers of circuits, an extra transition structure needs to be added to implement inter-layer adaptation, which imperceptibly increases complexity of a circuit structure and a circuit loss. 
     SUMMARY 
     An embodiment of the present invention provides a waveguide filter, so as to resolve a problem of a complex circuit structure and a high circuit loss that are caused when a waveguide filter is applied at different layers of circuits. 
     To achieve the foregoing objectives, the following technical solutions are used in the embodiment of the present invention uses. 
     A first aspect of the present invention provides a waveguide filter, where the waveguide filter includes a first waveguide at an upper layer and a second waveguide at a lower layer, the first waveguide and the second waveguide are isolated from each other by a metal isolation layer, the first waveguide forms a first resonant cavity, the second waveguide forms a second resonant cavity, the first resonant cavity and the second resonant cavity overlap each other, and a coupling slot is disposed at the metal isolation layer in an overlapping area. 
     In a first possible implementation manner, the first waveguide includes a dielectric substrate, an upper surface of the dielectric substrate is covered by a first metal layer, a lower surface of the dielectric substrate is covered by a second metal layer, multiple metalized via holes that run through the first metal layer, the dielectric substrate, and the second metal layer are disposed in the dielectric substrate, and the dielectric substrate, the multiple metalized via holes, the first metal layer, and the second metal layer form the first resonant cavity; the second waveguide is a metal waveguide with a pierced upper part, and the second metal layer and a cavity inside the second waveguide form the second resonant cavity; and the metal isolation layer is the second metal layer. 
     In a second possible implementation manner, the first waveguide includes a first dielectric substrate, an upper surface of the first dielectric substrate is covered by a first metal layer, a lower surface of the first dielectric substrate is covered by a second metal layer, multiple first metalized via holes that run through the first metal layer, the first dielectric substrate, and the second metal layer are disposed in the first dielectric substrate, and the first dielectric substrate, the multiple first metalized via holes, the first metal layer, and the second metal layer form the first resonant cavity; the second waveguide includes a second dielectric substrate, an upper surface of the second dielectric substrate is covered by a third metal layer, a lower surface of the second dielectric substrate is covered by a fourth metal layer, multiple second metalized via holes that run through the third metal layer, the second dielectric substrate, and the fourth metal layer are disposed in the second dielectric substrate, and the second dielectric substrate, the multiple second metalized via holes, the third metal layer, and the fourth metal layer form the second resonant cavity; and the metal isolation layer is the second metal layer and the third metal layer. 
     In a third possible implementation manner, the first waveguide is a hollow metal waveguide, and a cavity inside the first waveguide forms the first resonant cavity; the second waveguide is a metal waveguide with a pierced upper part, and a metal layer on a lower surface of the first waveguide and a cavity inside the second waveguide form the second resonant cavity; and the metal isolation layer is the metal layer on the lower surface of the first waveguide. 
     With reference to the first aspect, the first possible implementation manner of the first aspect, the second possible implementation manner of the first aspect, or the third possible implementation manner of the first aspect, in a fourth possible implementation manner, both the first resonant cavity and the second resonant cavity are circular. 
     With reference to the fourth possible implementation manner of the first aspect, in a fifth possible implementation manner, the coupling slot is located at a central position of the overlapping area, and an extension direction of the coupling slot is perpendicular to a line connecting a circle center of the first resonant cavity and a circle center of the second resonant cavity. 
     With reference to the first aspect, the first possible implementation manner of the first aspect, the second possible implementation manner of the first aspect, the third possible implementation manner of the first aspect, the fourth possible implementation manner of the first aspect, or the fifth possible implementation manner of the first aspect, in a sixth possible implementation manner, the first waveguide further includes a first feeding part and a first feeding window that are interconnected, the first feeding window is located on a side wall of the first resonant cavity, the first feeding part is a waveguide section of the first waveguide, and the first feeding part is connected to the first resonant cavity by the first feeding window; and the second waveguide further includes a second feeding part and a second feeding window that are interconnected, the second feeding window is located on a side wall of the second resonant cavity, the second feeding part is a waveguide section of the second waveguide, and the second feeding part is connected to the second resonant cavity by the second feeding window. 
     With reference to the sixth possible implementation manner of the first aspect, in a seventh possible implementation manner, the first feeding window is parallel to the second feeding window, and an included angle between the line connecting of the circle center of the first resonant cavity and the circle center of the second resonant cavity and a direction perpendicular to the first feeding window is α, where 90°≧α≧45°. 
     With reference to the seventh possible implementation manner of the first aspect, in an eighth possible implementation manner, a width of the first feeding part and a width of the second feeding part is greater than a width corresponding to a cut-off frequency. 
     According to the waveguide filter provided by the embodiment of the present invention, a first waveguide and a second waveguide are isolated from each other by a metal isolation layer, the first waveguide forms a first resonant cavity, the second waveguide forms a second resonant cavity, the first resonant cavity and the second resonant cavity overlap each other, and a coupling slot is disposed at the metal isolation layer in an overlapping area, so that the first resonant cavity and the second resonant cavity that are disposed one above the other are coupled and connected by the coupling slot disposed in the overlapping area, adaptation between the first waveguide and the second waveguide is also implemented by using the coupling slot, and the waveguide filter is formed, where no other transition structures are added in an adaptation process, a circuit structure is relatively simple, and a circuit loss is low. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the technical solutions in the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings required for describing the embodiments or the prior art. Apparently, the accompanying drawings in the following description show merely some embodiments of the present invention, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG. 1  is a schematic structural diagram of a waveguide filter according to an embodiment of the present invention; 
         FIG. 2  is a schematic structural diagram of a first waveguide shown in  FIG. 1 ; 
         FIG. 3  is a schematic structural diagram of a second waveguide shown in  FIG. 1 ; 
         FIG. 4  is another schematic structural diagram of a waveguide filter according to an embodiment of the present invention; and 
         FIG. 5  is a top view of the waveguide filter shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The following clearly describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are merely some but not all of the embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. 
     As shown in  FIG. 1  and  FIG. 4 , an embodiment of the present invention provides a waveguide filter, where the waveguide filter includes a first waveguide  1  at an upper layer and a second waveguide  2  at a lower layer, the first waveguide  1  and the second waveguide  2  are isolated from each other by a metal isolation layer  111 , the first waveguide  1  forms a first resonant cavity  11 , and the second waveguide  2  forms a second resonant cavity  21 , the first resonant cavity  11  and the second resonant cavity  21  overlap each other, and a coupling slot  3  is disposed at the metal isolation layer  111  in an overlapping area M. 
     According to the waveguide filter provided by the embodiment of the present invention, a first waveguide  1  and a second waveguide  2  are isolated from each other by a metal isolation layer  111 , the first waveguide  1  forms a first resonant cavity  11 , the second waveguide  2  forms a second resonant cavity  21 , the first resonant cavity  11  and the second resonant cavity  21  overlap each other, and a coupling slot  3  is disposed at the metal isolation layer  111  in an overlapping area M, so that the first resonant cavity  11  and the second resonant cavity  21  that are disposed one above the other are coupled and connected by the coupling slot  3  disposed in the overlapping area, and adaptation between the first waveguide  1  and the second waveguide  2  is also implemented by using the coupling slot  3 , where no other transition structures are added in an adaptation process, a circuit structure is relatively simple, and a circuit loss is low. 
     It can be understood that in the foregoing embodiment, it may also be that the first waveguide is at the lower layer, the second waveguide is at the upper layer, and the first waveguide and the second waveguide may be mechanically fastened in a manner such as by using a bolt or a conductive adhesive. 
     In addition, it should be noted for the foregoing embodiment that a positional relationship between the first resonant cavity and the second resonant cavity determines a form of the overlapping area, and the first resonant cavity and the second resonant cavity have the following positional relationships. 
     A: Overlapping completely, that is, the first resonant cavity and the second resonant cavity are completely the same in size and shape, and completely overlap when seen from above, and in this case, an overlapping area is an area covered by the first resonant cavity or the second resonant cavity, which is generally applicable to a case that the first waveguide and the second waveguide are waveguides of a same type. 
     B: Intersecting each other, that is, as shown in  FIG. 1 , the first resonant cavity  11  and the second resonant cavity  21  intersect and overlap, and an overlapping area is an area M that is covered by both the first resonant cavity  11  and the second resonant cavity  21 , which is applicable to a case that the first waveguide and the second waveguide are waveguides of a same type or waveguides of different types. 
     Specifically, shapes, sizes, and the positional relationship of the first resonant cavity and the second resonant cavity need to be determined by using a simulation result obtained by simulation software, where conditions on which simulation depends include a working mode of the filter (for example, a dominant mode or a dual mode), a frequency range of an electromagnetic wave that is allowed to pass, and a coupling coefficient of the first resonant cavity and the second resonant cavity. 
     Preferably, both the first resonant cavity and the second resonant cavity are circular. In this way, the filter can work in a TM110 mode (TM110 is one of resonant modes of a resonant cavity, and for a circular waveguide resonant cavity, represents a distribution of an electromagnetic field at a higher order mode). 
     Preferably, as shown in  FIG. 5 , the coupling slot  3  is disposed at a central position of the overlapping area, and an extension direction of the coupling slot  3  is perpendicular to a line connecting a circle center O 1  of the first resonant cavity  11  and a circle center O 2  of the second resonant cavity  21 . A reason is that getting closer to the central position of the overlapping area indicates a larger coupling coefficient of the filter and more energy coupling between the resonant cavities of the filter. In actual design, a size and a position of the coupling slot need to be optimized by using simulation software, so as to achieve a theoretically satisfying coupling coefficient. Similarly, that the extension direction of the coupling slot  3  is perpendicular to the line connecting the circle center O 1  of the first resonant cavity  11  and the circle center O 2  of the second resonant cavity  21  is more conducive to energy coupling and transmission between two waveguides and determining of the coupling coefficient. 
     As shown in  FIG. 1  to  FIG. 5 , the first waveguide  1  further includes a first feeding part  12  and a first feeding window  13  that are interconnected, the first feeding window  13  is on a side wall of the first resonant cavity  11 , the first feeding part  12  is a first waveguide section of the first waveguide  1 , and the first feeding part  12  is connected to the first resonant cavity  11  by the first feeding window  13 ; and the second waveguide  2  further includes a second feeding part  22  and a second feeding window  23  that are interconnected, the second feeding window  23  is disposed on a side wall of the second resonant cavity  21 , the second feeding part  22  is a second waveguide section disposed on the second waveguide  2 , and the second feeding part  22  is connected to the second resonant cavity  21  by the second feeding window  23 . In this way, feeding the filter may be performed at the first feeding part or the second feeding part. When the feeding is performed at the first feeding part, an electromagnetic wave passes through the first feeding window, the first resonant cavity, the second resonant cavity, and finally the second feeding window, and is output from the second feeding part. When the feeding is performed at the second feeding part, an electromagnetic wave passes through the second feeding window, the second resonant cavity, the first resonant cavity, and finally the first feeding window, and is output from the first feeding part. Certainly, the present invention is not limited to this. Alternatively, the first feeding window may be disposed on an upper surface of the first resonant cavity, and the second feeding window may be disposed on a lower surface of the second resonant cavity, so that feeding may be performed on an upper part or a bottom part of the filter. 
     A width of the first feeding part and a width of the second feeding part that are in the foregoing embodiment are preferably greater than a width corresponding to a cut-off frequency, so as to ensure purity of a filtered wave. 
     Preferably, the first feeding window is parallel to the second feeding window, and an included angle between the line connecting the circle center of the first resonant cavity and the circle center of the second resonant cavity and a direction perpendicular to the first feeding window is α, where 90°≧α≧45°. This is conducive to excitation of the dual mode, so that the filter works in the dual mode. When the first resonant cavity and the second resonant cavity are in the relationship of overlapping completely, the circle center O 1  coincides with the circle center O 2 , and in this case, a positional relationship between the first feeding window and the second feeding window needs to be correspondingly adjusted to excite the dual mode. 
     In addition, a filter based on a metal waveguide and a filter based on a substrate integrated waveguide generally have advantages such as a high Q value (Quality factor, quality factor), a low loss, and desirable selectivity. Further, the filter based on a substrate integrated waveguide further has such advantages of a planar circuit as being easily integrated and conveniently manufactured, resulting in great suitability for design and mass production of microwave and millimeter wave integrated circuits. Therefore, the first waveguide in the foregoing embodiment may be a substrate integrated waveguide or a metal waveguide, and the second waveguide may also be a substrate integrated waveguide or a metal waveguide. Specific combination and adaptation forms are as follows. 
     1. When the first waveguide is a substrate integrated waveguide, and the second waveguide is a metal waveguide, the first waveguide and the second waveguide form, after adaptation, a waveguide filter shown in  FIG. 1 . 
     In this case, the first waveguide is preferably a substrate integrated waveguide shown in  FIG. 2 , and includes a dielectric substrate  10 , a first metal layer  10   a  covering an upper surface of the dielectric substrate  10 , and a second metal layer  10   b  covering a lower surface of the dielectric substrate  10 , where multiple metalized via holes  10   c  that run through the first metal layer  10   a , the dielectric substrate  10 , and the second metal layer  10   b  are disposed in the dielectric substrate  10 , and the dielectric substrate  10 , the metalized via holes  10   c , the first metal layer  10   a , and the second metal layer  10   b  form the first resonant cavity  11 . The second waveguide is preferably a metal waveguide, with a pierced upper part, shown in  FIG. 3 , and the second metal layer  10   b  and a cavity inside the second waveguide form the second resonant cavity  21 . The metalized via holes  10   c  may be manufactured by using a common printed circuit board (PCB) technology. 
     In this embodiment, a specific adaptation method for adaptation between the first waveguide and the second waveguide may be: firstly, removing a metal layer on an upper surface of a hollow metal waveguide (or directly machining a metal waveguide of a structure with a pierced upper part, as shown in  FIG. 3 ), and disposing the coupling slot  3  at a corresponding position at the second metal layer  10   b  on a lower surface of the substrate integrated waveguide (the coupling slot may be manufactured by using the common printed circuit board technology); secondly, superposing the substrate integrated waveguide on the metal waveguide, and making the substrate integrated waveguide and the metal waveguide fit closely; and finally, mechanically fastening the first waveguide and the second waveguide in a manner such as by using a bolt or a conductive adhesive. 
     A result of combination is that the substrate integrated waveguide at an upper layer and the metal waveguide at a lower layer are isolated from each other by the second metal layer  10   b , that is, a metal isolation layer, and the first resonant cavity and the second resonant cavity are coupled and connected by the coupling slot. In this way, adaptation between the substrate integrated waveguide and the metal waveguide is implemented by using the coupling slot, so as to form the waveguide filter shown in  FIG. 1 , and adaptation between waveguides of different types is implemented, where an adaptation structure is simple. 
     2. When both the first waveguide and the second waveguide are substrate integrated waveguides, the first waveguide and the second waveguide form, after adaptation, a waveguide filter shown in  FIG. 4 . 
     In this case, the first waveguide  1  includes a first dielectric substrate  10 , an upper surface of the first dielectric substrate  10  is covered by a first metal layer  101 , a lower surface of the first dielectric substrate  10  is covered by a second metal layer  102 , multiple first metalized via holes  103  that run through the first metal layer  101 , the first dielectric substrate  10 , and the second metal layer  102  are disposed in the first dielectric substrate  10 , and the first dielectric substrate  10 , the multiple first metalized via holes  103 , the first metal layer  101 , and the second metal layer  102  form the first resonant cavity  11 . 
     The second waveguide  2  includes a second dielectric substrate  20 , an upper surface of the second dielectric substrate  20  is covered by a third metal layer  201 , a lower surface of the second dielectric substrate  20  is covered by a fourth metal layer  202 , multiple second metalized via holes  203  that run through the third metal layer  201 , the second dielectric substrate  20 , and the fourth metal layer  202  are disposed in the second dielectric substrate  20 , and the second dielectric substrate  20 , the multiple second metalized via holes  203 , the third metal layer  201 , and the fourth metal  202  layer form the second resonant cavity  21 . 
     In this way, the metal isolation layer is the second metal layer  102  and the third metal layer  201 . 
     A specific adaptation method of the first waveguide and the second waveguide is: firstly, disposing the coupling slot  3  at a corresponding position that is at the second metal layer  102  on a lower surface of the first waveguide  1  and at the third metal layer  201  on an upper surface of the second waveguide  2 , where the coupling slot runs through the second metal layer  102  and the third metal layer  201 ; secondly, stacking the two substrate integrated waveguides together, and making the two substrate integrated waveguides fit closely; and finally, mechanically fastening the two substrate integrated waveguides in a manner such as by using a bolt or a conductive adhesive. 
     A result of combination is that the first waveguide and the second waveguide are isolated from each other by the second metal layer on the lower surface of the first waveguide and the third metal layer on the upper surface of the second waveguide, and the first resonant cavity and a second resonant cavity are coupled and connected by the coupling slot. In this way, adaptation between the first waveguide and the second waveguide is implemented by using the coupling slot, so as to form the waveguide filter shown in  FIG. 4 , and adaptation between waveguides of a same type is implemented, where an adaptation structure is simple. 
     3. An adaptation structure in a case in which both the first waveguide and the second waveguide are metal waveguides. 
     In this case, the first waveguide is a hollow metal waveguide, and a cavity inside the first waveguide forms the first resonant cavity; the second waveguide is a metal waveguide with a pierced upper part, and a metal layer on a lower surface of the first waveguide and a cavity inside the second waveguide form the second resonant cavity; and the metal isolation layer is the metal layer on the lower surface of the first waveguide. 
     A specific adaptation method of the first waveguide and the second waveguide is: firstly, removing a metal layer on an upper surface of the hollow metal waveguide (or directly machining, during manufacturing, a metal waveguide of a structure with a pierced upper part) to obtain the second waveguide; and disposing a coupling slot at a corresponding position at the metal layer on the lower surface of the first waveguide (that is, the hollow metal waveguide); secondly, stacking the two metal waveguides together, and making the two metal waveguides fit closely; and finally, mechanically fastening the two metal waveguides in a manner such as by using a bolt or a conductive adhesive. The first resonant cavity and the second resonant cavity are isolated from each other by one metal layer, and are coupled and connected by the coupling slot disposed at the metal layer. In this way, adaptation between the first waveguide and the second waveguide is implemented by using the coupling slot, so as to form the waveguide filter, and adaptation between waveguides of a same type is implemented, where an adaptation structure is simple. 
     4. An adaptation structure in a case in which the first waveguide is a metal waveguide, and the second waveguide is a substrate integrated waveguide. The adaptation structure is similar to the adaptation structure in which the first waveguide is a substrate integrated waveguide and the second waveguide is a metal waveguide, and a difference lies in that a first resonant cavity is a metal waveguide with a pierced lower part. 
     The foregoing descriptions are merely specific embodiments of the present invention, but are not intended to limit the protection scope of the present invention. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in the present invention shall fall within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.