A miniaturized high-Q coaxial resonant cavity and bandpass filter

Abstract

A miniaturized high-Q coaxial resonant cavity, comprising: a metal cavity, a cover plate, and a metal resonant rod; the metal cavity is a three-dimensional geometric shape of a column or a cuboid, and the cover plate is located on the top of the metal cavity, so that the metal cavity becomes a closed space to reduce radiation loss; a metal resonant rod is arranged inside the metal cavity, the upper end of the metal resonant rod is a circular plane, the lower end is a circular plane, and the side surface is a gradually concave structure; the central axis of the metal resonant rod coincides with the central axis of the metal shell; a gap is left between the upper end of the metal resonant rod and the metal cavity to form an open circuit; the lower end of the metal resonant rod is directly connected to the metal cavity to form a short circuit; the size of the filter cavity depends on the specific frequency and Q value requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communication, and in particular relates to a miniaturized coaxial resonant cavity, a bandpass filter and applications. Background Art

[0002] As wireless communication systems develop towards miniaturization and integration, coaxial cavity filters with small size and low loss have become indispensable frequency selection devices in mobile communication base stations, and their design methods have also attracted great attention. The coaxial resonant cavity is the basic resonant unit of the coaxial cavity filter, and its volume and Q value reflect the overall size and loss performance of the designed filter. The larger the volume of the resonant cavity, the higher the Q value and the lower the loss. Therefore, the traditional miniaturization design of coaxial filters requires a certain trade-off balance between volume and Q value based on performance indicators. For example, the capacitor cap loading technology loads a metal cap with a larger diameter on the upper end of the coaxial resonant rod to increase the equivalent capacitance of the cavity, thereby reducing the resonant frequency. However, this method also reduces the cavity Q value at a similar ratio.

[0003] CN 116190950A discloses a miniaturized dual coaxial cavity filter designed as "a miniaturized dual coaxial cavity filter, control method and application", which adopts a resonant cavity with a coaxial nested structure, "including a metal cavity, a cover plate, a supporting medium, a slotted resonant column, a feeder, and two SMA-K type connectors; the metal cavity is composed of three small single resonant cavities in cascade, and the single resonant cavity is composed of a cavity and two slotted resonant columns of different sizes, the two slotted resonant columns are nested and reused up and down, the wall thickness of the slotted resonant columns in the resonant cavities at both ends is 0.6mm, and the wall thickness of the slotted resonant columns inside and outside the middle resonant cavity is 1.7mm, forming a third-order miniaturized coaxial filter symmetrical with the middle cavity. The present invention is provided with a single-column slot-shaped structure that is convenient for multiplexing of multiple resonant columns, and multiple resonant columns are multiplexed by loading a single cavity." The utilization rate of the cavity volume is improved and the overall size of the designed filter is reduced. This structure still reduces the Q value, and the dual coaxial nesting inside the single cavity increases the complexity of processing and production.

[0004] CN 214477826U discloses a miniaturized dielectric-loaded coaxial filter designed as "a miniaturized low-frequency cavity filter", which increases the resonant capacitance by loading a dielectric block, keeps the cavity volume unchanged while reducing the cavity resonant frequency. The introduction of a dielectric block can maintain the high Q value of the cavity, but the dielectric material is limited and the processing cost increases. In addition, the tuning nut needs to pass through the dielectric block and insert the resonant rod, and the connection structure is complicated, which increases the tuning complexity of the filter. CN201910674490.6 discloses a coaxial cavity duplexer, including a metal cavity and an input and output port; the metal cavity is in a "convex" shape, and is distinguished by four resonant cavities.

[0005] Through the above analysis, the existing technology does not fundamentally solve the problem of miniaturizing the coaxial resonant cavity while maintaining a high Q value or low loss without increasing the processing and debugging costs. Summary of the invention

[0006] The purpose of the present invention is to break through the bottleneck of the prior art and to provide a miniaturized high-Q coaxial resonant cavity, a bandpass filter and applications.

[0007] The present invention adopts the following technical scheme: a miniaturized high-Q coaxial resonant cavity, comprising: a metal cavity, a cover plate, and a metal resonant rod; the metal cavity is a three-dimensional (column, cuboid, etc.) geometric shape of the filter cavity, and the cover plate is located at the top of the metal cavity, so that the metal cavity becomes a closed space to reduce radiation loss; a metal resonant rod is arranged inside the metal cavity, the upper end of the metal resonant rod is a circular plane, the lower end is a circular plane, and the side surface is a gradually concave structure; the central axis of the metal resonant rod coincides with the central axis of the metal shell; a gap is left between the upper end of the metal resonant rod and the metal cavity to form an open circuit; the lower end of the metal resonant rod is directly connected to the metal cavity to form a short circuit. The size of the filter cavity depends on the specific frequency and Q value requirements. Usually, the metal shell, the metal column in the cavity, and the gap comprehensively determine the frequency and Q value of the resonant cavity. When the size of the external metal shell is constant, the length of the internal metal rod is approximately equal to 1 / 4 wavelength. (Wavelength = speed of light / frequency, in meters) Therefore, the longer the internal metal resonant rod is, the lower the frequency will be, but at the same time, the Q value will also decrease. Especially when approaching the top, the frequency and Q value will decrease rapidly.

[0008] The gap is 3±1mm to facilitate the tuning process after processing. However, when the frequency has an edge of microwave frequency, the gap range is larger.

[0009] The size of the metal cavity (shell) of the coaxial resonant cavity of the present invention and the length of the gap all follow the existing design. The difference is that the depression can achieve unexpected effects; regarding the size, if it is for the following embodiments or for a specific frequency, we can give each specific size, which can be seen in the following embodiments. If it covers the entire microwave band, the size range is very large.

[0010] The gradually changing inner concave side surface of the metal resonance rod is obtained by rotating a concave curve function around a main axis.

[0011] The concave curve function is represented by fx, which is any function that satisfies the following formula, where x1 and x2 are any two values ​​in the domain:

[0012]

[0013] The concave curve function includes parabolic function, hyperbolic function, hemispherical function, elliptical curve, oval, involute, catenary; or a concave curve synthesized by several concave curve functions; any concave function, whether alone or synthesized by several, meets the definition of the formula. Or the concave curve can be an arc that cannot be expressed analytically, and can be a concave arc drawn or programmed.

[0014] If it is for a certain embodiment, the domain of x can be [-L / 2, L / 2], where L is the length of the internal resonance rod and the coordinate origin is in the middle of the metal resonance rod (the largest depression).

[0015] The concavity of the side surface determines the resonant frequency and Q value of the coaxial resonant cavity.

[0016] The greater the depression of the side surface, the lower the resonance frequency.

[0017] As the concavity of the side surface increases, the Q value increases first and then decreases. The Q value satisfies:

[0018]

[0019] Among them, C is a constant, a is the side length of the metal cavity, Ra is the geometric mean radius of the metal resonant rod, and L is the height of the metal resonant rod. The definition of the geometric mean radius refers to the definition of the geometric mean in calculus, and finally the expression of the geometric mean radius can be obtained as:

[0020]

[0021] Further, a coaxial cavity bandpass filter is provided, including a filter cavity cover, a filter cavity, an SMA connector (joint), and four resonant rods (same as the above-mentioned coaxial resonant cavity structure) are arranged in the filter cavity, namely, a first resonant rod, a second resonant rod, a third resonant rod, and a fourth resonant rod; the filter cavity is a three-dimensional (rectangular) geometric figure, and the filter cavity cover is located at the top of the filter cavity to form a closed cavity; the first resonant rod, the second resonant rod, the third resonant rod, and the fourth resonant rod are all connected to the filter cavity to form a short circuit, and a gap is left with the filter cover to form an open circuit; the coaxial cavity bandpass filter uses two SMA connectors for energy input and output. The coaxial cavity bandpass filter is formed by linearly cascading four miniaturized high-Q coaxial resonant cavities.

[0022] Furthermore, the coaxial cavity bandpass filter is an axisymmetric structure, so the sizes of the four miniaturized high-Q coaxial resonant cavities are the same in pairs, forming two filtering frequencies.

[0023] Furthermore, the SMA connector is placed on both sides of the input and output of the coaxial cavity bandpass filter, and the coaxial cavity bandpass filter is connected to an external circuit and matched with the external circuit through the SMA connector and a 50Ω characteristic impedance transmission line.

[0024] The present invention is applied to communication equipment, and uses the miniaturized high-Q value coaxial resonant cavity or coaxial cavity bandpass filter of the present invention.

[0025] Beneficial effects of the present invention: The coaxial resonant cavity with a metal resonant rod with a concave side surface provided by the present invention can achieve a 10% improvement in Q value under the condition of a 20% reduction in volume, compared with an existing coaxial resonant cavity with a standard metal resonant rod of the same volume, through the concave side surface. The bandpass filter provided by the present invention can be formed by cascading the coaxial resonant cavity through the filter comprehensive theory, and can achieve a reduction in volume and an improvement in performance compared with a bandpass filter with the same cascade topology.

[0026] The creative effect of the present invention is also reflected in that it solves the problem that the miniaturization of the coaxial resonant cavity and the high Q value cannot be achieved at the same time, breaking through the bottleneck of the prior art. Compared with miniaturized cavity technologies such as capacitor loading and dielectric loading, it has a simple structure, low loss and is easy to implement. The design of the bandpass filter based on the coaxial resonant cavity will not increase the design, processing, tuning complexity and production cost, and there is no need to introduce a special bandpass filter design method. It can be widely used in the miniaturization and high-performance design of coaxial cavity filters in different bands such as 4G and 5G. The bandpass filter can be obtained by cascading the miniaturized high-Q value coaxial resonant cavity through the comprehensive theory of classical filters.

[0027] The present invention solves the problems of miniaturization and high Q value of the metal coaxial resonant cavity without increasing the processing and design costs, and has universal applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the miniaturized high-Q coaxial resonant cavity structure provided by the present invention.

[0029] Figure 2 It is a schematic diagram of a numerical simulation curve of the influence of the recess degree k on the resonance frequency f and the Q value provided in Example 1 of the present invention.

[0030] Figure 3 Schematic diagram of the structure of a fourth-order bandpass filter in Example 2 of the present invention.

[0031] Figure 4 This is an S parameter diagram of the fourth-order bandpass filter in Example 2 of the present invention.

[0032] Figure 5 This is a schematic diagram of the structure of a miniaturized high-Q value cylindrical coaxial resonant cavity provided in Example 3 of the present invention.

[0033] Figure 6 It is a schematic diagram of a numerical simulation curve of the influence of the recess degree k2 on the resonance frequency f and the Q value provided in Example 3 of the present invention.

[0034] Figure 7 It is a front view of the fourth-order bandpass filter in embodiment 4 of the present invention.

[0035] Figure 8 This is a top view of the fourth-order bandpass filter in Example 4 of the present invention.

[0036] Fig. 9 4 is an S parameter diagram of the fourth-order bandpass filter in Example 4 of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention is described in detail below in combination with the embodiments of the present invention and its accompanying drawings. Obviously, the coaxial resonant cavity and bandpass filter embodiments described are part of the embodiments of the present invention and do not include all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] A maximum (optimal) depression value of the present invention can be expressed by the formula: k = (-12.5309 + 6*R) / L 2 . Where R is the radius of the upper and lower cylindrical surfaces of the internal resonant rod, and L is the length of the internal resonant rod (in mm). For example, R = 4, L = 13.15, then the concave value k = 0.066. Therefore, the concave value is much smaller than the radius. However, it should be noted that there is a certain error in this formula.

[0039] In fact, this is the best depression value, which can guarantee the maximum Q value. If it is the maximum depression value, as long as it can be processed. In other words, the most depressed part in the middle of the resonance rod is greater than 2mm or even 1mm, which can ensure processing and a certain strength support. Generally speaking, the maximum depression value can be more than 5% of the cylindrical radius of the resonance rod; if expressed as a function, the concave curve function form determines the gradual depression form of the side surface of the metal resonance rod, and the depression degree of the concave curve function determines the gradual depression degree of the side surface of the metal resonance rod. Concave curves expressed by non-functions are also acceptable (generally refers to relatively uniform and continuous arc depressions).

[0040] Example 1

[0041] like Figure 1As shown, the embodiment of the present invention provides a miniaturized high-Q coaxial resonant cavity, including: a metal cavity 1, a cover plate 2, and a metal third resonant rod; the metal cavity is a three-dimensional geometric shape, and the cover plate 2 is located on the top of the metal cavity 1, so that the resonant cavity becomes a closed space to reduce radiation loss; the height of the metal third resonant rod is L mm; the upper and lower ends of the metal third resonant rod are a circular plane with a radius of R mm; the side surface of the metal third resonant rod is a gradual concave structure; the central axis of the metal third resonant rod coincides with the central axis of the metal shell; a gap is left between the upper end of the metal third resonant rod and the cover plate 2, and the gap height is h-Lmm, forming an open circuit; the lower end of the metal third resonant rod is connected to the metal cavity 1 to form a short circuit. The gap range generally has no fixed value, the low frequency is greater than 3mm, and there are also those below 3mm. A specific value can be given in a specific embodiment. As described in the example.

[0042] like Figure 1 As shown, the concave side surface of the third metal resonance rod is obtained by rotating the parabolic function fx around the main axis x; the parabolic function is expressed by fx as:

[0043] f(x)=k·L 2 +R,x∈[-L / 2,L / 2]

[0044] Where k is the concavity coefficient. The larger k is, the greater the concavity is.

[0045] The depression coefficient k can control the resonance frequency f and Q value of the coaxial resonant cavity.

[0046] Figure 2 The resonant frequency f and Q value are shown as a function of k. The metal is aluminum, and the conductivity σ is 3.6×10 7 S / m. The greater the depression degree k, the longer the electrical length of the coaxial resonant cavity and the lower the resonant frequency f; the greater the depression degree k, the higher the Q value of the coaxial resonant cavity first and then decreases.

[0047] The Q value of the coaxial resonant cavity satisfies:

[0048]

[0049] C is a constant, a is the side length of the metal cavity, Ra is the geometric mean radius of the metal resonant rod, and L is the height of the metal resonant rod. The definition of the geometric mean radius refers to the definition of the geometric mean in calculus, and the final expression of the geometric mean radius is:

[0050]

[0051] Specifically, when k = 0.05, the coaxial resonant cavity frequency is 3.31 GHz and the Q value is 3386; in contrast, when k = 0, the resonant frequency is 4.21 GHz and the Q value is 3041. With the metal cavity volume unchanged, a 21.37% volume reduction and a 10.12% Q value increase were achieved, breaking through the bottleneck of existing technologies.

[0052] Example 2

[0053] like Figure 3 As shown, on the basis of the above embodiment, the embodiment of the present invention provides a coaxial bandpass filter based on the above miniaturized high-Q coaxial resonant cavity, comprising: a filter cavity cover plate 4, a filter cavity 5, an SMA connector 6, a first resonant rod 7, a second resonant rod 8, a third resonant rod 9, and a fourth resonant rod 10. The filter cavity cover plate 4 is located at the top of the filter cavity 5 to form a closed space; the first resonant rod 7, the second resonant rod 8, the third resonant rod 9 and the fourth resonant rod 10 are all concave and connected to the filter cavity 5 to form a short circuit, and a gap is left with the filter cover plate 4 to form an open circuit; the fourth-order coaxial bandpass filter uses two SMA connectors 6 for energy input and output.

[0054] The SMA connector is placed on both sides of the input and output of the coaxial cavity bandpass filter, and the coaxial cavity bandpass filter is connected to the external circuit and matched with the external circuit through the SMA connector and the 50Ω characteristic impedance transmission line. Like the SMA connector, the present invention can be applied to the microwave field with a frequency range up to 26.5GHz.

[0055] The coaxial cavity bandpass filter is formed by linearly cascading four miniaturized high-Q value coaxial resonant cavities.

[0056] The coaxial cavity bandpass filter is an axisymmetric structure, so the sizes of the four miniaturized high-Q coaxial resonant cavities are the same in pairs.

[0057] The first resonant rod 7 and the fourth resonant rod 10 have the same size, a concave degree of 0.0541, a height of L1 = 13.59 mm, and a radius of R1 = 4 mm.

[0058] The second resonant rod 8 and the third resonant rod 9 have the same size, a concave degree of 0.0453, a height of L2=13.5 mm, and a radius of R2=4 mm.

[0059] 1. As Figure 4 As shown, the filter resonant frequency is 3.5GHz, and the return loss S is within 3.4-3.6GHz. 11 Greater than 20dB, insertion loss S 21 Less than 0.2dB.

[0060] 2. The present invention solves the problem that miniaturization and high Q value of coaxial cavity bandpass filter cannot be obtained at the same time, and realizes that the Q value reaches more than 3000 in a volume of one-seventh wavelength.

[0061] 4. The present invention does not increase any complexity of design, processing, tuning, etc. of the coaxial bandpass filter, does not require the introduction of special design methods, has universal practicality and applicability, and can quickly replace the coaxial cavity filter in the existing communication system.

[0062] Example 3

[0063] like Figure 5 As shown, an embodiment of the present invention provides a miniaturized high-Q value cylindrical coaxial resonant cavity, comprising: a cylindrical cavity 11, a circular cover plate 12, and a fifth resonant rod 13; the cylindrical cavity 11 is a three-dimensional geometric shape, and the circular cover plate 12 is located on the top of the cylindrical cavity 11, so that the resonant cavity becomes a closed space to reduce radiation loss; the height of the fifth resonant rod is L3 mm; the upper and lower ends of the fifth resonant rod are a circular plane with a radius of R3 mm; the side surface of the fifth resonant rod is a gradually concave structure; the central axis of the fifth resonant rod coincides with the central axis of the metal shell; a gap is left between the upper end of the fifth resonant rod and the circular cover plate 12, and the gap height is h2-L3 mm, forming an open circuit; the lower end of the fifth resonant rod is connected to the cylindrical cavity 11 to form a short circuit. As shown Figure 5 As shown, the inner concave side surface of the fifth resonant rod is obtained by rotating the parabolic function fx around the main axis x; the parabolic function is expressed by fx as:

[0064] f(x)=k2·L 2 +R,x∈[-L3 / 2,L3 / 2]

[0065] Where k2 is the concavity coefficient. The larger k2 is, the greater the concavity is.

[0066] The recess coefficient k2 can control the resonant frequency f and Q value of the coaxial resonant cavity.

[0067] Figure 6 The resonant frequency f and Q value are shown as a function of k2. The metal is aluminum, and the conductivity σ is 3.6×10 7 S / m. The greater the depression degree k2, the longer the electrical length of the coaxial resonant cavity and the lower the resonant frequency f; the greater the depression degree k2, the higher the Q value of the coaxial resonant cavity first and then decreases.

[0068] The Q value of the coaxial resonant cavity satisfies:

[0069]

[0070] Where C is a constant, R cis the cavity radius of the cylindrical coaxial resonant cavity, and Ra is the average radius of the fifth resonant rod.

[0071] Specifically, when k2 = 0.06, the coaxial resonant cavity frequency is 5.06 GHz and the Q value is 3476.8; in contrast, when k2 = 0, the resonant frequency is 5.67 GHz and the Q value is 3276.5. While the volume of the metal cavity remains unchanged, a 21.37% volume reduction and a 10.12% Q value increase are achieved, breaking through the bottleneck of existing technologies.

[0072] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

[0073] Example 4

[0074] like Figure 7 , Figure 8 As shown, on the basis of the above-mentioned embodiment 3, the embodiment of the present invention provides a coaxial bandpass filter based on the above-mentioned miniaturized high-Q value cylindrical coaxial resonant cavity, including: a cylindrical filter cover 14, a cylindrical filter cavity 15, an SMA connector 16, a sixth resonant rod 17, a seventh resonant rod 18, an eighth resonant rod 19, and a ninth resonant rod 20. The cylindrical filter cavity cover 14 is located at the top of the cylindrical filter cavity 15 to form a closed space; the sixth resonant rod 17, the seventh resonant rod 18, the eighth resonant rod 19 and the ninth resonant rod 20 are all concave and connected to the cylindrical filter cavity 15 to form a short circuit, and a gap is left with the cylindrical filter cover 14 to form an open circuit; the fourth-order coaxial bandpass filter uses two SMA connectors 16 for energy input and output. The SMA connectors are placed on the input and output sides of the coaxial cavity bandpass filter, and the coaxial cavity bandpass filter is connected to the external circuit and matched with the external circuit through the SMA connector and the 50Ω characteristic impedance transmission line. Like the SMA connector, the present invention can be applied to the microwave field with a frequency range up to 26.5 GHz.

[0075] The coaxial cavity bandpass filter is formed by linearly cascading four miniaturized high-Q value cylindrical coaxial resonant cavities.

[0076] The coaxial cavity bandpass filter is an axisymmetric structure, so the sizes of the four miniaturized high-Q value cylindrical coaxial resonant cavities are the same in pairs.

[0077] The sixth resonant rod 17 and the ninth resonant rod 20 have the same size, a concave degree of 0.0825, a height of L4=10.00 mm, and a radius of R4=3 mm.

[0078] The seventh resonant rod 18 and the eighth resonant rod 19 have the same size, a concave degree of 0.0747, a height of L5=9.65 mm, and a radius of R2=3 mm.

[0079] like Fig. 9 As shown, the filter resonant frequency is 5 GHz, and the return loss S is within 4.89–5.19 GHz. 11 Less than -20dB, insertion loss S 21 Greater than -0.2dB.

[0080] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A miniaturized high-Q coaxial resonant cavity, characterized in that: include: Metal cavity, cover plate, metal resonant rod; The metal cavity is a filter cavity, which is a three-dimensional geometric shape of a cylinder or a cuboid. The cover plate is located on the top of the metal cavity, so that the metal cavity becomes a closed space to reduce radiation loss. A metal resonance rod is arranged inside the metal cavity, the upper end of the metal resonance rod is a circular plane, the lower end is a circular plane, and the side surface is a gradually concave structure. The central axis of the metal resonance rod coincides with the central axis of the metal shell. A gap is left between the upper end of the metal resonance rod and the metal cavity to form an open circuit. The lower end of the metal resonance rod is directly connected to the metal cavity to form a short circuit. The size of the filter cavity depends on the specific frequency and Q value requirements. The gradually changing inner concave side surface of the metal resonance rod is obtained by rotating a concave curve function around a main axis; The concave curve function is represented by fx, which is any function that satisfies the following formula, where x1 and x2 are any two values ​​in the domain: The concave curve function includes a parabolic function, a hyperbolic function, a hemispherical function, an elliptical curve, an oval, an involute, and a catenary; or the concave curve is a concave curve synthesized by several concave curve functions; or the concave curve is an arc represented non-analytically; The degree of depression of the side surface determines the resonant frequency and Q value of the coaxial resonant cavity; the greater the degree of depression of the side surface, the lower the resonant frequency; The greater the concavity of the side surface, the greater the Q value first increases and then decreases; the Q value satisfies: , where C is a constant, a is the side length of the metal cavity, Ra is the geometric mean radius of the metal resonant rod, and L is the height of the metal resonant rod.

2. The high-Q coaxial resonant cavity according to claim 1, characterized in that: The gap is 3±1mm.

3. A coaxial cavity bandpass filter prepared according to any one of claims 1 to 2 with a high Q value coaxial resonant cavity, characterized in that: The coaxial cavity bandpass filter is formed by linearly cascading four high-Q coaxial resonant cavities; it includes: a filter cavity cover, a filter cavity, an SMA connector, a first resonant rod, a second resonant rod, a third resonant rod, and a fourth resonant rod; the filter cavity is a three-dimensional geometric figure, and the filter cavity cover is located on the top of the filter cavity to form a closed cavity; the first resonant rod, the second resonant rod, the third resonant rod, and the fourth resonant rod are all connected to the filter cavity to form a short circuit, and a gap is left with the filter cover to form an open circuit; the coaxial cavity bandpass filter uses two SMA connectors for energy input and output.

4. The coaxial cavity bandpass filter according to claim 3, characterized in that: The coaxial cavity bandpass filter is an axisymmetric structure, so the sizes of the four miniaturized high-Q coaxial resonant cavities are the same in pairs.

5. The coaxial cavity bandpass filter according to claim 4, characterized in that: SMA connectors are arranged on both sides of the input and output of the coaxial cavity bandpass filter, and the coaxial cavity bandpass filter is connected to an external circuit and matched with the external circuit through the SMA connector and a 50Ω characteristic impedance transmission line.

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