Patent Publication Number: US-10333189-B2

Title: Tunable filter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2014/094235, filed on Dec. 18, 2014, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the field of filter technologies, and in particular, to a tunable filter. 
     BACKGROUND 
     As wireless communication develops, a requirement for a microwave filter increases. To meet different application environments, different filter structures appear. A tunable cavity filter is widely applied to a communications system due to its features such as a low passband insertion loss, high stopband inhibition, tuning convenience, and a relative high power processing capacity. 
     For an E-plane filter, by means of precision control over a diaphragm, a frequency adjustment screw and a coupling adjustment screw may be cancelled, and commissioning of the filter is not required, which helps implement a tunable structure of a high-frequency microwave filter. A structure of an E-plane filter in the prior art is: a metal plate and a dielectric slice are disposed inside a rectangular waveguide tube, and a motor is used to drive the dielectric slice to move, to change a relative position relationship between the dielectric slice and the metal plate, so as to adjust a frequency of the filter. However, the dielectric slice in the structure of this type of E-plane filter is in an integral sheet-like structure, the dielectric slice stretches across a resonant cavity inside the rectangular waveguide tube of the filter, and the dielectric slice has a very low requirement for a dielectric constant. Such a dielectric slice has a very small thickness, is hard in manufacturing, and is poor in process reliability. In addition, because the dielectric slice has relatively weak hardness, a shock resistance capability is poor when the dielectric slice is assembled in the E-plane filter. Because a shock of the E-plane filter easily causes a position change of the dielectric slice, performance of the E-plane filter is affected. As a result, a frequency and performance of the E-plane filter are unstable. 
     SUMMARY 
     An objective of an embodiment of the present invention is to provide an E-plane tunable filter having good process reliability, and a frequency and performance of the E-plane tunable filter have good stability. 
     The embodiment of the present invention provides a tunable filter, including a first waveguide body, a second waveguide body, a metal plate, a tuning piece, and a driving piece, where a first cavity is disposed in the first waveguide body, a second cavity is disposed in the second waveguide body, the first waveguide body is in butt joint with the second waveguide body, an input end and an output end are formed on both ends of a juncture of the first waveguide body and the second waveguide body, and an electromagnetic wave in the tunable filter is propagated from the input end to the output end; the metal plate is sandwiched between the first waveguide body and the second waveguide body, multiple windows are disposed on the metal plate, the multiple windows are distributed along a propagation direction of the electromagnetic wave of the tunable filter, and the first cavity and the second cavity are in communication and are symmetrically distributed on both sides of the metal plate; the tuning piece includes a dielectric pull-rod and multiple metal sheets connected to the dielectric pull-rod, the dielectric pull-rod traverses the first waveguide body, the dielectric pull-rod protrudes out of the first waveguide body and is connected to the driving piece, the multiple metal sheets are disposed inside the first cavity, and the multiple metal sheets and the multiple windows are distributed in a same manner and are disposed in a one-to-one correspondence, to form a resonant cavity; and the driving piece drives the tuning piece to move relative to the metal plate, to change a size of the resonant cavity, so as to adjust a frequency of the tunable filter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To describe the technical solutions in the embodiments of the present invention more clearly, the following briefly describes the accompanying drawings required for describing the embodiments. 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 three-dimensional schematic diagram of a tunable filter according to an implementation manner of the present invention; 
         FIG. 2  is a three-dimensional exploded schematic diagram of a tunable filter from a first direction according to an implementation manner of the present invention; 
         FIG. 3  is a three-dimensional exploded schematic diagram of a tunable filter from a second direction according to an implementation manner of the present invention; and 
         FIG. 4  is a partial schematic diagram of a structure in which a tuning piece and a driving piece of a tunable filter are used together according to an implementation manner of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following clearly describes the technical solutions in the implementation manners of the present invention with reference to the accompanying drawings in the implementation manners of the present invention. 
     The present invention relates to a tunable filter. In an implementation manner, the tunable filter provided in the present invention is a tunable band-pass filter. Further, the tunable filter provided in the present invention is a cuboid-shaped waveguide filter. 
     For a detailed structure of the tunable filter in the present invention, refer to  FIG. 1 ,  FIG. 2 , and  FIG. 3 . The tunable filter includes a first waveguide body  10 , a second waveguide body  20 , a metal plate  30 , a tuning piece  40 , and a driving piece  50 . 
     A first cavity  11  is disposed in the first waveguide body  10 . Specifically, in this implementation manner, the first waveguide body  10  is in a cuboid shape. In another implementation manner, a shape of the first waveguide body  10  is not limited to the cuboid shape, and may be a cylinder or another shape. The first waveguide body  10  includes a first butt-joint face  13  and a first interface face  15  that extend along a length direction of the first waveguide body  10 , and the first butt-joint face  13  and the first interface face  15  are disposed to be adjacent and are perpendicular to each other. The first cavity  11  extends along the length direction of the first waveguide body  10 , and the length direction of the first waveguide body  10  is a propagation direction of an electromagnetic wave of the tunable filter in the present invention. The first cavity  11  extends inwards the first waveguide body  10  from the first butt-joint face  13 , and both ends of the first cavity  11  separately lead to the first interface face  15 . That is, a notch  152  is disposed at each of both ends of the first interface face  15 , and the two notches  152  are configured to enable an exterior of the first waveguide body  10  to communicate with the first cavity  11 . Projection of the first cavity  11  on the first interface face  15  is a rectangle, but is not limited to a rectangle, and may also be a trapezoid or another shape. In another implementation manner of the present invention, the first waveguide body  10  is in a cylinder shape, the first cavity  11  extends along an axial direction of the first waveguide body  10 , and the length direction of the first waveguide body  10  is a propagation direction of an electromagnetic wave of the tunable filter in the present invention. 
     The first waveguide body  10  further includes a first end face  17  perpendicularly connected between the first butt-joint face  13  and the first interface face  15 . A first positioning hole  16  and a second positioning hole  18  are further disposed on the first waveguide body  10 , where the first positioning hole  16  is communicated between the first end face  17  and the first cavity  11 , and the second positioning hole  18  is opposite to the first positioning hole  16  and is located on a side of the first cavity  11  that is away from the first positioning hole  16 . The second positioning hole  18  may be a blind hole or a through hole. 
     A second cavity  21  is disposed in the second waveguide body  20 , and a structure and a shape of the second cavity  21  are the same as those of the first cavity  11 . Specifically, in this implementation manner, the structure of the second waveguide body  20  is similar to that of the first waveguide body  10 . The second waveguide body  20  includes a second butt-joint face  23  and a second interface face  25  that extend along a length direction of the second waveguide body  20 , and the second butt-joint face  23  and the second interface face  25  are adjacent and perpendicular to each other. The second cavity  21  extends along the length direction of the second waveguide body  20 , and the length direction of the second waveguide body  20  is the propagation direction of the electromagnetic wave of the tunable filter in the present invention. The second cavity  21  extends inwards the second waveguide body  20  from the second butt-joint face  23 , and both ends of the second cavity  21  separately lead to the second interface face  25 . That is, a notch  252  is disposed at each of both ends of the second interface face  25 , and the two notches  252  are configured to enable an exterior of the second waveguide body  20  to communicate with the second cavity  21 . The second waveguide body  20  further includes a second end face  27  perpendicularly connected between the second butt-joint face  23  and the second interface face  25 . Projection of the second cavity  21  on the second interface face  25  is a rectangle. 
     The first waveguide body  10  is in butt joint with the second waveguide body  20 , as shown in  FIG. 1 , an input end P 1  and an output end P 2  are formed at both ends of a juncture of the first waveguide body  10  and the second waveguide body  20 , and the electromagnetic wave in the tunable filter is propagated from the input end P 1  to the output end P 2 . Specifically, the first butt-joint face  13  is opposite to the second butt-joint face  23 , and at the same time, the first cavity  11  is opposite to the second cavity  21 . After butt joint, the first interface face  15  and the second interface face  25  are coplaner, and the first end face  17  and the second end face  27  are also coplaner. In addition, the two notches  152  on the first interface face  15  are respectively in butt joint with the two notches  252  on the second interface face  25 . In this way, the input end P 1  and the output end P 2  are formed at the notches on the first interface face  15  and the second interface face  25 . 
     The metal plate  30  is sandwiched between the first waveguide body  10  and the second waveguide body  20 , that is, between the first butt-joint face  13  and the second butt-joint face  23 . Multiple windows  32  are disposed on the metal plate  30 , the multiple windows  32  are distributed along the propagation direction of the electromagnetic wave of the tunable filter, and the first cavity  11  and the second cavity  21  are in communication and are symmetrically distributed on both sides of the metal plate  30 . The metal plate  30  is sandwiched between the first cavity  11  and the second cavity  21 , to separate the first cavity  11  from the second cavity  21 . However, because the multiple windows  32  are disposed on the metal plate  30 , where the windows  32  may be, but not limited to, a rectangular structure, the first cavity  11  and the second cavity  21  are in communication with each other by using the multiple windows  32 . The metal plate  30  is in a rectangular sheet-like structure, a long edge of the metal plate  30  is an interface edge  34 , the multiple windows  32  are distributed in a middle position of two long edges of the metal plate  30  along a length direction of the metal plate  30 , and a notch  342  is disposed at each of both ends of the interface edge  34  of the metal plate  30 . After assembly, the notch  342  on the metal plate  30  is separately aligned with the notch  152  on the first waveguide body  10  and the notch  252  on the second waveguide body  20 . 
     The first waveguide body  10  and the second waveguide body  20  are fixed by using multiple screws, or the first waveguide body  10  and the second waveguide body  20  are permanently connected in a manner of mucilage glue or welding. A vibration absorbing washer may also be disposed between the first waveguide body  10  and the second waveguide body  20 . For example, the vibration absorbing washer is disposed at a joint of the first waveguide body  10  and the second waveguide body  20 . 
     The tuning piece  40  includes a dielectric pull-rod  42  and multiple metal sheets  44  connected to the dielectric pull-rod  42 . The dielectric pull-rod  42  traverses the first waveguide body  10 . The dielectric pull-rod  42  protrudes out of the first waveguide body  10  and is connected to the driving piece  50 . The multiple metal sheets  44  are disposed inside the first cavity  11 , and the multiple metal sheets  44  and the multiple windows  32  are distributed in a same manner and are disposed in a one-to-one correspondence. As shown in  FIG. 2  and  FIG. 3 , a quantity of the metal sheets  44  is eight, a quantity of the windows  32  is also eight, and both are distributed at regular intervals. The multiple metal sheets  44  are distributed on a same plane, and all the multiple metal sheets  44  are parallel to the metal plate  30 . Specifically, in this implementation manner, one end of the dielectric pull-rod  42  passes through the first positioning hole  16  of the first waveguide body  10 , and protrudes out of the first waveguide body  10 , and the other end of the dielectric pull-rod  42  is positioned inside the second positioning hole  18  of the first waveguide body  10 . The dielectric pull-rod  42  is in clearance fit with both the first positioning hole  16  and the second positioning hole  18 , so that the dielectric pull-rod  42  can move relative to the first waveguide body  10 . 
     The driving piece  50  drives the tuning piece  40  to move relative to the metal plate  30 , that is, to change a position relationship between the tuning piece  40  and the metal plate  30 , to adjust a frequency of the tunable filter. Specifically, in a process in which the driving piece  50  drives the dielectric pull-rod  42  to move, a position relationship between the metal sheets  44  and the corresponding windows  32  on the metal plate is changed, that is, the frequency of the tunable filter is changed. The multiple metal sheets  44  are disposed on the dielectric pull-rod  42  in a scattered manner, and an area of a single metal sheet  44  is small. Therefore, in an adjustment and functioning process, the metal sheets  44  have a relatively good shock resistance capability, and can ensure stability of working performance of the tunable filter. 
     According to the tunable filter provided in this embodiment of the present invention, process reliability is improved by designing a tuning piece  40  into an aggregate of a dielectric pull-rod  42  and multiple metal sheets  44  connected to the dielectric pull-rod  42 . Compared with an integral dielectric slice in the prior art, because a single body of the multiple metal sheets  44  has a small area, the metal sheets  44  are easy in manufacturing and have a good shock resistance capability, thereby ensuring stability of a frequency and performance of the tunable filter. 
     A connection structure between the multiple metal sheets  44  and the dielectric pull-rod  42  is not limited to one type. In an implementation manner of the present invention, the multiple metal sheets  44  are bonded to one side of the dielectric pull-rod  42  by using gel. In another implementation manner, multiple grooves are disposed on the dielectric pull-rod  42 , and the multiple metal sheets  44  are properly assembled with the multiple grooves respectively, to implement a fixed connection between the multiple metal sheets  44  and the dielectric pull-rod  42 , where the multiple metal sheets  44  are located on one side of the dielectric pull-rod  42 . In connection structures of the two implementation manners, the metal sheets  44  are located on one side of the dielectric pull-rod  42 . In another implementation manner of the present invention, multiple grooves are disposed on the dielectric pull-rod  42 , and the multiple metal sheets  44  respectively pass through the multiple grooves, so that each metal sheet  44  passes through the dielectric pull-rod  42 . In this implementation manner, the metal sheets  44  are located on both sides of the dielectric pull-rod  42 . Distribution of the metal sheets  44  on the both sides of the dielectric pull-rod  42  is not limited to one form. In this implementation manner, each metal sheet  44  is axisymmetrically distributed by using the dielectric pull-rod  42  as a central axis. In another implementation manner, a relationship between the metal sheets  44  and the dielectric pull-rod  42  may also be an asymmetric distribution manner, and a size of the metal sheets  44  protruding out of one side of the dielectric pull-rod  42  is less than a size of the metal sheets  44  protruding out of the other side of the dielectric pull-rod  42 . 
     Specifically, thicknesses of all the multiple metal sheets  44  are less than or equal to 1 mm, and all the multiple metal sheets  44  are in a rectangular sheet-like structure. The dielectric pull-rod  42  is in a slender cuboid shape or a slender cylinder shape. 
     The multiple windows  32  are distributed on the metal plate  30  at regular intervals. For example, the multiple windows  32  are distributed on the metal plate  30  at equal intervals. A rule for distributing the multiple windows  32  on the metal plate  30  is the same as a rule for distributing the multiple metal sheets  44  on the dielectric pull-rod  42 . 
     The driving piece  50  drives the dielectric pull-rod  42  to perform reciprocating motion along the propagation direction of the electromagnetic wave. Referring to  FIG. 1  and  FIG. 4 , the driving piece  50  includes a gear  52 , a stepper motor  54 , and a mounting bracket  56 . A gear rack  422  is disposed at one end of the dielectric pull-rod  42 , and the gear rack  422  and the gear  52  are used together, to implement power transmission between the driving piece  50  and the dielectric pull-rod  42 . The stepper motor  54  is configured to drive the gear  52  to rotate, and the gear  52  is disposed on an output shaft of the stepper motor  54 . The mounting bracket  56  is fixed at one end of the stepper motor  54  by using a screw, and the mounting bracket  56  is configured to permanently connect to the first waveguide body  10  and the second waveguide body  20 . In another implementation manner, linkage between the driving piece  50  and the dielectric pull-rod  42  may also be implemented by means of belt transmission or by using another linkage structure. The driving piece  50  may also be an air cylinder. 
     The foregoing descriptions are implementation manners of the present invention. It should be noted that a person of ordinary skill in the art may make certain improvements and polishing without departing from the principle of the present invention and the improvements and polishing shall fall within the protection scope of the present invention.