A millimeter-wave cavity filter

Abstract

This invention discloses a millimeter-wave cavity filter, relating to the field of filter technology, comprising a metal outer cavity, a metal inner core, and dielectric support strips. The metal outer cavity houses several resonators, each containing a mushroom-shaped parasitic metal pillar. Electrical coupling between the resonators is achieved by a pair of inverted umbrella-shaped pins, while magnetic coupling is achieved through coupling windows. The metal inner core and the metal outer cavity together form a micro-coaxial structure, with periodic window structures on the metal outer wall. This invention significantly reduces the resonant frequency of the resonators without increasing the filter size. It also proposes a micro-coaxial line-coplanar waveguide transition structure and a micro-coaxial line-quasi-planar cavity feeding structure, broadening the application scope of this invention.

Description

Technical Field

[0001] This invention relates to the field of filter technology, and in particular to a millimeter-wave cavity filter. Background Technology

[0002] Filters are an important component of communication systems. Their main function is to extract signals at frequencies of interest and suppress other unwanted signals. Cavity filters have high Q values, large power capacity, and good bandwidth selectivity, making them widely used in various communication systems.

[0003] The size of a cavity filter is related to the resonant frequency of its resonant unit. At lower operating frequencies, cavity filters are generally larger, which is not conducive to system miniaturization and is inconvenient to use. In addition, filters in communication systems need to work in conjunction with other circuits, which means that cavity filters must have circuit-level connectivity. Therefore, it is essential to design a reasonable transition structure from cavity to microstrip and other circuits.

[0004] Cavity filters employ different structures to generate electrical or magnetic coupling. A well-designed coupling path can create transmission zeros, thereby improving the filter's bandwidth selectivity. Under stringent dimensional requirements, the method for designing the coupling structure of the resonator within the cavity is crucial, representing a key step in achieving good electrical performance for the filter. Summary of the Invention

[0005] The problem to be solved by this invention is to design and manufacture a quasi-planar cavity filter using micro-nano fabrication technology. This filter has the advantages of low loss and high selectivity. A novel micro-coaxial line-quasi-planar cavity feeding structure and a micro-coaxial line-coplanar waveguide transition structure are designed to enable the filter to have board-level interconnection and integration capabilities.

[0006] This invention provides the following technical solution: a millimeter-wave cavity filter, comprising:

[0007] The outer metal cavity is composed of several ring-shaped resonators inside, and a mushroom-shaped parasitic metal pillar is loaded at the center of each resonator.

[0008] Several first release holes are formed on the surface of the metal outer cavity for releasing photoresist;

[0009] The two epitaxial cavities are formed by two symmetrical metal cavities extending outward from the resonators, and each cavity contains:

[0010] A metal inner core is disposed within the epitaxial cavity, with one end extending upward and flush with the opening on the epitaxial cavity, serving as a transition structure between the micro coaxial line and the coplanar waveguide. The other end is folded upward and extends into the metal outer cavity, connecting with the upper surface of the metal outer cavity to form the feeding structure of the micro coaxial line-quasi-planar cavity.

[0011] Four medium support bars are used to fix the metal inner core and the outer cavity.

[0012] Preferably, the mushroom-shaped parasitic metal column comprises:

[0013] A hollow cylinder extends upward from the lower wall inside the metal outer cavity;

[0014] A solid cylinder extends downward from the upper wall inside the metal outer cavity. Its radius is smaller than that of the hollow cylinder. The solid cylinder and the hollow cylinder are coaxially arranged, and the solid cylinder extends into the hollow cylinder.

[0015] Preferably, all the resonators form a ring-shaped coupling path, and the coupling method is as follows: the coupling method between the resonators connected end to end on the ring-shaped coupling path is cross coupling, and the coupling between the remaining resonators is main coupling. All the resonators form a complete metal outer cavity through cross coupling and main coupling.

[0016] Preferably, the coupling method between the two resonators includes:

[0017] The magnetic coupling between the two resonators is formed by the coupling window created after part of the sidewalls of the two resonators are removed.

[0018] The electrical coupling between the two resonators is formed by placing two inverted umbrella-shaped pins between the two resonators.

[0019] Preferably, the two umbrella-shaped pins between a pair of electrically coupled resonators are inverted relative to each other, and the two umbrella-shaped pins are a first umbrella-shaped pin and a second umbrella-shaped pin, wherein the wide face of the first umbrella-shaped pin faces upward and the narrow face contacts the lower wall inside the metal outer cavity, and the narrow face of the second umbrella-shaped pin faces upward and the narrow face contacts the upper wall inside the metal outer cavity.

[0020] Preferably, identical epitaxial cavities extend outward from the exterior of two cross-coupled resonators to serve as the input and output ports of the filter. The epitaxial cavity includes a first cavity and a second cavity, and openings are provided on both the first cavity and the second cavity to realize the transition structure.

[0021] Preferably, at the power supply structure, the metal outer cavity is provided with a clamp-shaped second release hole.

[0022] Preferably, the size of the plurality of first release holes is exactly the same.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. The present invention sets a mushroom-shaped parasitic metal pillar in each resonator. The resonant frequency of the resonator is significantly reduced by loading the mushroom-shaped parasitic metal pillar, while ensuring that the volume of the resonator does not increase significantly, which is beneficial to the miniaturization and integration of the system.

[0025] 2. This invention constructs a micro-coaxial line-coplanar waveguide transition structure by extending two epitaxial cavities outside a metal outer cavity connected to a resonator, and by aligning one end of a metal inner core with the opening on the epitaxial cavity. Simultaneously, the other end of the metal inner core is folded upward and extended into the metal outer cavity, connecting with the upper surface of the metal outer cavity, thus forming a micro-coaxial line-quasi-planar cavity feeding structure. This facilitates board-level integration of the cavity filter with other devices and broadens the application range of the cavity filter. Attached Figure Description

[0026] Figure 1 Top and side views of the quasi-planar cavity resonator millimeter-wave filter provided by the present invention;

[0027] Figure 2 This is a schematic diagram of the mushroom-shaped parasitic metal column structure provided by the present invention;

[0028] Figure 3 A schematic diagram of magnetic coupling between resonators provided by the present invention;

[0029] Figure 4 A schematic diagram of the electrical coupling between resonators provided by the present invention;

[0030] Figure 5 A schematic diagram of the micro-coaxial line-coplanar waveguide transition structure and the micro-coaxial line-quasi-planar cavity feeding method provided for this invention;

[0031] Figure 6 The simulation results of the S-parameters of the filter provided by this invention are shown in the figure. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0033] It should be understood in the description of this invention that the terms “center,” “upper,” “lower,” “front,” “rear,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” and “outer,” etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0034] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0035] For the purpose of understanding and explanation, a millimeter-wave cavity filter according to an embodiment of the present invention will be described in detail below.

[0036] like Figure 1-6 As shown, this invention relates to a millimeter-wave cavity filter 10, comprising a metal outer cavity 11, metal inner cores 12 and 13, and dielectric support strips 14, 15, 16, and 17. The filter is manufactured using electrochemical additive manufacturing technology. The outer metal cavity 11 and the metal inner core are both made of copper, and the dielectric support strips have a dielectric constant of 2.85. The outer metal cavity 11 has a vertical thickness of 15 μm and a horizontal thickness of 100 μm.

[0037] The metal outer cavity 11 is divided into four resonators 18, 19, 20, and 21. Several first release holes 22 of identical size are formed on the surface of the metal outer cavity 11 to release photoresist. The size of the first release hole 22 is 200um × 200um × 100um. Mushroom-shaped parasitic metal pillars are loaded at the center of each of the four resonators 18, 19, 20, and 21. The metal outer cavity 11 of resonators 18 and 21 extends outward into a T-shaped epitaxial cavity. The resonators 18 and 21 are electrically coupled by a pair of inverted umbrella-shaped pins 34 and 35. The other resonators 19 and 20 are magnetically coupled through coupling windows 31, 32, and 33. Metal inner cores 12 and 13 are disposed in the T-shaped extended cavity. The metal inner core 13 inside the T-shaped cavity is connected to the T-shaped extended cavity through medium support strips 14, 15, 16 and 17. The metal inner cores 12 and 13 together with the metal outer cavity 11 form a micro coaxial structure. A periodic window structure is provided on the metal outer wall.

[0038] The four resonators 18, 19, 20, and 21 have dimensions similar to their operating frequency. The mushroom-shaped parasitic metal pillars are composed of large-radius hollow cylinders 23, 24, 25, and 26 and small-radius solid cylinders 27, 28, 29, and 30, with the base centers of the two cylinders being the same. The hollow cylinders loaded inside resonators 18 and 21 have an outer diameter of 797.5 μm, an inner diameter of 597.5 μm, and a radius of 297.5 μm for the solid cylinders. The hollow cylinders loaded inside resonators 19 and 20 have an outer diameter of 735 μm, an inner diameter of 535 μm, and a radius of 235 μm for the solid cylinders. The hollow cylinders extend upwards from the lower wall inside the metal cavity 11 to a height of 460 μm, and the solid cylinders extend downwards from the upper wall inside the metal cavity 11 to a height of 460 μm. The two cylinders overlap vertically, meaning a portion of the solid cylinder extends into the hollow cylinder.

[0039] The coupling between resonators 18 and 19 is a narrow-sided windowed magnetic coupling. A portion of the resonator wall is removed to form coupling window 31, with a width of 1520 μm. All diaphragms are 150 μm thick. Similarly, coupling windows 32 and 33 are used to achieve magnetic coupling between resonators 19 and 20, and between 20 and 21. The width of coupling window 32 between resonators 19 and 20 is 1395 μm, and the width of coupling window 33 between resonators 20 and 21 is 1520 μm. The electrical coupling between resonators 18 and 21 is formed by a pair of inverted umbrella-shaped pins 34 and 35. Each pin consists of a wide face (1225 μm × 1225 μm × 100 μm) and a narrow face (200 μm × 200 μm × 460 μm). The first umbrella-shaped pin 34 and the second umbrella-shaped pin 35 are placed in opposite directions in the vertical direction. The narrow side of the first umbrella-shaped pin 34 is connected to the lower wall inside the metal outer cavity 11, and the narrow side of the second umbrella-shaped pin 35 is connected to the upper wall inside the metal outer cavity 11. This structure realizes the electrical coupling between the resonator 18 and the resonator 21.

[0040] There are filter feeding and transfer structures outside resonators 18 and 21. A T-shaped epitaxial cavity extends outward from the metal outer cavity 11 of resonators 18 and 21. The T-shaped epitaxial cavity is composed of a first cavity 36 and a second cavity 37. The second cavity is 200um lower than the first cavity in the vertical direction. The sides of the first cavity and the second cavity have a first release hole 22 with a size of 200um×200um×100um to release photoresist. The upper surface of the second cavity has an opening 38 with a surface size of 380um×677um to realize the transfer structure. The dimensions of the first cavity 36 are 500um × 977um × 860um, and the dimensions of the second cavity 37 are 530um × 1577um × 660um. Inside the T-shaped extended cavity is a metal core 13, which can be divided into four segments. The first segment 39 has dimensions of 200um × 145um × 260um, and its upper surface is flush with the opening of the second cavity 37, serving as a structure for a micro-coaxial line to a coplanar waveguide. The second segment 40 is an impedance transformation structure 40 with a thickness of 160um, a width that gradually changes from 145um to 277um, and a length of 90um. The third segment 41 is a 50-ohm transmission line with a width of 277um, a length of 1070um, and a thickness of 260um. The fourth end 42 is a structure for feeding the micro-coaxial line into the cavity, which extends upward by 200um on the upper surface of the third transmission line, with the same length and width as the 50-ohm transmission line. The feeding and transfer structure at resonator 21 is exactly the same as that at resonator 18, and at the feeding structure, the metal outer cavity 11 has a clamp-shaped second release hole 43.

[0041] The metal core 13 inside the T-shaped epitaxial cavity is connected to the T-shaped epitaxial cavity via dielectric support strips 14, 15, 16, and 17. Three of the dielectric support strips 14, 15, and 16 are perpendicular to the metal core 13, and one dielectric support strip 17 is parallel to the metal core. The dielectric support strips 14, 15, and 16 are H-shaped, with the narrower portions at both ends measuring 160um × 30um × 18um and the wider portion in the middle measuring 737um × 100um × 18um. The wider portion of the dielectric support strip 17, which is parallel to the metal core, has a size of 120um × 100um × 18um, and its narrower portion has the same size as the narrower portions at both ends of the H-shaped support strip.

[0042] The filter in this specific embodiment has a 3dB passband range of 34.3GHz-35.6GHz, a minimum in-band insertion loss of 0.61dB, and a zero at both 33.9GHz and 36.4GHz, which improves the filter's frequency selectivity.

[0043] In summary, the quasi-planar cavity resonator millimeter-wave filter 10 in this embodiment uses the basic design method of cross-coupled filters and is fabricated using micro-nano processes, specifically electrochemical additive manufacturing. This electrochemical additive manufacturing technology yields a low-loss, high-selectivity quasi-planar millimeter-wave filter. The high precision of this process allows for integrated design and mass production of the filter while ensuring its performance. The designed micro-coaxial feeding structure for the quasi-planar cavity is relatively simple and easy to implement. The designed micro-coaxial adapter coplanar waveguide structure enables the filter in this invention to have board-level circuit interconnection capabilities, broadening the application range of this filter.

[0044] The above-described embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited thereto. Any simple changes or equivalent substitutions of the technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention shall fall within the scope of protection of the present invention.

Claims

1. A millimeter-wave cavity filter, characterized in that, include: Metal outer cavity (11); Several resonators (18) are arranged in a ring shape inside the metal outer cavity (11), and a mushroom-shaped parasitic metal pillar is loaded at the center of each resonator (18). One group of adjacent resonators is electrically coupled by a pair of inverted umbrella-shaped pins, and the metal outer cavity (11) of the resonators extends outward with a T-shaped extended cavity; the other resonators are magnetically coupled by coupling windows; the wide face of one umbrella-shaped pin faces upward and the narrow face contacts the lower wall inside the metal outer cavity (11); the narrow face of the other umbrella-shaped pin faces upward and its narrow face contacts the upper wall inside the metal outer cavity (11). Each of the T-shaped extended cavities is provided with a metal core (13). One end of the metal core (13) is a micro coaxial line-coplanar waveguide transition structure, and the other end extends into the metal outer cavity (11) and connects to the upper surface of the metal outer cavity (11) to form a micro coaxial line-quasi-planar cavity feeding structure. The two T-shaped extended cavities are the input port and output port of the filter, respectively. The metal core (13) is divided into four sections. The upper surface of the first section (39) is flush with the opening (38) of the second cavity (37) as a micro coaxial line-coplanar waveguide transition structure. The second section (40) is an impedance transformation structure. The third section (41) is a 50-ohm transmission line section. The fourth section (42) is a micro coaxial line feeding structure to the cavity.

2. A millimeter-wave cavity filter as described in claim 1, characterized in that, The surface of the metal outer cavity (11) is provided with a plurality of first release holes (22), which are used to release photoresist.

3. A millimeter-wave cavity filter as described in claim 1, characterized in that, Each of the mushroom-shaped parasitic metal columns comprises: A hollow cylinder (23) extends upward from the lower wall inside the metal outer cavity (11); A solid cylinder (27) extends downward from the upper wall inside the metal outer cavity (11), and its radius is smaller than that of the hollow cylinder (23). The solid cylinder (27) is located inside the hollow cylinder (23) and the two are coaxially arranged.

4. A millimeter-wave cavity filter as described in claim 2, characterized in that, The T-shaped epitaxial cavity includes a first cavity (36) perpendicular to the metal outer cavity (11) and a second cavity (37) perpendicular to the end of the first cavity (36); the first cavity (36) and the second cavity (37) are both provided with a first release hole (22) to release photoresist, and the upper surface of the second cavity (37) is provided with an opening (38) to realize the transition structure.

5. A millimeter-wave cavity filter as described in claim 1, characterized in that, The metal inner core (13) is connected to the T-shaped extended cavity through four medium support bars (14), three of which are perpendicular to the metal inner core (13) and one is parallel to the metal inner core (13).

6. A millimeter-wave cavity filter as described in claim 1, characterized in that, At the power supply structure, a clamp-shaped second release hole (43) is provided at the metal outer cavity (11) corresponding to the two T-shaped extended cavities.

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