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CN-122026041-A - Compact cavity filter with transmission zero introduced in straight line mode

CN122026041ACN 122026041 ACN122026041 ACN 122026041ACN-122026041-A

Abstract

The invention discloses a compact cavity filter with transmission zeros introduced in an in-line mode, which comprises an electromagnetic resonant cavity, N-1 coupling control units and N frequency fine tuning units, wherein N is more than or equal to 2, the electromagnetic resonant cavity comprises a metal cavity and N resonant rods, the metal cavity is a closed cavity formed in a metal block, the inside of the metal cavity is linearly divided into N areas along the left-right direction, the N resonant rods are embedded in the N areas in a one-to-one correspondence mode, each resonant rod and the inner wall of the metal cavity in the area where the resonant rods are located are enclosed to form a resonant cavity unit, a coupling control unit is arranged between every two adjacent resonant cavity units, the N frequency fine tuning units are in one-to-one correspondence with the N resonant cavity units, a first interdigital capacitor structure is arranged between the top of each resonant rod and the inner top surface of the metal cavity, and a second interdigital capacitor structure is arranged between the front side of each resonant rod and the inner wall of the front side of the metal cavity.

Inventors

  • LIU BO
  • Zhong Shuomin

Assignees

  • 宁波大学

Dates

Publication Date
20260512
Application Date
20260213

Claims (7)

  1. 1. The compact cavity filter with the transmission zero introduced in the straight-line mode comprises an electromagnetic resonant cavity, N-1 coupling control units and N frequency fine tuning units, wherein N is more than or equal to 2, the electromagnetic resonant cavity comprises a metal cavity and N resonant rods, the metal cavity is a closed cavity formed in a metal block, the inside of the metal cavity is linearly divided into N areas along the left-right direction, the N resonant rods are embedded in the N areas in a one-to-one correspondence mode, each resonant rod and the inner wall of the metal cavity in the area where the resonant rod is located enclose to form a resonant cavity unit, one coupling control unit is arranged between every two adjacent resonant cavity units, the N frequency fine tuning units are in one-to-one correspondence with the N resonant cavity units, each frequency fine tuning unit is used for accurately calibrating the resonant frequency of the resonant cavity unit corresponding to the coupling control unit, and is characterized in that a first interdigital capacitor structure is arranged between the top of each resonant rod and the inner top surface of the metal cavity, a second interdigital capacitor structure is arranged between the front side of each resonant rod and the inner wall of the front side of the metal cavity, the N resonant rods are distributed along the left-right direction, the N frequency fine tuning units are used for achieving the fact that the distance between the N resonant cavity units and the adjacent resonant cavity units is different from the nearest to each resonant cavity unit, and the adjacent resonant cavity unit is used for achieving the signal transmission of the signal, and the signal transmission distance between the adjacent resonant cavity units is different from the adjacent resonant cavity units, and the resonant cavity units.
  2. 2. The compact cavity filter with transmission zero introduced in an in-line mode according to claim 1, wherein each resonant rod comprises a cuboid metal conductor and a cylindrical metal conductor which are coaxially stacked up and down, the width of the cuboid metal conductor in the front-back direction and the length of the cuboid metal conductor in the left-right direction are both larger than the diameter of the cylindrical metal conductor, the bottom end of the cylindrical metal conductor is abutted and fixed with the inner bottom surface of the metal cavity, and a preset interval is reserved between the top end of the cuboid metal conductor and the inner top surface of the metal cavity.
  3. 3. The compact cavity filter with transmission zero introduced in an in-line mode according to claim 2, wherein a first cylindrical hole and a first annular hole are formed in the top end of a cuboid metal conductor of each resonant rod, the cuboid metal conductor, the first cylindrical hole and the first annular hole are coaxially arranged, the first annular hole is coaxially sleeved outside the first cylindrical hole, a first annular body which keeps a preset gap with the side wall of the first annular hole is arranged in the first annular hole, the top end of the first annular body is fixed on the inner top surface of the metal cavity, and the cuboid metal conductor, the first annular hole and the first annular body jointly form the first interdigital capacitor structure.
  4. 4. The compact cavity filter with the transmission zero introduced in the straight-line mode according to claim 3, wherein a second cylindrical hole and a second annular hole which are recessed backwards are formed in the front side of a cuboid metal conductor of each resonant rod, the second cylindrical hole and the second annular hole are coaxially arranged, the second annular hole is coaxially sleeved outside the second cylindrical hole, a second annular body which keeps a preset gap with the side wall of the second annular hole is arranged in the second annular hole, the second annular body and the second annular hole are coaxially arranged, the front end of the second annular body is fixed on the inner wall of the front side of the metal cavity, and the cuboid metal conductor, the second annular hole and the second annular body jointly form the second interdigital capacitor structure.
  5. 5. The compact cavity filter introducing transmission zeros in an in-line form according to claim 3, wherein each of the frequency trimming units comprises two tuning screws, a first tuning screw and a second tuning screw, respectively, the first tuning screw vertically penetrates through an inner top surface of the metal cavity and an outer top surface of the metal block by screw-fitting, the second tuning screw vertically penetrates through a front inner wall of the metal cavity and an outer front wall of the metal block by screw-fitting, corresponding one of the frequency trimming units and one of the resonant cavity units, the first tuning screw is coaxial with the first cylindrical hole, a bottom end thereof extends into and does not contact with a side wall of the first cylindrical hole, the second tuning screw is coaxial with the second cylindrical hole, a bottom end thereof extends into and does not contact with a side wall of the second cylindrical hole, and a resonant frequency of the resonant cavity unit is precisely calibrated by rotating the first tuning screw and the second tuning screw, thereby changing a relative position of the first tuning screw and the first cylindrical hole and a relative position of the second screw and the second cylindrical hole.
  6. 6. The compact cavity filter with the transmission zero introduced in the straight-line mode according to claim 2 is characterized in that each coupling control unit comprises a coupling screw rod, N-1 mounting holes penetrating up and down are formed from the inner bottom surface of the metal cavity to the outer bottom surface of the metal block, the N-1 mounting holes are linearly arranged in the left-right direction and located right below each two adjacent areas in a one-to-one correspondence mode, the N-1 coupling screw rods are embedded in the N-1 mounting holes in a one-to-one correspondence mode through threaded fit, the top ends of the N-1 coupling screw rods extend to between the two adjacent resonant cavity units, and the diameter of each coupling screw rod included by each coupling control unit is larger than that of a cylindrical metal conductor of each resonant rod.
  7. 7. The compact cavity filter introducing transmission zeroes in-line according to claim 6, wherein the N-1 coupling control units comprise coupling screws of equal diameters.

Description

Compact cavity filter with transmission zero introduced in straight line mode Technical Field The invention relates to a cavity filter, in particular to a compact cavity filter with transmission zero introduced in an in-line mode. Background The filter is a typical frequency selection device, and can effectively suppress unwanted signals, and play roles in selecting useful signals, attenuating noise, and filtering interference. At present, the market demand of the low-cost filter is continuously increased due to the increasingly strong popularization of green energy and the increasing demand of cost control, and meanwhile, the rapid development of mobile communication promotes the microwave radio frequency device to evolve towards a compact direction, and the trend brings new requirements to the structural design of the filter. The cavity filter is one of the common filter types, has the advantages of large power capacity and adaptation to high-power radio frequency scenes, and has obvious application value in communication systems such as base stations and the like by virtue of high Q value, low insertion loss and excellent frequency selectivity, and particularly has the performance far exceeding microstrip filter and the like in high-frequency scenes. The traditional cavity filter is designed based on the electromagnetic resonance characteristics of a metal resonant cavity, and mainly comprises an electromagnetic resonant cavity, N frequency fine tuning units and N-1 coupling control units, wherein N is equal to the filtering order of the cavity filter and is more than or equal to 2. The electromagnetic resonant cavity comprises a metal cavity and N resonant rods, wherein the metal cavity is a closed cavity formed in the metal block, the inside of the metal cavity is linearly divided into N areas along the left-right direction, the N resonant rods are arranged in the N areas in a one-to-one correspondence mode, each resonant rod and the inner wall of the metal cavity in the area where the resonant rod is located enclose to form a resonant cavity unit, and the N resonant rods and the metal cavity form N resonant cavity units. The N frequency fine tuning units are in one-to-one correspondence with the N resonant cavity units, and each frequency fine tuning unit is used for accurately calibrating the resonant frequency of the resonant cavity unit corresponding to the frequency fine tuning unit so as to compensate frequency offset caused by processing errors. And a coupling control unit is arranged between every two adjacent resonant cavity units, and each coupling control unit is used as an electromagnetic energy transmission channel and is used for realizing electromagnetic energy coupling between the two adjacent resonant cavity units. When signals are transmitted in the electromagnetic resonant cavity, electromagnetic fields of two adjacent resonant cavity units interact to cause coupling splitting of respective resonant modes, wherein a single resonant peak of an original single resonant cavity unit is split into a plurality of resonant peaks, and after N resonant cavity units are subjected to multistage coupling through N-1 coupling control units, the split resonant peaks are mutually overlapped and compensated to finally form a continuous and flat passband. In a traditional cavity filter, the physical size of a metal cavity determines the resonant frequency of the cavity filter, N resonant cavity units have their own specific resonant frequency points, and when a mixed signal containing a plurality of signals with different frequencies enters the cavity filter, a signal matched with the passband of the cavity filter can pass through the cavity filter, and a signal which is not matched with the passband of the cavity filter can be filtered by the cavity filter. The resonant rod is the main component of the cavity filter, and its size directly determines the size of the whole cavity filter. In conventional cavity filters, the resonant rods are typically implemented using upright cylindrical metal conductors. The resonant frequency f of each resonant cavity unit is determined by the equivalent inductance and the equivalent capacitance of the resonant cavity unit: Where L is the equivalent inductance of the resonant cavity unit, C is the equivalent capacitance of the resonant cavity unit, ,Is the vacuum dielectric constant, A is the facing area of the outer surface of the resonant rod and the inner side wall of the metal cavity, and d is the distance between the outer surface of the resonant rod and the inner side wall of the metal cavity.,Is the vacuum permeability, h is the height of the resonant rod, and r is the radius of the resonant rod. From the above, it can be seen that if C is larger, A is larger and d is smaller, if L is larger, h is larger and r is smaller. In each resonant cavity unit, only the bottom of the resonant rod is abutted against the inner bottom surface of the metal cavity, the top