Microwave resonator for compact rubidium atomic clocks and method of use thereof

Abstract

The application provides a microwave resonant cavity for a compact rubidium atomic clock and a use method thereof, and belongs to the technical field of atomic clock microwave. The application realizes the miniaturization of the cavity under the premise of ensuring the accommodation of a 25mm rubidium atomic gas chamber, has a higher field factor, a Q factor and a higher magnetic coupling efficiency, helps to improve the frequency stability and the signal-to-noise ratio of the rubidium atomic clock, and can solve the problems of large cavity volume and poor magnetic field uniformity of the traditional TE011 mode cylindrical resonant cavity.

Description

Technical Field

[0001] This invention belongs to the field of atomic clock microwave technology, and relates to a compact microwave resonant cavity for rubidium atomic clocks and its usage method, particularly to a high field factor compact microwave resonant cavity for rubidium atomic clocks and its usage method. Background Technology

[0002] Rubidium atomic clocks, as high-precision secondary frequency standards, play an irreplaceable role in satellite navigation, deep space signals, and 5G / 6G synchronization networks. Their core advantage lies in their excellent short-term stability. To ensure efficient excitation of rubidium atoms, traditional microwave resonant cavities are typically designed as cylindrical chambers using TE (Transient Voltage) clocks. 011 This mode, which can significantly increase the Q value by increasing the cavity volume and has a central magnetic field parallel to the optical axis, is beneficial for exciting rubidium atoms to undergo Zeeman transitions. However, this resonant cavity suffers from problems such as difficulty in distinguishing modes and a decrease in the field orientation factor after the volume increases, excessive undercoupling of the magnetic coupling ring leading to low excitation efficiency, uneven excitation efficiency, reduced signal-to-noise ratio (S / N) of the clock signal, and deterioration of frequency stability.

[0003] In 2009, the Lanzhou Institute of Space Technology Physics proposed a TE... 111 The cylindrical microwave resonant cavity in this mode achieves miniaturization of the cavity design, but TE 111 Compared to TE mode 011 The mode suffers from low Q-value and field orientation factor. In 2014, Xiamen University proposed a TE mode with a filled medium. 101 The TE mode resonator achieved a smaller design and a higher Q factor, but still suffered from poor magnetic field distribution and a low field factor, and the magnetic field strength was relatively low at the location where the rubidium bulb was placed. In 2018, the Lanzhou Institute of Space Technology Physics proposed the TE mode resonator. 011 The annular gap resonator of the mode uses a slow wire EDM process and four electrodes, achieving both a high field orientation factor and Q value. However, the radius of the annular gap cavity is only 5.2 mm, which presents a problem of not being able to effectively accommodate the rubidium atom gas cell.

[0004] In summary, the use of magnetron resonant cavities provides a solution for optimizing the volume and performance of resonant cavities. It can effectively improve the field orientation factor (high magnetic field uniformity) and the Q factor (cavity quality factor) of the resonant cavity, and realize the miniaturization of the resonant cavity while accommodating a larger rubidium bulb. Summary of the Invention

[0005] To address the aforementioned technical bottlenecks and issues encountered in engineering, such as processing error compensation and gas chamber sintering structure containment, this invention provides a compact microwave resonant cavity design that offers high magnetic field uniformity, solving the problems of traditional TE 011 The problem of balancing miniaturization and high performance in cylindrical resonators.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A compact microwave resonant cavity for rubidium atomic clocks is disclosed, featuring an innovative two-segment cavity and annular gap circumferential asymmetric electrode structure. This design achieves miniaturization while maintaining high Q-factor, field orientation factor, and coupling efficiency, and can accommodate a 25mm rubidium atomic gas cell with a sintered sidewall structure. The microwave resonant cavity is a hollow cylindrical structure, comprising a coaxial cable 1, an upper end cover 2, an upper end cover threaded ring 3, a main cavity wall 4, a lower end cover threaded ring 5, a lower end cover 6, electrodes 7 located inside the main cavity wall 4, a rubidium atomic gas cell support 8, and a rubidium atomic gas cell 9. The resonant cavity is a hollow cylindrical structure formed by the combination of an upper end cover 2, a lower end cover 6, and a main cavity wall 4. This structure is defined as both a cavity sealing structure and a tuning structure. It contains two interconnected cylindrical cavities with different inner diameters. The cavity formed by the combination of the upper end cover 2 and the main cavity wall 4 has a larger inner diameter and is defined as the main cavity. The cylindrical cavity located inside the lower end cover 6 has a smaller inner diameter and is defined as the secondary cavity 604. The upper end cover 2 and the lower end cover 6 are installed at both ends of the main cavity wall 4. The inner wall of the main cavity has six electrode segments 7, forming annular gap electrodes. The threaded mounting holes on the upper end cover 2 are used to install the coaxial cable 1. The threaded rings 3 and 5 of the upper and lower end covers are located at both ends of the main cavity wall 4 and are locked together by threaded structures, completing the cavity sealing and tuning assembly positioning. Specifically: The upper cover 2 includes an integrally formed circular cover plate and a cylindrical protrusion located inside the circular cover plate. The circular cover plate is a flat cylindrical structure, and the cylindrical protrusion extends axially from the inside of the circular cover plate. Its outer diameter is smaller than that of the circular cover plate and equal to the inner diameter of the tubular main cavity wall 4. The two are integrally formed. A through-hole 202 is provided at the center of the cylindrical structure for laser irradiation of the rubidium atom gas chamber. Next to the through-hole, a sixth threaded hole 205 and a positioning hole 206 are provided for fixing the coaxial cable 1. On the side wall of the cylindrical protrusion, thirty rectangular cross-section protrusions extending axially are distributed circumferentially, defined as upper cover protrusions 204, which correspond one-to-one with the main cavity wall grooves 402 provided axially on the side wall of the main cavity wall 4. On the end face of the cylindrical protrusion, thirty radial upper cover grooves 201 with rectangular cross-sections are provided. The upper end cover groove 201 is circumferentially distributed and its position is aligned with the upper end cover protrusion 204. The edge of the circular cover plate has six axially penetrating first threaded through holes 203. When the upper end cover 2 is assembled with the main cavity wall 4, the cylindrical protrusion of the upper end cover 2 is inserted into one end of the main cavity wall 4. The upper end cover protrusion 204 and the insertable groove 402 in the main cavity wall allow the cylindrical protrusion to be precisely embedded in the main cavity wall 4, achieving radial positioning and circumferential sealing. Simultaneously, the upper end cover groove 201 communicates with the main cavity wall groove, together forming an axially penetrating groove. The upper end cover threaded ring 3 is located inside the circular cover plate of the upper end cover 2.

[0007] Furthermore, the rectangular cross-section protrusions are non-uniformly distributed circumferentially, totaling 30, specifically: five protrusions per group, divided into six groups; within the same group, the central angle between adjacent protrusions is 10 degrees; between two adjacent groups, i.e., between the last protrusion of the previous group and the first protrusion of the next group, the central angle is 20 degrees; the central angle is the circumferential angle formed on the radial cross-section of the cavity with the central axis of the cavity as the vertex. Multiple groups of upper end cap protrusions 204 and upper end cap grooves 201 are uniformly arranged circumferentially with a period of 60 degrees. The lower end cap 6 has a similar main structure to the upper end cap 2, but has a unique design that forms a separate secondary cavity 604. It also includes an integrally formed circular cover plate and a lower end cap cylindrical protrusion 607 located inside the circular cover plate. The cylindrical protrusion has thirty axially extending rectangular protrusions on its side, used to cooperate with the main cavity wall groove 402 axially arranged at the bottom of the main cavity wall 4. On the end face of the lower end cover 6 corresponding to the cylindrical protrusion, there are 30 radial, rectangular cross-section lower end cover grooves 603, which serve the same function as the upper end cover grooves 201. The key difference between the lower end cover 6 and the upper end cover 2 is that the central portion of the inner end face of the cylindrical protrusion of the lower end cover 6 is axially cut off to form a cylindrical blind hole structure, namely the secondary cavity 604. The circular cover plate of the lower end cover 6 has six third threaded through holes 601 along the axial direction. The central portion of the outer end face of the circular cover plate is axially cut off to form a blind hole structure, defined as a cylindrical lens groove 605, for installing an optical lens. A through hole is drilled between the lens groove 605 and the secondary cavity 604 to form a light-transmitting hole 602 for the lower end cover. The threaded ring 5 of the lower end cover is located on the inner side of the circular cover plate of the lower end cover 6.

[0008] Furthermore, the inner diameter of the secondary cavity 604 is between the inner diameter of the main cavity wall 4 and the inner diameter of the lower end cover light-transmitting hole 602, and is used to accommodate the bulb body of the rubidium atom gas chamber 9. The lower end cover light-transmitting hole 602 has the same function as the upper end cover light-transmitting hole 202. The laser light passes through the lens groove 605, is refracted by the lens, and then passes through the lower end cover light-transmitting hole 602 before irradiating the rubidium atom gas chamber and exiting through the upper end cover light-transmitting hole 202.

[0009] The main cavity wall 4 is a tubular structure open at both ends along the axial direction. Its inner wall has thirty parallel grooves 402 that penetrate both ends axially. Five grooves form a group, creating six groups of grooves. Electrodes 7 are installed between adjacent groups of grooves on the inner wall of the main cavity wall 4, with the distribution pattern similar to the upper end cap protrusion 204. Between adjacent groups of grooves, there are two second threaded through holes 401 that penetrate the main cavity wall 4 radially, forming a threaded locking structure with the fifth threaded hole 705 to fix the electrodes 7 to the inner wall of the main cavity wall 4. Thus, the multiple groups of main cavity wall grooves 402 and second threaded through holes 401 are evenly arranged circumferentially at a period of 60 degrees. Second thread lines 403 are provided on the outer wall surfaces at both the upper and lower ends of the main cavity wall 4.

[0010] Furthermore, the cross-section of the main cavity wall groove 402 is rectangular.

[0011] The upper end cap 2 and lower end cap 6 are connected to the main cavity wall 4 through a dual method of precision fitting and locking with threaded rings on the upper and lower end caps, ensuring the cavity's sealing and mechanical tuning functions. The upper end cap 2 and lower end cap 6 are inserted into the inner cavity of the main cavity wall 4 from both ends via rectangular protrusions on their cylindrical protrusions. The protrusions form a clearance fit with the main cavity wall groove 402, ensuring precise alignment of the upper end cap groove 201 and the lower end cap groove 603 with the main cavity wall groove 402, forming a complete through-groove structure. This design guarantees the electromagnetic sealing of the cavity interior (except for the light-transmitting holes). Furthermore, the upper end cap threaded ring 3 and lower end cap threaded ring 5 are both circular rotating components with a rectangular cross-section. The lower end cap threaded ring 5 is thicker than the upper end cap threaded ring 3, while the other characteristics of both are identical. The inner ring sidewall of the upper end cap threaded ring 3 is provided with a first thread 303, which is used to engage with the second thread 403 on the upper outer wall of the main cavity wall 4, thereby adjusting and locking the axial position of the upper end cap 2. On the end face of the upper end cap threaded ring 3, 24 first threaded holes 301 are evenly distributed circumferentially along the edge of the ring and are completely penetrating axially. After the first threaded holes 301 are aligned with the fixing through holes on the edge of the upper end cap 2, screws are screwed in to lock the upper end cap threaded ring 3 to the upper end cap 2. Between any two adjacent first threaded holes 301, there are two second threaded holes 302 with the same diameter penetrating the inner and outer walls of the threaded ring. When the upper end cap threaded ring 3 is screwed in along the second thread 403 on the upper outer wall of the main cavity wall 4 and adjusted to the target axial position, a set screw is screwed into the second threaded hole 302, so that the end of the screw presses against the outer wall of the main cavity wall 4, thereby fixing the upper end cap threaded ring 3 to the main cavity wall 4 and preventing the threaded ring from rotating spontaneously and changing its axial position. Correspondingly, the inner ring sidewall of the lower end cover threaded ring 5 is provided with a third thread 503, and 24 axially penetrating third threaded holes 501 are evenly distributed on the end face. Among them, there are two fourth threaded holes 502 that penetrate the inner and outer sidewalls of the threaded ring along the same diameter between adjacent third threaded holes 501. Its structure and connection relationship are completely consistent with the upper end cover threaded ring 3, except that the axial thickness is larger to adapt to the larger tuning distance assembly requirements of the lower end cover 6.

[0012] Six electrodes 7 are distributed circumferentially at 60-degree intervals in the groove-free area of ​​the main cavity wall 4, forming an annular electrode structure. The six electrodes 7 are of two types: two symmetrical electrodes and four asymmetrical electrodes. The two symmetrical electrodes are arranged adjacently, and the four asymmetrical electrodes are arranged adjacently, specifically: a first symmetrical electrode, a second symmetrical electrode, a first asymmetrical electrode, a second asymmetrical electrode, a third asymmetrical electrode, and a fourth asymmetrical electrode. Both types of electrodes are columnar structures formed by axial stretching of a T-shaped cross-section. Each electrode 7 has an electrode support column 703 integrally connected to its outer side. The T-shaped structure of the symmetrical electrode is planar symmetrical, with equal lengths at both ends of the T. The T-shaped structure of the asymmetrical electrode is asymmetrical, with one side of the T being the long side and the other side being the short side, with unequal lengths at both ends. Electrode gaps are formed between the protruding ends of adjacent electrodes, and are divided into two types: the short sides of the two asymmetrical electrodes are arranged opposite each other, jointly forming a first electrode gap 701 with a larger width; the long sides of the symmetrical electrode and the adjacent electrode are opposite each other, jointly forming four second electrode gaps 702 with smaller widths. The first electrode gap 701 and the second electrode gap 702 form an annular gap structure.

[0013] Furthermore, each electrode support post 703 has two partially penetrated fifth threaded holes 704. A total of 12 M2 screws are used to pass through the corresponding second threaded through holes 401 on the main cavity wall 4 and then screwed into the fifth threaded holes 704 to achieve a fixed connection between the electrode 7 and the main cavity wall 4.

[0014] The rubidium atom gas chamber support 8 includes an inner ring 803, an outer ring 804, two first support protrusions 801, and four second support protrusions 802. Both the inner ring 803 and the outer ring 804 are annular thin-walled structures, coaxially placed on the same horizontal plane. The width of the first support protrusions 801 is equal to the width of the first electrode gap 701, and the width of the second support protrusions 802 is equal to the width of the second electrode gap 702. The two types of support protrusions are distributed at 60-degree intervals on the sidewall of the outer ring 803, their distribution corresponding to the distribution of the two electrode gaps, to match the annular gap structure of the electrode 7.

[0015] Furthermore, six support protrusions extend inward, connecting the inner ring 803 and the outer ring 804 of the support to form the rubidium atom gas chamber support 8. The inner diameter of the inner ring 803 is equal to the outer diameter of the gas chamber, used to fix the rubidium atom gas chamber 9. The outer diameter of the outer ring 804 should be slightly smaller than the annular gap structure formed by the electrode 7.

[0016] Furthermore, the rubidium atom gas chamber support 8 is made of Teflon material.

[0017] The coaxial cable 1 has a three-layer coaxial structure, consisting of a copper inner conductor 101, a Teflon shielding layer 102, and a copper outer conductor 103, arranged from the inside out. The inner conductor 101 is bent to form a coupling ring, constituting a magnetically excited coupling structure. This coupling ring is pre-fixed in the positioning hole 206 of the upper end cover 2. The outer conductor 103 of the copper coaxial cable has an external thread near the coupling ring. After being screwed into the pre-set sixth threaded hole 205 of the upper end cover 2, the coaxial cable 1 can be fixed to the upper end cover 2 as a whole. After assembly, the coupling ring formed by bending the inner conductor 101 of the copper coaxial cable is located at the second electrode gap 702.

[0018] A method for using a microwave resonant cavity for a compact rubidium atomic clock includes the following steps: The first step is to use M2 screws to fix six electrodes 7 to the main cavity wall 4 to form an annular electrode structure to confine the magnetic field in TE011 mode.

[0019] The second step involves inserting the cylindrical rubidium atom gas chamber 9 into the annular structure of the rubidium atom gas chamber support 8, rotating the rubidium atom gas chamber 9 to adjust its sintered structure position and place it on the side of the larger support protrusion 801, embedding the rubidium atom gas chamber support 801 into the annular gap formed by the first electrode gap 701 and the second electrode gap 702 of the electrode 7, while ensuring that the sintered structure of the rubidium atom gas chamber sidewall is in the wider first electrode gap 701, thus ensuring that the rubidium atom gas chamber is fixed in the center of the resonant cavity, and the laser can irradiate the center of the gas chamber after being refracted by the lens, exciting the rubidium atom transition.

[0020] The third step is to fix the coaxial cable 1 in the positioning hole reserved in the upper cover 2.

[0021] Fourth step: Screw the upper end cap threaded ring 3 and the lower end cap threaded ring 5 appropriately into the outer end faces of both ends of the main cavity wall 4 to limit the upper end cap 2 and the lower end cap 6. Then insert the upper end cap 2 and the lower end cap 6 into both ends of the main cavity wall 4 until the cover plate contacts the upper end cap threaded ring 3 and the lower end cap threaded ring 5. Note the fit between the protruding structure of the upper end cap 2 and the lower end cap 6 and the groove structure existing in the main cavity wall 4. After the assembly is completed, a through groove structure is formed in the cavity to improve the magnetic field distribution in TE011 mode. When the upper end cap 2 is inserted, ensure that the inner conductor 101 of the coaxial cable is within the first electrode gap 701. At this time, the normal plane of the coupling ring formed by the bending of the inner conductor is perpendicular to the magnetic field in TE011 mode to achieve a good excitation coupling effect.

[0022] Fifth step, connect the microwave transmitter power supply interface to the outer end of coaxial cable 1, rotate the upper end cover threaded ring 3 and the lower end cover threaded ring 5 to change the distance between the upper end cover 2, the lower end cover 6 and the electrode 7, adjust the cavity resonant frequency to 6.835GHz, and match the frequency of rubidium atom hyperfine transition.

[0023] The beneficial effects of this invention are as follows: (1) This invention, through the circumferentially asymmetric annular gap electrode design, enables the sintering structure of a 25mm large rubidium atom gas chamber and its sidewalls to be accommodated in a relatively small cavity, while simultaneously achieving TE 011 Miniaturization of the cavity in the mode.

[0024] (2) The present invention has a large electrode gap in the sintered structure of the large gas chamber, which will lead to a certain degradation of the field orientation factor. By designing the field through the through groove and the dual-section cavity design, the magnetic field uniformity is significantly improved, while still ensuring a high Q factor and field orientation factor, which meets the requirements of rubidium atomic clock.

[0025] (3) The present invention designs a double-end cap to compensate for the frequency shift caused by process errors by changing the distance between the end cap and the electrode, ensuring that the resonant frequency is equal to the hyperfine transition frequency of rubidium atoms. The undercoupling design of the coupling ring brings high coupling efficiency.

[0026] In summary, the above improvements contribute to the short-term frequency stability and clock signal-to-noise ratio of rubidium atomic clocks, addressing the challenges posed by traditional TE (Time-of-Flight) clocks. 011 The contradiction between miniaturization and high performance of cylindrical resonators has been addressed by providing a new design solution. Attached Figure Description

[0027] Figure 1 This is an isometric sectional view of a compact microwave resonant cavity for a rubidium atomic clock according to the present invention; Figure 2 This is a schematic diagram of the overall structure of the resonant cavity of the present invention; Figure 3 This is a schematic diagram of the lower end cap of the present invention; Figure 4 This is an axial sectional view of the cavity inside the present invention; Figure 5 This is a frontal sectional view of the cavity of the present invention; Figure 6 This is a schematic diagram of the upper end cap and coupling structure of the present invention; Figure 7 This is a schematic diagram of the coaxial cable of the present invention. Figure 8 This is a schematic diagram of the rubidium atom gas chamber support of the present invention; Figure 9 This is a schematic diagram of the upper cover of the present invention; In the diagram: 1. Coaxial cable, 2. Upper end cap, 3. Upper end cap threaded ring, 4. Main cavity wall, 5. Lower end cap threaded ring, 6. Lower end cap, 7. Electrode, 8. Rubidium atom gas chamber support, 9. Rubidium atom gas chamber; 101 Coaxial cable inner conductor (coupling ring); 102 Coaxial cable shielding layer; 103 Coaxial cable outer conductor (M6 thread at the bottom); 201 Upper end cap groove; 202 Upper end cap light-transmitting hole; 203 First threaded through hole; 204 Upper end cap protrusion; 205 Sixth threaded hole; 206 Positioning hole; 301 First threaded hole; 302 Second threaded hole; 303 First thread; 401 Second threaded through hole; 402 Main cavity wall groove; 403 Second thread line; 501 Third threaded hole; 502 Fourth threaded hole; 503 Third thread; 601 Third threaded through hole; 602 Light-transmitting hole of lower end cover; 603 Groove of lower end cover; 604 Secondary cavity; 605 Lens groove; 606 Protrusion of lower end cover; 607 Cylindrical protrusion of lower end cover; 701 First electrode gap; 702 Second electrode gap; 703 Electrode support post; 704 Fifth threaded hole (located on the electrode support post); 801 First support protrusion; 802 Second support protrusion; 803 Inner ring of support; 804 Outer ring of support. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0029] This invention provides a compact resonant cavity for rubidium atomic clocks, which is an innovative two-segment cavity and annular gap circumferential asymmetric electrode structure. It can meet the requirements of cavity miniaturization while having high Q factor, field orientation factor and coupling efficiency, and can accommodate a 25mm rubidium atomic gas cell with sidewall sintering structure.

[0030] The microwave resonant cavity includes upper and lower end caps, a coaxial cable coupling structure, cavity walls, electrodes, and a rubidium atom gas chamber support. The rubidium atom gas chamber support is made of Teflon material, the coaxial cable includes a Teflon shielding layer, and the rest of the cavity structure is CNC machined from T2 copper high conductivity material. The surface conductivity of the resonant cavity can be further improved by surface silver plating to increase the cavity Q value.

[0031] The resonant cavity structure is as follows Figure 1As shown. The microwave resonant cavity is a hollow cylindrical structure, including a coaxial cable 1, an upper end cover 2, an upper end cover threaded ring 3, a main cavity wall 4, a lower end cover threaded ring 5, a lower end cover 6, electrodes 7 located inside the main cavity wall 4, a rubidium atom gas chamber support 8, and a rubidium atom gas chamber 9. The resonant cavity body is formed by the combination of the upper end cover 2, the lower end cover 6, and the main cavity wall 4 to form a hollow cylindrical structure, defined as the cavity sealing structure and tuning structure. It contains two connected cylindrical cavities with different inner diameters. The cylindrical cavity formed by the combination of the upper end cover 2 and the main cavity wall 4 has a larger inner diameter and is defined as the main cavity. The cylindrical cavity located inside the lower end cover 6 has a smaller inner diameter and is defined as the secondary cavity 604. The upper end cover 2 and the lower end cover 6 are installed at both ends of the main cavity wall 4. The inner wall of the main cavity is provided with 6 electrodes 7, forming annular gap electrodes. The threaded mounting holes on the upper end cover 2 are used to install the coaxial cable 1. The upper end cap threaded ring 3 and the lower end cap threaded ring 5 are located at both ends of the main cavity wall 4, and are respectively locked and assembled by threaded structures to complete the cavity sealing and fixing and the resonant cavity tuning assembly and positioning.

[0032] The upper cover 2 includes an integrally formed circular cover plate and a cylindrical protrusion located inside the circular cover plate. The circular cover plate is a flat cylindrical structure, and the cylindrical protrusion extends axially from the inside of the circular cover plate. Its outer diameter is smaller than that of the circular cover plate and equal to the inner diameter of the tubular main cavity wall 4. The two are integrally formed. A through-hole 202 is provided at the center of the cylindrical structure for laser irradiation of the rubidium atom gas chamber. Next to the through-hole, a sixth threaded hole 205 and a positioning hole 206 are provided for fixing the coaxial cable 1. On the side wall of the cylindrical protrusion, thirty rectangular cross-section protrusions extending axially are distributed circumferentially, defined as upper cover protrusions 204, which correspond one-to-one with the main cavity wall grooves 402 provided axially on the side wall of the main cavity wall 4. On the end face of the cylindrical protrusion, thirty radial upper cover grooves 201 with rectangular cross-sections are provided. The upper end cover groove 201 is circumferentially distributed and its position is aligned with the upper end cover protrusion 204. The edge of the circular cover plate has six axially penetrating first threaded through holes 203. When the upper end cover 2 is assembled with the main cavity wall 4, the cylindrical protrusion of the upper end cover 2 is inserted into one end of the main cavity wall 4. The upper end cover protrusion 204 and the insertable groove 402 in the main cavity wall allow the cylindrical protrusion to be precisely embedded in the main cavity wall 4, achieving radial positioning and circumferential sealing. Simultaneously, the upper end cover groove 201 communicates with the main cavity wall groove, together forming an axially penetrating groove. The upper end cover threaded ring 3 is located inside the circular cover plate of the upper end cover 2.

[0033] In this embodiment, the rectangular cross-section protrusions are non-uniformly distributed circumferentially, totaling 30, specifically: five protrusions per group, divided into six groups; within the same group, the central angle between adjacent protrusions is 10 degrees; between two adjacent groups, i.e., between the last protrusion of the previous group and the first protrusion of the next group, the central angle is 20 degrees; the central angle is the circumferential angle formed on the radial cross-section of the cavity with the central axis of the cavity as the vertex. Multiple groups of upper end cap protrusions 204 and upper end cap grooves 201 are uniformly arranged circumferentially with a period of 60 degrees. The lower end cap 6 has a similar main structure to the upper end cap 2, but has a unique design that forms a separate secondary cavity 604. It also includes an integrally formed circular cover plate and a lower end cap cylindrical protrusion 607 located inside the circular cover plate. The cylindrical protrusion has thirty axially extending rectangular protrusions on its side, used to cooperate with the main cavity wall groove 402 axially arranged at the bottom of the main cavity wall 4. On the end face of the lower end cover 6 corresponding to the cylindrical protrusion, there are 30 radial, rectangular cross-section lower end cover grooves 603, which serve the same function as the upper end cover grooves 201. The key difference between the lower end cover 6 and the upper end cover 2 is that the central part of the inner end face of the cylindrical protrusion of the lower end cover 6 is axially cut off to form a cylindrical blind hole structure, namely the secondary cavity 604. The circular cover plate of the lower end cover 6 has six third threaded through holes 601 along the axial direction. The central part of the outer end face of the circular cover plate is axially cut off to form a blind hole structure, defined as a cylindrical lens groove 605, for installing an optical lens. A hole is drilled through the lens groove 605 and the secondary cavity 604 to form a lower end cover light-transmitting hole 602. The lower end cover threaded ring 5 is located on the inner side of the circular cover plate of the lower end cover 6. The inner diameter of the secondary cavity 604 is between the inner diameter of the main cavity wall 4 and the inner diameter of the lower end cover light-transmitting hole 602, and is used to accommodate the bulb body of the rubidium atom gas chamber 9. The lower end cover light-transmitting hole 602 has the same function as the upper end cover light-transmitting hole 202. The laser light passes through the lens groove 605, is refracted by the lens, passes through the lower end cover light-transmitting hole 602, and then irradiates the rubidium atom gas chamber before being emitted from the upper end cover light-transmitting hole 202.

[0034] The main cavity wall 4 is a tubular structure open at both ends along the axial direction. Its inner wall has thirty parallel grooves 402 that penetrate both ends axially. Five grooves form a group, creating six groups of grooves. Electrodes 7 are installed between adjacent groups of grooves on the inner wall of the main cavity wall 4, with the distribution pattern similar to the upper end cap protrusion 204. Between adjacent groups of grooves, there are two second threaded through holes 401 penetrating the main cavity wall 4 radially, used to form a threaded locking structure with the fifth threaded hole 705, fixing the electrodes 7 to the inner wall of the main cavity wall 4. Thus, multiple groups of main cavity wall grooves 402 and second threaded through holes 401 are evenly arranged circumferentially at a period of 60 degrees. Second thread lines 403 are provided on the outer wall surfaces at both the upper and lower ends of the main cavity wall 4. The cross-section of the main cavity wall grooves 402 is rectangular.

[0035] The upper end cover 2 and lower end cover 6 are connected to the main cavity wall 4 through a dual method of precision fitting and locking with threaded rings on the upper and lower end covers, ensuring the cavity's sealing and mechanical tuning functions. The upper end cover 2 and lower end cover 6 are inserted into the inner cavity of the main cavity wall 4 from both ends via rectangular protrusions on their cylindrical protrusions. The protrusions form a clearance fit with the main cavity wall groove 402, ensuring precise alignment of the upper end cover groove 201 and the lower end cover groove 603 with the main cavity wall groove 402, forming a complete through-groove structure. This design ensures the electromagnetic sealing of the cavity interior (except for the light-transmitting holes). Firstly, it ensures that the cavity has only two openings: the upper end cover light-transmitting hole 202 and the upper end cover light-transmitting hole 602, reducing unnecessary openings to guarantee the cavity's electromagnetic sealing and reduce unnecessary resonant mode interference. Simultaneously, the through-groove can constrain the magnetic field distribution within the cavity, improving the field orientation factor of the resonant cavity.

[0036] The upper end cap threaded ring 3 and the lower end cap threaded ring 5 are both circular rotating components with a rectangular cross-section. The lower end cap threaded ring 5 is thicker than the upper end cap threaded ring 3, and the other features are the same. The inner ring sidewall of the upper end cap threaded ring 3 is provided with a first thread 303, which is used to engage with the second thread 403 on the upper outer wall of the main cavity wall 4, thereby adjusting and locking the axial position of the upper end cap 2. On the end face of the upper end cap threaded ring 3, 24 first threaded holes 301 are evenly distributed circumferentially along the edge of the ring and are completely penetrating axially. The first threaded holes 301 are used to align with the fixing through holes on the edge of the upper end cap 2, and screws are screwed in to lock the upper end cap threaded ring 3 to the upper end cap 2. Between any two adjacent first threaded holes 301, there are two second threaded holes 302 with the same diameter penetrating the inner and outer outer walls of the threaded ring. After the upper end cap threaded ring 3 is screwed into the second thread line 403 along the upper outer wall of the main cavity wall 4 and adjusted to the target axial position, a set screw is screwed into the second threaded hole 302, so that the end of the screw presses against the outer wall of the main cavity wall 4, thereby fixing the upper end cap threaded ring 3 and the main cavity wall 4 relative to each other and preventing the threaded ring from rotating spontaneously and changing its axial position. Correspondingly, the inner ring side wall of the lower end cap threaded ring 5 is provided with a third thread line 503, and 24 axially penetrating third threaded holes 501 are evenly distributed on the end face. Among them, there are two fourth threaded holes 502 with the same diameter penetrating the inner and outer walls of the threaded ring between adjacent third threaded holes 501. Its structure and connection relationship are completely the same as those of the upper end cap threaded ring 3, except that the axial thickness is larger to accommodate the larger tuning distance assembly requirements of the lower end cap 6.

[0037] The resonant cavity is tuned by mechanically coupling the threads in the upper end cover threaded ring 3, the main cavity wall 4, and the lower end cover threaded ring 5, and by rotating the threaded rings to change the distance between the upper end cover 2, the lower end cover 6, and the electrode 7. The upper end cover threaded ring 3 and the lower end cover threaded ring 5 have a large number (24) of first threaded holes 301 and third threaded holes 501, allowing the minimum rotation angle of the threaded rings during tuning to be 15 degrees, thus achieving more precise tuning. The axial distance between the upper end cover 2 and the electrode 7 is closer than that between the lower end cover 6 and the electrode 7. The reasons for this design are as follows: First, the upper end cover 2 has a coupling structure; a closer axial distance ensures better coupling even in a state of undercoupling. Second, a closer axial distance between the end cover and the electrode results in higher tuning sensitivity; setting different sensitivities in the tuning structure ensures more precise and effective tuning.

[0038] Six electrodes 7 are distributed circumferentially at 60-degree intervals in the groove-free area of ​​the main cavity wall 4, forming an annular electrode structure. The six electrodes 7 are of two types: two symmetrical electrodes and four asymmetrical electrodes. The two symmetrical electrodes are arranged adjacently, and the four asymmetrical electrodes are arranged adjacently, specifically: a first symmetrical electrode, a second symmetrical electrode, a first asymmetrical electrode, a second asymmetrical electrode, a third asymmetrical electrode, and a fourth asymmetrical electrode. Both types of electrodes are columnar structures formed by axial stretching of a T-shaped cross-section. Each electrode 7 has an electrode support column 703 integrally connected to its outer side. The T-shaped structure of the symmetrical electrode is planar symmetrical, with equal lengths at both ends of the T. The T-shaped structure of the asymmetrical electrode is asymmetrical, with one side of the T being the long side and the other side being the short side, with unequal lengths at both ends. Electrode gaps are formed between the protruding ends of adjacent electrodes, and are divided into two types: the short sides of the two asymmetrical electrodes are arranged opposite each other, jointly forming a first electrode gap 701 with a larger width; the long sides of the symmetrical electrode and the adjacent electrode are opposite each other, jointly forming four second electrode gaps 702 with smaller widths. The first electrode gap 701 and the second electrode gap 702 form an annular gap structure. The purpose of setting different electrode gap sizes is to accommodate the fused sintered structure of the gas chamber sidewall while improving the Q factor of the cavity. Increasing the electrode gap size significantly increases the resonant frequency of the resonant cavity and decreases the Q factor, while increasing the electrode thickness decreases the resonant frequency. To achieve a reasonable electrode thickness, maintaining a compact design while ensuring a high Q factor, the above design is adopted. Ultimately, a field orientation factor of over 0.9 and a loaded Q value of over 180 can be achieved.

[0039] In this embodiment, each electrode support post 703 has two partially penetrating fifth threaded holes 704. A total of 12 M2 screws are used to pass through the corresponding second threaded through holes 401 on the main cavity wall 4 and then screwed into the fifth threaded holes 704 to achieve a fixed connection between the electrode 7 and the main cavity wall 4. The fifth threaded holes 704 are non-penetrating threaded holes to maintain the integrity of the inner surface of the electrode, thereby improving the Q value of the resonant cavity.

[0040] In this embodiment, the rubidium atom gas chamber support 8 includes an inner ring 803, an outer ring 804, two first support protrusions 801, and four second support protrusions 802. Both the inner ring 803 and the outer ring 804 are annular thin-walled structures, coaxially placed on the same horizontal plane. The width of the first support protrusions 801 is equal to the width of the first electrode gap 701, and the width of the second support protrusions 802 is equal to the width of the second electrode gap 702. The two types of support protrusions are distributed at 60-degree intervals on the sidewall of the outer ring 803, their distribution corresponding to the distribution of the two electrode gaps, to match the annular gap structure of the electrode 7.

[0041] In this embodiment, six support protrusions extend inward, connecting the inner ring 803 and the outer ring 804 of the support to form a rubidium atom gas chamber support 8. The inner diameter of the inner ring 803 is equal to the outer diameter of the gas chamber, used to fix the rubidium atom gas chamber 9. The outer diameter of the outer ring 804 should be slightly smaller than the annular gap structure formed by the electrode 7, so that the support can be easily embedded into the annular gap structure of the electrode 7 during installation.

[0042] In this embodiment, the rubidium atom gas chamber support 8 is made of Teflon. Since the support is located between the electrodes, it inevitably affects the relative permittivity and relative permeability of the medium within the chamber. Therefore, Teflon is used and a perforated structure is designed to reduce the influence of the support on the magnetic field distribution.

[0043] In this embodiment, the coaxial cable 1 has a three-layer coaxial structure, consisting of a copper coaxial cable inner conductor 101, a Teflon coaxial cable shielding layer 102, and a copper coaxial cable outer conductor 103, arranged from the inside out. The inner conductor 101 is bent to form a coupling ring, constituting a magnetically excited coupling structure. The coupling ring is pre-fixed in the positioning hole 206 of the upper end cover 2. The outer conductor 103 of the copper coaxial cable has an external thread near the coupling ring. After being screwed into the sixth threaded hole 205 pre-set in the upper end cover 2, the coaxial cable 1 can be fixed to the upper end cover 2 as a whole. After assembly, the coupling ring formed by bending the inner conductor 101 of the copper coaxial cable is located at the second electrode gap 702. By reasonably designing the area and depth of the coupling ring, a high coupling efficiency is achieved in a sub-coupling manner, and the S11 reflection coefficient can be reduced to -8.

[0044] In this embodiment, a two-segment design of the resonant cavity wall is used. Under these design parameters, to balance the Q-factor degradation and the influence of miscellaneous modes caused by electrode asymmetry, the length of electrode 7 is shortened to reduce the frequency of low-frequency high-order miscellaneous modes, thus improving TE. 011The mode is pure and free from extraneous mode interference, ensuring good field orientation factor and magnetic field uniformity. Secondly, shortening the electrodes reduces the current integration area within the cavity, improving the cavity Q-factor. To address the increased distance to the end cap and decreased tuning sensitivity caused by shortening the electrodes, a two-segment cavity wall design is adopted. The main cavity wall 4 houses the electrodes 7 and the rubidium atom gas chamber support 8, while the secondary cavity wall 604 is only large enough to accommodate the rubidium atom gas chamber. This structure leads to a decrease in the field orientation factor; however, by incorporating a through-groove design in the main cavity wall 4, the field orientation factor can still be maintained above 0.9.

[0045] The examples described above 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 compact microwave resonant cavity for a rubidium atomic clock, characterized in that, The microwave resonant cavity is a hollow cylindrical structure, including a coaxial cable (1), an upper end cover (2), an upper end cover threaded ring (3), a main cavity wall (4), a lower end cover threaded ring (5), a lower end cover (6), an electrode (7) located inside the main cavity wall (4), a rubidium atom gas chamber support (8), and a rubidium atom gas chamber (9). The resonant cavity is a hollow cylindrical structure formed by the combination of an upper end cover (2), a lower end cover (6), and a main cavity wall (4). It is defined as a cavity sealing structure and a tuning structure. It contains two connected cylindrical cavities with different inner diameters. The cylindrical cavity formed by the combination of the upper end cover (2) and the main cavity wall (4) has a larger inner diameter and is defined as the main cavity. The cylindrical cavity located inside the lower end cover (6) has a smaller inner diameter and is defined as the secondary cavity (604). The upper end cover (2) and the lower end cover (6) are installed on... The main cavity wall (4) has six electrodes (7) on its inner wall, forming annular gap electrodes. The rubidium atom gas chamber (9) is fixed in the resonant cavity by the rubidium atom gas chamber bracket (8). The upper end cover (2) has a threaded mounting hole for installing a coaxial cable (1). The upper end cover threaded ring (3) and the lower end cover threaded ring (5) are located at both ends of the main cavity wall (4) and are respectively locked and assembled by the threaded structure to complete the cavity sealing and fixing and the resonant cavity tuning assembly and positioning. Six electrodes (7) are distributed circumferentially at 60-degree intervals in the groove-free area of ​​the main cavity wall (4), together forming an annular electrode structure.

2. The microwave resonant cavity for a compact rubidium atomic clock according to claim 1, characterized in that, The upper end cover (2) includes an integrally formed circular cover plate and a cylindrical protrusion located inside the circular cover plate. The cylindrical protrusion extends axially from the inside of the circular cover plate, and its outer diameter is smaller than the outer diameter of the circular cover plate and equal to the inner diameter of the tubular main cavity wall (4). The two are integrally formed. The upper end cover threaded ring (3) is located inside the circular cover plate of the upper end cover (2). The upper end cover (2) has a through-hole (202) at its center for laser irradiation of the rubidium atom gas chamber (9). The upper end cover (2) also has a sixth threaded hole (205) and a positioning hole (206) for fixing the coaxial cable (1). The cylindrical protruding sidewall has thirty rectangular cross-section protrusions extending axially along the circumference, defined as upper end cover protrusions (204), which correspond one-to-one with the axially arranged main cavity wall grooves (402) on the sidewall of the main cavity wall (4). On the protruding end face, there are thirty radial grooves (201) with rectangular cross sections for the upper end cover; the grooves (201) are distributed circumferentially and their positions are aligned with the upper end cover protrusions (204); the edge of the circular cover plate is provided with six axially penetrating first threaded through holes (203); when the upper end cover (2) is assembled with the main cavity wall (4), radial positioning and circumferential sealing are achieved, and at the same time, the grooves (201) of the upper end cover are connected with the grooves (402) of the main cavity wall, which together form an axially penetrating groove; The lower end cover (6) has a similar main structure to the upper end cover (2). The threaded ring (5) of the lower end cover is located inside the circular cover plate of the lower end cover (6). Specifically, the lower end cover (6) also includes an integrally formed circular cover plate and a lower end cover cylindrical protrusion (607) located inside the circular cover plate. The cylindrical protrusion has thirty axially extending rectangular convex strips on its side surface, which are used to cooperate with the groove (402) of the main cavity wall. On the end face of the lower end cover (6), there are 30 radial, rectangular lower end cover grooves (603). The side wall of the lower end cover cylindrical protrusion (607) has thirty axially extending rectangular cross-section convex strips distributed circumferentially, which are defined as lower end cover convex strips (606). The lower end cover (6) and the upper end cover (2) have similar main structures. The key difference of the end cap (2) is that the central part of the inner end face of the cylindrical protrusion of the lower end cap (6) is axially cut off to form a cylindrical blind hole structure, namely the secondary cavity (604); the circular cover plate is provided with six third threaded through holes (601) along the axial direction, and the central part of the outer end face of the circular cover plate is axially cut off to form a blind hole structure, which is defined as the lens groove (605) for installing optical lenses. The lens groove (605) and the secondary cavity (604) are drilled through to form the light-transmitting hole (602) of the lower end cap; the laser passes through the lens groove (605), is refracted by the lens, and then passes through the light-transmitting hole (602) of the lower end cap to irradiate the rubidium atom gas chamber (9) and is emitted from the light-transmitting hole (202) of the upper end cap.

3. The compact microwave resonant cavity for a rubidium atomic clock according to claim 2, characterized in that, The upper end cover protrusion (204) is specifically as follows: The rectangular cross-section protrusions are non-uniformly distributed along the circumference, totaling 30. Specifically, they are divided into six groups of five protrusions each. Within the same group, the central angle between adjacent protrusions is 10 degrees. The central angle between two adjacent groups, i.e., between the last protrusion of the previous group and the first protrusion of the next group, is 20 degrees. The central angle is the circumferential angle formed on the radial cross-section of the cavity with the central axis of the cavity as the vertex. The multiple groups of upper end cap protrusions (204) and upper end cap grooves (201) are uniformly arranged along the circumference with a period of 60 degrees.

4. The microwave resonant cavity for a compact rubidium atomic clock according to claim 2, characterized in that, The inner diameter of the secondary cavity (604) is between the inner diameter of the main cavity wall (4) and the inner diameter of the light-transmitting hole (602) of the lower end cover, and is used to accommodate the bulb body of the rubidium atom gas chamber (9).

5. A compact microwave resonant cavity for a rubidium atomic clock according to claim 4, characterized in that, The main cavity wall (4) is a tubular structure with openings at both ends in the axial direction. Thirty parallel grooves (402) are provided on its inner wall, which run through both ends in the axial direction. Five grooves form a group, forming six groups of grooves. Electrodes (7) are installed between two adjacent groups of grooves on the inner wall of the main cavity wall (4). Their distribution is the same as that of the upper end cap protrusion (204). Between two adjacent groups of grooves, there are two second threaded through holes (401) that run through the main cavity wall (4) in the radial direction. These holes are used to form a threaded locking structure with the fifth threaded hole (705) to fix the electrodes (7) to the inner wall of the main cavity wall (4). Second thread lines (403) are provided on the outer wall surfaces at both the upper and lower ends of the main cavity wall (4). The upper end cover (2), lower end cover (6) and main cavity wall (4) are connected by a dual method of precision fitting and locking with threaded rings of the upper and lower end covers, ensuring the cavity's sealing and mechanical tuning function, and guaranteeing the electromagnetic sealing of the cavity.

6. The microwave resonant cavity for a compact rubidium atomic clock according to claim 5, characterized in that, The upper end cap threaded ring (3) and the lower end cap threaded ring (5) are both circular rotating components with a rectangular cross-section. The thickness of the lower end cap threaded ring (5) is greater than that of the upper end cap threaded ring (3), and the other features of the two are the same. Specifically: The inner ring sidewall of the upper end cap threaded ring (3) is provided with a first thread (303) for engaging with the second thread (403) on the upper outer wall of the main cavity wall (4) to adjust and lock the axial position of the upper end cap (2). On the end face of the upper end cap threaded ring (3), 24 first threaded holes (301) are evenly distributed circumferentially along the edge of the ring and are completely penetrating axially for screwing in screws to lock the upper end cap threaded ring (3) and the upper end cap (2). Between any two adjacent first threaded holes (301), two through-threaded rings are provided along the same diameter. The second threaded hole (302) of the wall; after the upper end cap threaded ring (3) is screwed in along the second thread line (403) and adjusted to the target axial position, the set screw is screwed into the second threaded hole (302) to achieve relative fixation between the upper end cap threaded ring (3) and the main cavity wall (4); correspondingly, the inner ring side wall of the lower end cap threaded ring (5) is provided with a third thread line (503), and 24 axially penetrating third threaded holes (501) are evenly distributed on the end face, among which two fourth threaded holes (502) with the same diameter penetrating the inner and outer walls of the threaded ring are provided between adjacent third threaded holes (501).

7. A compact microwave resonant cavity for a rubidium atomic clock according to claim 6, characterized in that, The six electrodes (7) are divided into two types: two are symmetrical electrodes and four are asymmetrical electrodes. The two symmetrical electrodes are arranged adjacent to each other, and the four asymmetrical electrodes are arranged adjacent to each other, including the first symmetrical electrode, the second symmetrical electrode, the first asymmetrical electrode, the second asymmetrical electrode, the third asymmetrical electrode, and the fourth asymmetrical electrode. Both types of electrodes are columnar structures formed by stretching a T-shaped cross section along the axial direction. Each electrode (7) is integrally connected to an electrode support column (703) on its outer side. An electrode gap is formed between the protruding ends of two adjacent electrodes. There are two types: the short sides of the two asymmetrical electrodes are arranged opposite each other, forming a first electrode gap (701) with a large width. The long sides of the symmetrical electrode and the adjacent electrode are opposite each other, forming four second electrode gaps (702) with a small width. The first electrode gap (701) and the second electrode gap (702) form an annular gap structure. Each electrode support post (703) has two partially penetrated fifth threaded holes (704). After the screw passes through the second threaded through hole (401) on the main cavity wall (4), it is screwed into the fifth threaded hole (704) to achieve a fixed connection between the electrode (7) and the main cavity wall (4).

8. A compact microwave resonant cavity for a rubidium atomic clock according to claim 7, characterized in that, The rubidium atom gas chamber support (8) includes an inner ring (803), an outer ring (804), two first support protrusions (801), and four second support protrusions (802). The inner ring (803) and the outer ring (804) are both annular thin-walled structures, coaxially placed on the same horizontal plane. The width of the first support protrusion (801) is equal to the width of the first electrode gap (701), and the width of the second support protrusion (802) is equal to the width of the second electrode gap (702). The two types of support protrusions are distributed on the side wall of the outer ring (803), and their distribution pattern corresponds to the distribution of the two types of electrode gaps to match the annular gap structure of the electrode (7). Six support protrusions extend inward to connect the inner ring (803) of the support with the outer ring (804) of the support, forming a rubidium atom gas chamber support (8) for fixing the rubidium atom gas chamber (9).

9. A compact microwave resonant cavity for a rubidium atomic clock according to claim 8, characterized in that, The coaxial cable (1) has a three-layer coaxial structure, consisting of a copper coaxial cable inner conductor (101), a Teflon coaxial cable shielding layer (102), and a copper coaxial cable outer conductor (103) from the inside out. The inner conductor (101) of the coaxial cable is bent to form a coupling ring, which constitutes a magnetic excitation coupling structure. The coupling ring is pre-fixed in the positioning hole (206) of the upper end cover (2). After assembly, the coupling ring is located at the second electrode gap (702). The outer conductor (103) of the copper coaxial cable has an external thread at one end near the coupling ring. After being screwed into the fifth threaded hole (205) of the upper end cover (2), the coaxial cable (1) is fixed to the upper end cover (2) as a whole.

10. A method of using the microwave resonant cavity for a compact rubidium atomic clock as described in any one of claims 1-9, characterized in that, Includes the following steps: The first step is to fix six electrodes (7) in the main cavity wall (4) to form an annular electrode structure; The second step is to insert the cylindrical rubidium atom gas chamber (9) into the annular structure of the rubidium atom gas chamber support (8), rotate the rubidium atom gas chamber (9) to adjust its sintering structure position and place it on the side of the support protrusion (801), embed the rubidium atom gas chamber support (8) 01 into the annular gap formed by the first electrode gap (701) and the second electrode gap (702) of the electrode (7), and fix the rubidium atom gas chamber (9) in the center of the resonant cavity. The laser is refracted by the lens and irradiated into the center of the gas chamber to excite the rubidium atom transition. The third step is to fix the coaxial cable (1) in the positioning hole (206) reserved in the upper end cover (2); Fourth step, screw the upper end cap threaded ring (3) and the lower end cap threaded ring (5) into the outer end faces of both ends of the main cavity wall (4) to limit the upper end cap (2) and the lower end cap (6). Then insert the upper end cap (2) and the lower end cap (6) into both ends of the main cavity wall (4) until the cover plate contacts the upper end cap threaded ring (3) and the lower end cap threaded ring (5). After the assembly is completed, a through groove structure is formed in the cavity. When the upper end cap (2) is inserted, ensure that the conductor (101) inside the coaxial cable is inside the first electrode gap (701). At this time, the normal plane of the coupling ring is perpendicular to the magnetic field in the TE011 mode. Fifth step, connect the microwave transmitter power supply interface to the outer end of the coaxial cable (1), rotate the upper end cover threaded ring (3) and the lower end cover threaded ring (5) to change the distance between the upper end cover (2), the lower end cover (6) and the electrode (7), adjust the cavity resonant frequency, and match the frequency of the hyperfine transition of rubidium atoms.

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