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

Abstract

The invention discloses a compact cavity filter introducing a transmission zero point in a straight-line mode, which comprises an electromagnetic resonant cavity, N-1 coupling control units and N frequency fine tuning units, and N is greater than or equal to 2; the electromagnetic resonant cavity comprises a metal cavity and N resonant rods, the metal cavity is a closed inner cavity formed in a metal block, the interior of the metal cavity is linearly divided into N areas in the left-right direction, the N resonant rods are embedded in the N areas in a one-to-one correspondence mode, and each resonant rod and the inner wall of the metal cavity in the area where the resonant rod is located define 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; a first interdigital capacitor structure is arranged between the top of each resonance rod and the inner top surface of the metal cavity, and a second interdigital capacitor structure is arranged between the front side surface of each resonance rod and the inner wall of the front side of the metal cavity; the invention has the advantages of compact structure and small overall size.

Description

Technical Field

[0001] This invention relates to cavity filters, and more particularly to a compact cavity filter with a straight-line configuration that introduces transmission zeros. Background Technology

[0002] Filters are typical frequency selective devices that effectively suppress unwanted signals while selecting useful signals, attenuating noise, and filtering out interference. Currently, the demand for green energy promotion and cost control is increasingly strong, leading to a continuous growth in the market demand for low-cost filters. Simultaneously, the rapid development of mobile communications is driving the evolution of microwave radio frequency devices towards compact designs, a trend that places new requirements on filter structural design.

[0003] Cavity filters, as one of the commonly used filter types, have the advantages of large power capacity and suitability for high-power radio frequency scenarios. With their high Q value, low insertion loss and excellent frequency selectivity, they have significant application value in communication systems such as base stations, especially in high-frequency scenarios where their performance far exceeds that of similar products such as microstrip filters.

[0004] Traditional cavity filters are designed based on the electromagnetic resonance characteristics of metal resonant cavities. They mainly consist of an electromagnetic resonant cavity, N frequency fine-tuning units, and N-1 coupling control units, where N equals the filter order of the cavity filter and is greater than or equal to 2. The electromagnetic resonant cavity comprises a metal cavity and N resonant rods. The metal cavity is a closed inner cavity created within a metal block, linearly divided into N regions along the left-right direction. The N resonant rods are correspondingly positioned in each of these regions, with each rod and its corresponding region's inner wall forming a cavity unit. The N resonant rods and the metal cavity together form N cavity units. The N frequency fine-tuning units correspond one-to-one with the N cavity units, each used to precisely calibrate the resonant frequency of its corresponding cavity unit to compensate for frequency shifts caused by manufacturing errors. A coupling control unit is positioned between every two adjacent cavity units, serving as an electromagnetic energy transfer channel to achieve electromagnetic energy coupling between adjacent cavity units. When a signal is transmitted in an electromagnetic resonant cavity, the electromagnetic fields of two adjacent resonant cavity units will interact, causing their respective resonant modes to couple and split: the single resonant peak of a single resonant cavity unit will split into multiple resonant peaks; after N resonant cavity units are coupled through N-1 coupling control units, the split resonant peaks superimpose and compensate for each other, eventually forming a continuous and flat passband.

[0005] In traditional cavity filters, the physical dimensions of the metal cavity determine the resonant frequency of the cavity filter. N resonant cavity units have their own specific resonant frequency points. When a mixed signal containing multiple signals of different frequencies enters the cavity filter, the signal that matches the passband of the cavity filter can pass through the cavity filter, while the signal that does not match is filtered out by the cavity filter.

[0006] The resonant rod is a key component of a cavity filter, and its size directly determines the overall size of the filter. In traditional cavity filters, the resonant rod is typically implemented using a vertical cylindrical metal conductor. The resonant frequency f of each cavity element is determined by its equivalent inductance and equivalent capacitance. Where L is the equivalent inductance of the resonant cavity unit, and C is the equivalent capacitance of the resonant cavity unit. , is the vacuum dielectric constant, A is the area of ​​the outer surface of the resonant rod and the inner wall of the metal cavity facing each other, and d is the distance between the outer surface of the resonant rod and the inner wall of the metal cavity. , Where C 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 large, then A is large and d is small; if L is large, then h is large and r is small. In each resonant cavity unit, the resonant rod only contacts the bottom surface of the metal cavity; its top surface does not contact the top surface of the metal cavity, and its outer surface does not contact the inner wall of the metal cavity. The longitudinal equivalent capacitance of the resonant cavity unit is formed between the top of the resonant rod and the top surface of the metal cavity; the transverse equivalent capacitance of the resonant cavity unit is formed between the outer surface of the resonant rod and the inner wall of the metal cavity. The transverse and longitudinal equivalent capacitances of the resonant cavity unit constitute the equivalent capacitance of the entire resonant cavity unit.

[0007] In traditional cavity filters, designing a low-frequency cavity filter requires each resonant cavity unit to have a low resonant frequency, necessitating large values ​​for both C and L. However, a large C leads to a large A, which in turn results in a large r, causing L to decrease. Therefore, currently, L is increased by increasing h. Consequently, in traditional cavity filters, the resonant rod has a large height and diameter, resulting in a large overall size of the cavity filter. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a compact cavity filter with a compact structure and small overall size, which introduces a transmission zero in a straight-line form.

[0009] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a compact cavity filter with a straight-lined zero-point transmission, comprising an electromagnetic resonant cavity, N-1 coupling control units, and N frequency fine-tuning units, where N≥2; the electromagnetic resonant cavity comprises a metal cavity and N resonant rods, wherein the metal cavity is a closed inner cavity opened inside a metal block, and its interior is linearly divided into N regions along the left-right direction, with the N resonant rods embedded one-to-one in the N regions, and each resonant rod and the inner wall of the metal cavity in its region forming a resonant cavity unit; one coupling control unit is arranged between every two adjacent resonant cavity units, and the N frequency fine-tuning units correspond one-to-one with the N resonant cavity units. Each frequency fine-tuning unit is used to precisely calibrate the resonant frequency of its corresponding resonant cavity unit; a first interdigitated capacitor structure is provided between the top of each resonant rod and the top surface of the metal cavity, and a second interdigitated capacitor structure is provided between the front side of each resonant rod and the front inner wall of the metal cavity. N resonant rods are linearly distributed along the left and right direction. N-1 coupling control units are used to realize electromagnetic energy coupling between every two adjacent resonant cavity units and the two closest non-adjacent resonant cavity units in the N resonant cavity units, and to generate a 180° phase difference between the signal transmitted between the two adjacent resonant cavity units and the signal transmitted between the two closest non-adjacent resonant cavity units.

[0010] Compared with the prior art, the advantages of the present invention are as follows: By setting a first interdigitated capacitor structure between the top of each resonant rod and the top surface of the metal cavity, and setting a second interdigitated capacitor structure between the front side of each resonant rod and the front inner wall of the metal cavity, the first interdigitated capacitor structure can increase the longitudinal equivalent capacitance of the resonant cavity unit, and the second interdigitated capacitor structure can increase the lateral equivalent capacitance of the resonant cavity unit, thereby increasing the equivalent capacitance of the resonant cavity unit. At the same resonant frequency, the resonant cavity unit can achieve a larger equivalent capacitance by using a smaller resonant rod and a smaller facing area of ​​the inner wall of the metal cavity. The resonant rod can also have a smaller height. In addition, N resonant rods are linearly distributed along the left and right directions, and N-1 coupling control units are used. This invention enables electromagnetic energy coupling between every two adjacent resonant cavity units and between the two nearest non-adjacent resonant cavity units in N resonant cavity units. This results in a 180° phase difference between the signals transmitted between the two adjacent resonant cavity units and the signals transmitted between the two nearest non-adjacent resonant cavity units, thereby generating transmission zeros at multiple preset frequency points. Without increasing the order of the compact cavity filter (without increasing the volume or insertion loss), this invention significantly improves the frequency selectivity of the compact cavity filter and achieves flexible stopband suppression. Therefore, under the same resonant frequency conditions, this invention can significantly reduce the height of the resonant rod and the outer dimensions, resulting in a compact structure and a small overall size.

[0011] Furthermore, each resonant rod includes a cuboid metal conductor and a cylindrical metal conductor stacked coaxially on top of each other. The width of the cuboid metal conductor in the front-to-back direction and the length in the left-to-right direction are both greater than the diameter of the cylindrical metal conductor. The bottom end of the cylindrical metal conductor is fixed to the inner bottom surface of the metal cavity. There is a preset distance between the top end of the cuboid metal conductor and the inner top surface of the metal cavity.

[0012] Furthermore, each resonant rod has a cuboid metal conductor with a downwardly recessed first cylindrical hole and a first annular hole at its top. The cuboid metal conductor, the first cylindrical hole, and the first annular hole are coaxially arranged, and the first annular hole is coaxially fitted outside the first cylindrical hole. A first annular body with a preset gap between it and its sidewall is arranged inside the first annular hole. The top of the first annular body is fixed to the inner top surface of the metal cavity. The cuboid metal conductor, the first annular hole, and the first annular body together constitute the first interdigital capacitor structure.

[0013] Furthermore, each resonant rod has a rearwardly recessed second cylindrical hole and a second annular hole on its front side of the cuboid metal conductor. The second cylindrical hole and the second annular hole are coaxially arranged, with the second annular hole coaxially fitted outside the second cylindrical hole. A second annular body is arranged inside the second annular hole, maintaining a preset gap with its sidewall. The second annular body is coaxially arranged with the second annular hole. The front end of the second annular body is fixed to the front inner wall of the metal cavity. The cuboid metal conductor, the second annular hole, and the second annular body together constitute the second interdigital capacitor structure.

[0014] Furthermore, each frequency fine-tuning unit includes two tuning screws, namely a first tuning screw and a second tuning screw. The first tuning screw penetrates vertically through the inner top surface of the metal cavity and the outer top surface of the metal block via a threaded connection. The second tuning screw penetrates vertically through the front inner wall of the metal cavity and the outer front wall of the metal block via a threaded connection. In a corresponding frequency fine-tuning unit and a resonant cavity unit, the first tuning screw is coaxial with the first cylindrical hole, and its bottom end extends into the first cylindrical hole without contacting the side wall of the first cylindrical hole. The second tuning screw is coaxial with the second cylindrical hole, and its bottom end extends into the second cylindrical hole without contacting the side wall of the second cylindrical hole. By rotating the first tuning screw and the second tuning screw, the relative positions of the first tuning screw and the first cylindrical hole and the second tuning screw and the second cylindrical hole are changed, thereby accurately calibrating the resonant frequency of the resonant cavity unit.

[0015] Furthermore, each coupling control unit includes a coupling screw; N-1 mounting holes 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 are located directly below each of two adjacent regions; the N-1 coupling screws are threaded into the N-1 mounting holes, and their top ends extend to the space between two adjacent resonant cavity units; the diameter of the coupling screw included in each coupling control unit is larger than the diameter of the cylindrical metal conductor of all the resonant rods.

[0016] Furthermore, the coupling screws in the N-1 coupling control units all have the same diameter. Attached Figure Description

[0017] Figure 1 A perspective view of the compact cavity filter with a transmission zero introduced in the straight-line configuration of the present invention; Figure 2 Exploded view of the compact cavity filter with a transmission zero introduced in the straight-line configuration of the present invention; Figure 3 A cross-sectional view of the compact cavity filter with a transmission zero introduced in the straight-line configuration of the present invention; Figure 4 A structural diagram of the resonant rod unit of the compact cavity filter with a transmission zero introduced in a straight-line configuration according to the present invention; Figure 5 An exploded view of the resonant cavity unit of the compact cavity filter with a transmission zero introduced in a straight-line configuration according to the present invention; Figure 6 Exploded view of the metal cavity of the compact cavity filter with a transmission zero introduced in the straight-line configuration of the present invention; Figure 7 A structural diagram of the front cover plate of the compact cavity filter with a transmission zero point introduced in the straight-line configuration of the present invention; Figure 8 A structural diagram of the resonant rod, tuning screw, and coupling screw of the compact cavity filter with a straight-line configuration that introduces a transmission zero point according to the present invention; Figure 9 Simulation results of the compact cavity filter with a transmission zero introduced in the straight-line form of the present invention are shown. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0019] Example 1: As Figure 1 Figure 2As shown, a compact cavity filter with a straight-lined zero-point transmission design includes an electromagnetic resonant cavity 1, N-1 coupling control units 2, and N frequency fine-tuning units 3, where N=4. The electromagnetic resonant cavity 1 includes a metal cavity 4 and N resonant rods 5. The metal cavity 4 is a closed cavity opened inside a metal block, and its interior is linearly divided into N regions along the left-right direction. The N resonant rods 5 are embedded in the N regions one-to-one, and each resonant rod 5 and the inner wall of the metal cavity 4 in its region constitute a resonant cavity unit. A coupling control unit 2 is set between every two adjacent resonant cavity units. N frequency fine-tuning units 3 correspond one-to-one with N resonant cavity units. Each frequency fine-tuning unit 3 is used to precisely calibrate the resonant frequency of its corresponding resonant cavity unit. A first interdigital capacitor structure is provided between the top of each resonant rod 5 and the inner top surface of the metal cavity 4, and a second interdigital capacitor structure is provided between the front side of each resonant rod 5 and the front inner wall of the metal cavity 4. The N resonant rods 5 are linearly distributed along the left and right directions. N-1 coupling control units 2 are used to realize electromagnetic energy coupling between every two adjacent resonant cavity units and the two closest non-adjacent resonant cavity units in the N resonant cavity units, and to generate a 180° phase difference between the signal transmitted between the two adjacent resonant cavity units and the signal transmitted between the two closest non-adjacent resonant cavity units.

[0020] The compact cavity filter with a transmission zero introduced in the straight-line configuration of this embodiment is a fourth-order coaxial cavity filter, consisting of four independent resonant cavity units cascaded sequentially. Each resonant cavity unit generates electromagnetic resonance. When a signal enters the electromagnetic resonant cavity 1 through the RF coaxial connector 9, the electromagnetic fields of adjacent resonant cavity units interact during transmission, causing their respective resonant modes to couple and split: the single resonant peak of a single resonant cavity unit splits into multiple resonant peaks; after multi-stage coupling of the four resonant cavity units through three coupling screws, the split resonant peaks superimpose and compensate for each other, ultimately forming a continuous and flat passband.

[0021] In this embodiment, a first interdigitated capacitor structure is provided between the top of each resonant rod 5 and the inner top surface of the metal cavity 4, and a second interdigitated capacitor structure is provided between the front side of each resonant rod 5 and the front inner wall of the metal cavity 4. The first interdigitated capacitor structure can increase the longitudinal equivalent capacitance of the resonant cavity unit, and the second interdigitated capacitor structure can increase the lateral equivalent capacitance of the resonant cavity unit, thereby increasing the equivalent capacitance of the resonant cavity unit. Thus, at the same resonant frequency, the resonant cavity unit can achieve a larger equivalent capacitance by using a smaller area of ​​the resonant rod 5 and the inner wall of the metal cavity 4. The resonant rod 5 can also have a smaller height. Therefore, under the same resonant frequency conditions, the present invention can significantly reduce the height and outer dimensions of the resonant rod 5, resulting in a compact structure and a smaller overall size.

[0022] Example 2: This example is basically the same as Example 1, except that: in this example, as Figures 2 to 7 As shown, each resonant rod 5 includes a cuboid metal conductor 51 and a cylindrical metal conductor 52 stacked coaxially. The width of the cuboid metal conductor 51 in the front-to-back direction and the length in the left-to-right direction are both greater than the diameter of the cylindrical metal conductor 52. The bottom end of the cylindrical metal conductor 52 is fixed to the inner bottom surface of the metal cavity 4. There is a preset distance between the top end of the cuboid metal conductor 51 and the inner top surface of the metal cavity 4.

[0023] Example 3: This example is basically the same as Example 2, except that: in this example, as Figures 2 to 7 As shown, each resonant rod 5 has a cuboid metal conductor 51 with a downwardly recessed first cylindrical hole 53 and a first annular hole 54 at its top. The cuboid metal conductor 51, the first cylindrical hole 53, and the first annular hole 54 are coaxially arranged, and the first annular hole 54 is coaxially sleeved on the outside of the first cylindrical hole 53. A first annular body 55 with a preset gap between it and its sidewall is provided inside the first annular hole 54. The top of the first annular body 55 is fixed on the inner top surface of the metal cavity 4. The cuboid metal conductor 51, the first annular hole 54, and the first annular body 55 together constitute the first interdigital capacitor structure.

[0024] In this embodiment, the top of the metal block has an upper opening identical to the closed inner cavity, and an upper cover plate 6 is provided to close the upper opening. The top end of the first annular body 55 is fixed to the upper cover plate 6. Since the upper cover plate 6 is detachable, the first annular body 55 can be precisely positioned during processing, thereby ensuring the vertical installation accuracy of the first annular body 55 and the first annular hole 54 while reducing the processing and installation difficulty.

[0025] In this embodiment, the specific dimensions of the resonant rod 5 are determined according to the resonant point parameters to be achieved during implementation.

[0026] Example 4: This example is basically the same as Example 3, except that: in this example, as Figures 2 to 8 As shown, each resonant rod 5 has a rearwardly recessed second cylindrical hole 56 and a second annular hole 57 on the front side of its cuboid metal conductor 51. The second cylindrical hole 56 and the second annular hole 57 are coaxially arranged. The second annular hole 57 is coaxially sleeved on the outside of the second cylindrical hole 56. A second annular body 58 is arranged inside the second annular hole 57, maintaining a preset gap with its sidewall. The second annular body 58 is coaxially arranged with the second annular hole 57. The front end of the second annular body 58 is fixed on the front inner wall of the metal cavity 4. The cuboid metal conductor 51, the second annular hole 57 and the second annular body 58 together constitute the second interdigital capacitor structure.

[0027] In this embodiment, the metal block has a front opening identical to the closed inner cavity, and a front cover plate 7 is provided at the front opening to close it. The front end of the second annular body 58 is fixed to the front cover plate 7. Since the front cover plate 7 is detachable, the second annular body 58 can be precisely positioned during processing, thereby ensuring the front-to-back installation accuracy of the second annular body 58 and the second annular hole 57, while reducing the processing and installation difficulties.

[0028] Example 5: This example is basically the same as Example 4, except that: in this example, as Figures 2 to 7 As shown, each frequency fine-tuning unit 3 includes two tuning screws, namely a first tuning screw 31 and a second tuning screw 32. The first tuning screw 31 penetrates vertically through the inner top surface of the metal cavity 4 and the outer top surface of the metal block via a threaded connection. The second tuning screw 32 penetrates vertically through the front inner wall of the metal cavity 4 and the outer front wall of the metal block via a threaded connection. In a corresponding frequency fine-tuning unit 3 and a resonant cavity unit, the first tuning screw 31 is coaxial with the first cylindrical hole 53, and its bottom... The first tuning screw 31 extends into the first cylindrical hole 53 without contacting the side wall of the first cylindrical hole 53; the second tuning screw 32 is coaxial with the second cylindrical hole 56, and its bottom end extends into the second cylindrical hole 56 without contacting the side wall of the second cylindrical hole 56; by rotating the first tuning screw 31 and the second tuning screw 32, the relative positions of the first tuning screw 31 and the first cylindrical hole 53 and the second tuning screw 32 and the second cylindrical hole 56 are changed, thereby accurately calibrating the resonant frequency of the resonant cavity unit.

[0029] In this embodiment, the tuning screw in each resonant cavity unit adjusts the equivalent electrical length of the resonant rod 5 of that resonant cavity unit by changing the length of the screw extending into the resonant cavity unit, thereby accurately calibrating the resonant frequency of a single resonant cavity unit and ensuring that the resonant frequencies of the four resonant cavity units are precisely matched to the target passband.

[0030] Example 6: This example is basically the same as Example 5, except that: in this example, as Figures 2 to 7 As shown, each coupling control unit 2 includes a coupling screw; N-1 mounting holes 8 are provided from the inner bottom surface of the metal cavity 4 to the outer bottom surface of the metal block, and the N-1 mounting holes 8 are arranged linearly in the left-right direction and are located directly below each of two adjacent regions; the N-1 coupling screws are threaded into the N-1 mounting holes 8, and their top ends extend to the space between two adjacent resonant cavity units; the diameters of the coupling screws included in the N-1 coupling control units are all equal and larger than the diameter of the cylindrical metal conductors 52 of all the resonant rods 5.

[0031] In this embodiment, the electromagnetic coupling strength between two adjacent resonant cavity units is adjusted by turning the top extension height of each coupling screw. When the top extension height of two adjacent coupling screws is adjusted, the electromagnetic coupling strength between the resonant cavity unit located to the left of the preceding coupling screw and adjacent to it, and the resonant cavity unit located to the right of the following coupling screw and adjacent to it, is adjusted synchronously. In this embodiment, by placing the coupling control unit 2 at the bottom of the entire cavity filter for electromagnetic energy coupling and transmission, the lateral distance between the resonant rods 5 is reduced, thereby reducing the lateral size of the cavity filter.

[0032] In this embodiment, the coupling screw allows for flexible control of the electromagnetic energy coupling between resonant cavity units, achieving a steep passband transition and excellent out-of-band suppression. The tuning screw allows for precise calibration of the resonant frequency of each resonant cavity unit after assembly, effectively compensating for manufacturing and assembly errors and improving the frequency accuracy and consistency of the cavity filter. The synergistic cooperation of the coupling screw and the tuning screw not only gives the cavity filter structure superior frequency selection characteristics but also endows the bulk filter with greater tuning flexibility and performance stability, enabling efficient screening of target frequency band signals and suppression of out-of-band interference in complex electromagnetic environments.

[0033] The compact cavity filter of this invention, which introduces a transmission zero in a straight-line configuration, generates a transmission zero by controlling electromagnetic energy coupling between the nearest resonant rod 5 on the left and the nearest resonant rod 5 on the right (i.e., the two closest non-adjacent resonant rods 5) in each of the N-1 coupling control units 2, which are grouped into a coupling unit group. Specifically, the first and third resonant rods 5 are electromagnetically coupled through the first and second coupling control units 2, resulting in a -90° (90° counterclockwise) phase shift in the signal transmitted there. The first resonant rod 5 is then coupled through the second and third resonant rods 5, resulting in a -270° (270° counterclockwise) phase shift in the signal transmitted there. This means the signals transmitted through these two paths have a 180° phase difference, leading to a linear insertion loss of 0 at the corresponding frequency, which is reflected as a dip in the S-parameter curve of the compact cavity filter at that frequency. The second and fourth resonant rods 5 are electromagnetically coupled through the second and third coupling control units 2, resulting in a -90° phase shift in the signal transmitted to them. The second resonant rod 5 is coupled through the third resonant rod 5 and then through the fourth resonant rod 5, resulting in a -270° phase shift in the signal transmitted to them. That is, the signals transmitted through these two paths have a 180° phase difference, which will result in a linear insertion loss of 0 at the corresponding frequency point, thus manifesting as a dip at that frequency point in the S-parameter curve of the compact cavity filter. Similarly, the (N-2)th resonant rod 5 and the Nth resonant rod 5 are electromagnetically coupled through the (N-2)th coupling screw 2 and the (N-1)th coupling screw 2 in a non-adjacent resonant path, causing a -90° phase shift in the signal transmitted there. The (N-2)th resonant rod 5 is then coupled through the (N-1)th resonant rod 5 and then through the Nth resonant rod 5 in an adjacent resonant path, causing a -270° phase shift in the signal transmitted there. The signals transmitted through these two paths have a 180° phase difference, generating a transmission zero at the corresponding frequency. Therefore, by linearly arranging N resonant rods 5 (i.e., in a straight line) and cooperating with N-1 coupling control units 2, this invention can generate transmission zeros at multiple preset frequency points, thereby significantly improving the frequency selectivity of the compact cavity filter without increasing the order of the compact cavity filter (without increasing the size or insertion loss) and achieving flexible stopband suppression.

[0034] To verify the performance of the compact cavity filter with a straight-lined transmission zero introduced by the present invention, simulation was performed on the compact cavity filter with a straight-lined transmission zero introduced by the present invention, and the simulation results are as follows. Figure 9As shown. The simulation parameters are set as follows: N=4. The four resonant rods 5 are named from left to right as the 1st resonant rod 5 to the 4th resonant rod 5, and the center distance between any two adjacent resonant rods 5 is 17.6mm. The parameters of the first resonant rod 5 and the fourth resonant rod 5 are as follows: the length (along the left-right direction), width (along the front-back direction), and height (along the up-down direction) of the cuboid metal conductor 51 are 16mm, 16mm, and 17.4mm, respectively; the radius and height of the cylindrical metal conductor 52 are 2mm and 6.5mm, respectively; the inner diameter, outer diameter, and height of the first annular hole 54 are 4.1mm, 6.5mm, and 7mm, respectively; the radius and height of the first cylindrical hole 53 are 2.3mm and 4mm, respectively; the inner diameter, outer diameter, and height of the first annular body 55 are 4.9mm, 5.7mm, and 7mm, respectively; the inner diameter, outer diameter, and height of the second annular hole 57 are 2mm, 3.5mm, and 14mm, respectively; the radius and height of the second cylindrical hole 56 are 1.5mm and 11mm, respectively; and the inner diameter, outer diameter, and height of the second annular body 58 are 4.9mm, 5.7mm, and 7mm, respectively. The parameters of the second and third resonant rods 5 are as follows: the length, width, and height of the cuboid metal conductor 51 are 16mm, 16mm, and 17.8mm, respectively; the radius and height of the cylindrical metal conductor 52 are 2mm and 6mm, respectively; the inner diameter, outer diameter, and height of the first annular hole 54 are 4.1mm, 6.5mm, and 7mm, respectively; the radius and height of the first cylindrical hole 53 are 2.3mm and 4mm, respectively; the inner diameter, outer diameter, and height of the first annular body 55 are 2.5mm, 3mm, and 14.9mm, respectively; the inner diameter, outer diameter, and height of the second annular hole 57 are 2mm, 3.5mm, and 14mm, respectively; the radius and height of the second cylindrical hole 56 are 1.5mm and 11mm, respectively; and the inner diameter, outer diameter, and height of the second annular body 58 are 2.5mm, 3mm, and 14.9mm, respectively. In each frequency fine-tuning unit 3, the first tuning screw 31 has a radius of 0.8 mm and a height of 1.5 mm, and the second tuning screw 32 has a radius of 0.8 mm and a height of 2.5 mm. The three coupling screws are referred to as the first to third coupling screws from left to right. All three coupling screws have a radius of 4 mm, a height of 5 mm for the first coupling screw, a height of 3.1 mm for the second coupling screw, and a height of 5 mm for the third coupling screw. The center distance between each coupling screw and its adjacent resonant rod 5 is 8.8 mm.

[0035] Since N=4, meaning there are 4 resonant rods 5 and 3 coupling control units 2, the first resonant rod 5 and the third resonant rod 5 are electromagnetically coupled through the first coupling control unit 2 and the second coupling control unit 2, generating the first transmission zero point, as shown below. Figure 9 As shown in Figure A; the second resonant rod 5 and the fourth resonant rod 5 are electromagnetically coupled through the second coupling control unit 2 and the third coupling control unit 2, generating the second transmission zero point, as shown in Figure A. Figure 9 As shown in B.

[0036] analyze Figure 9 It can be seen that the passband of the compact cavity filter with a straight-line transmission zero introduced in this invention is 663~698MHz. Within the passband, the return loss of the compact cavity filter with a straight-line transmission zero introduced in this invention is less than -20dB, and the insertion loss is close to 0dB. This indicates that the reflection of the input signal is very small, and input signals with frequencies within the passband can enter the compact cavity filter with a straight-line transmission zero introduced in this invention and be effectively transmitted with good transmission efficiency. Outside the passband, the return loss of the compact cavity filter with a straight-line transmission zero introduced in this invention is close to 0dB, indicating that most input signals are reflected and cannot enter the compact cavity filter with a straight-line transmission zero introduced in this invention. At 563MHz outside the passband, the out-of-band rejection of the compact cavity filter with a straight-line transmission zero introduced in this invention is greater than 40dB. At 798MHz outside the passband, the out-of-band rejection of the compact cavity filter with a straight-line transmission zero introduced in this invention is greater than 80dB. The two transmission zeros A and B outside the passband correspond to frequencies of 746MHz and 816MHz, respectively. According to the above analysis, the side with the transmission zero at 100MHz outside the passband has stronger out-of-band suppression than the side without the transmission zero.

Claims

1. A compact cavity filter with a straight-lined zero-point transmission design, comprising an electromagnetic resonant cavity, N-1 coupling control units, and N frequency fine-tuning units, where N ≥ 2; the electromagnetic resonant cavity comprises a metal cavity and N resonant rods, wherein the metal cavity is a closed inner cavity opened inside a metal block, and its interior is linearly divided into N regions along the left-right direction, with the N resonant rods embedded one-to-one in the N regions, each resonant rod and the inner wall of the metal cavity in its region forming a resonant cavity unit; a coupling control unit is provided between every two adjacent resonant cavity units, and the N frequency fine-tuning units correspond one-to-one with the N resonant cavity units, each frequency fine-tuning unit being used to precisely calibrate the resonant frequency of its corresponding resonant cavity unit; characterized in that... A first interdigitated capacitor structure is provided between the top of each resonant rod and the top surface of the metal cavity, and a second interdigitated capacitor structure is provided between the front side of each resonant rod and the front inner wall of the metal cavity. N resonant rods are linearly distributed in the left-right direction. N-1 coupling control units are used to realize electromagnetic energy coupling between every two adjacent resonant cavity units and the two closest non-adjacent resonant cavity units in the N resonant cavity units, and to generate a 180° phase difference between the signal transmitted between the two adjacent resonant cavity units and the signal transmitted between the two closest non-adjacent resonant cavity units.

2. The compact cavity filter with a straight-line configuration introducing a transmission zero according to claim 1, characterized in that, Each resonant rod includes a cuboid metal conductor and a cylindrical metal conductor stacked coaxially. The width of the cuboid metal conductor in the front-to-back direction and the length in the left-to-right direction are both greater than the diameter of the cylindrical metal conductor. The bottom end of the cylindrical metal conductor is fixed to the inner bottom surface of the metal cavity. There is a preset distance between the top end of the cuboid metal conductor and the inner top surface of the metal cavity.

3. The compact cavity filter with a straight-line configuration introducing a transmission zero according to claim 2, characterized in that, Each resonant rod has a cuboid metal conductor with a downwardly recessed first cylindrical hole and a first annular hole at its top. The cuboid metal conductor, the first cylindrical hole, and the first annular hole are coaxially arranged, and the first annular hole is coaxially fitted outside the first cylindrical hole. A first annular body with a preset gap between it and its sidewall is arranged inside the first annular hole. The top of the first annular body is fixed to the inner top surface of the metal cavity. The cuboid metal conductor, the first annular hole, and the first annular body together constitute the first interdigital capacitor structure.

4. The compact cavity filter with a straight-line configuration introducing a transmission zero according to claim 3, characterized in that, Each resonant rod has a cuboid metal conductor with a rearwardly recessed second cylindrical hole and a second annular hole on its front side. The second cylindrical hole and the second annular hole are coaxially arranged, with the second annular hole coaxially fitted outside the second cylindrical hole. A second annular body is arranged inside the second annular hole, maintaining a preset gap with its sidewall. The second annular body is coaxially arranged with the second annular hole. The front end of the second annular body is fixed to the front inner wall of the metal cavity. The cuboid metal conductor, the second annular hole, and the second annular body together constitute the second interdigital capacitor structure.

5. The compact cavity filter with a straight-line configuration introducing a transmission zero according to claim 3, characterized in that, Each frequency fine-tuning unit includes two tuning screws, namely a first tuning screw and a second tuning screw. The first tuning screw penetrates vertically through the inner top surface of the metal cavity and the outer top surface of the metal block via a threaded connection. The second tuning screw penetrates vertically through the front inner wall of the metal cavity and the outer front wall of the metal block via a threaded connection. In a corresponding frequency fine-tuning unit and a resonant cavity unit, the first tuning screw is coaxial with the first cylindrical hole, and its bottom end extends into the first cylindrical hole without contacting the side wall of the first cylindrical hole. The second tuning screw is coaxial with the second cylindrical hole, and its bottom end extends into the second cylindrical hole without contacting the side wall of the second cylindrical hole. By rotating the first tuning screw and the second tuning screw, the relative positions of the first tuning screw and the first cylindrical hole and the second tuning screw and the second cylindrical hole are changed, thereby accurately calibrating the resonant frequency of the resonant cavity unit.

6. The compact cavity filter with a straight-line configuration for introducing transmission zeros according to claim 2, characterized in that, Each coupling control unit includes a coupling screw; N-1 mounting holes 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 arranged linearly in the left-right direction and are located directly below each of two adjacent regions; the N-1 coupling screws are threaded into the N-1 mounting holes, and their top ends extend to the space between two adjacent resonant cavity units; the diameter of the coupling screw included in each coupling control unit is larger than the diameter of the cylindrical metal conductor of all the resonant rods.

7. The compact cavity filter with a straight-line configuration introducing a transmission zero according to claim 6, characterized in that, The coupling screws in the N-1 coupling control units all have the same diameter.

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