High q value frequency tunable sapphire microwave cavity

Abstract

The application discloses a high-Q-value frequency tunable sapphire microwave cavity, which comprises a metal shielding cavity, a sapphire crystal, a sapphire crystal fixing screw, a sapphire crystal fixing bolt, a coupling device, a dielectric crystal, a dielectric crystal fixing screw and a dielectric crystal fixing bolt, wherein the metal shielding cavity is made of copper, aluminum or other metals; the sapphire crystal is fixed on one side end cover of the metal shielding cavity through the sapphire crystal fixing screw and the sapphire crystal fixing bolt; the coupling device comprises a coupling probe or a coupling ring and is fixed on the side wall and the end cover of the metal shielding cavity and is used for input and output coupling of microwave energy; the dielectric crystal is fixed on the other side end cover of the metal shielding cavity through the fixing screw and the fixing bolt, the depth of the dielectric crystal into the cavity is adjustable, and the dielectric crystal is fastened through the fixing bolt. The high-Q-value frequency tunable sapphire microwave cavity can realize frequency tuning of the microwave cavity and can maintain and optimize the Q value of the microwave cavity.

Description

Technical Field

[0001] This invention relates to the field of microwave cavity technology, and more particularly to a high-Q-value frequency-tunable sapphire microwave cavity. Background Technology

[0002] Low-phase-noise, high-stability microwave frequency sources are widely used in radar, communications, aerospace, metrology, and fundamental physics research. Currently, microwave sources are mainly obtained in two ways: 1. Traditionally, by frequency doubling a standard crystal oscillator (5MHz or 10MHz). 2. By designing the resonant frequency of a dielectric oscillator (DRO) and using external circuitry. Compared to these two traditional methods, low-temperature sapphire microwave frequency sources exhibit extremely low phase noise (<-160dBc / Hz@10kHz in the X-band) and excellent short-term stability (<1E-15@1s), performance far exceeding that of traditional microwave sources. A high-Q microwave cavity is the core component of a high-performance microwave frequency source, reducing phase noise and improving stability. Currently, both high-stability, high-phase-noise low-temperature sapphire microwave sources and ordinary dielectric oscillators (DROs) utilize high-Q microwave cavities. The Q value of the microwave cavity used in low-temperature sapphire microwave sources reaches E8, while that used in ordinary DROs is around E5. To achieve high performance, the microwave cavity in the low-temperature sapphire microwave frequency source operates in whispering-gallery mode. This mode is a high-order mode, and many closely spaced high-order modes and cavity modes exist nearby; these modes are collectively referred to as stray modes. Due to the high mode density, the frequency sensitivity and Q-value of the stray modes themselves can affect the performance of nearby target whispering-gallery modes, thereby reducing their performance. Since the resonant frequency is determined by the dielectric constant and physical dimensions of the dielectric material, once the cavity dimensions are fixed, the resonant frequency is also determined. Summary of the Invention

[0003] This invention provides the following technical solution:

[0004] This specification provides a high-Q frequency-tunable sapphire microwave cavity, including a metal shielded cavity, a sapphire crystal, sapphire crystal fixing screws, sapphire crystal fixing bolts, a coupling device, a dielectric crystal, dielectric crystal fixing screws, and dielectric crystal fixing bolts, wherein:

[0005] The metal shielding cavity is made of copper and aluminum. The sapphire crystal is fixed to one end cover of the metal shielding cavity by sapphire crystal fixing screws and sapphire crystal fixing bolts. The coupling device includes a coupling probe or coupling ring, which is fixed to the side wall and end cover of the metal shielding cavity for microwave energy input and output coupling. The dielectric crystal is fixed to the other end cover of the metal shielding cavity by fixing screws and fixing bolts. Its insertion depth into the cavity is adjustable and it is tightened by fixing bolts.

[0006] This invention utilizes a dielectric crystal sheet in conjunction with a sapphire crystal to adjust the position of the dielectric crystal sheet relative to the sapphire crystal, thereby achieving microwave cavity resonant frequency adjustment. During the resonant frequency adjustment process, the target whispering-gallery mode can be adjusted away from spurious modes as needed, significantly reducing the impact of spurious modes on the Q-value of the target whispering-gallery mode, thus optimizing the Q-value of the microwave cavity.

[0007] Compared to electrically controlled frequency-tuned microwave cavities, which introduce a metal layer bonded to the crystal, this invention increases microwave losses in the dielectric crystal and affects the cavity's Q-value, making it unsuitable for high-Q sapphire microwave cavities. This invention, however, achieves microwave cavity frequency tuning while maintaining and optimizing the microwave cavity's Q-value.

[0008] This microwave cavity uses a dielectric crystal plate in conjunction with a sapphire crystal to achieve cavity resonant frequency adjustment. The dielectric crystal plate affects the evanescent field outside the sapphire crystal; adjusting the position of the dielectric crystal plate relative to the sapphire crystal allows for adjustment of the microwave cavity resonant frequency. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of a high-Q-value frequency-tunable sapphire microwave cavity according to an embodiment of the present invention.

[0010] Figure 2 This is a top view of the dielectric crystal in an embodiment of the present invention.

[0011] Reference numerals: 1. Metal shielding cavity; 2. Sapphire crystal; 3. Sapphire crystal fixing screw; 4. Sapphire crystal fixing bolt; 5. Coupling device; 6. Dielectric crystal; 7. Dielectric crystal fixing screw; 8. Dielectric crystal fixing bolt.

[0012] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this specification clearer, the technical solutions of this specification will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this specification, and not all of them. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this specification.

[0014] As described herein, the term “comprising” and its various variations can be understood as open-ended terms that mean “including but not limited to”, and the term “one embodiment” can be understood as “at least one embodiment”.

[0015] Figure 1 The schematic diagram illustrates the structure of a high-Q frequency-tunable sapphire microwave cavity according to an embodiment of this application, including: a metal shielding cavity 1, a sapphire crystal 2, a sapphire crystal fixing screw 3, a sapphire crystal fixing bolt 4, a coupling device 5, a dielectric crystal 6, a dielectric crystal fixing screw 7, and a dielectric crystal fixing bolt 8.

[0016] When using, follow Figure 1 Installation is then carried out. The metal shielding cavity can be made of metals such as copper and aluminum. To improve surface conductivity, surface plating such as gold or silver, or polishing, can also be applied. The sapphire crystal 2 is fixed to one end cap of the metal shielding cavity using sapphire crystal fixing screws 3 and sapphire crystal fixing bolts 4. The coupling device 5 typically includes a coupling probe or coupling ring, fixed to the side wall and end cap of the metal shielding cavity 1, used for microwave energy input / output coupling. The dielectric crystal 6 is fixed to the other end cap of the metal shielding cavity using fixing screws 7 and fixing bolts 8. Its insertion depth is adjustable and can be tightened using fixing bolts. The cross-section of the dielectric crystal is shown below. Figure 1 As shown, the top view is as follows Figure 2 As shown, the dielectric crystal 6 has a convex disc shape with the same overall diameter as the sapphire crystal 2. The convex portion is used to couple microwave energy near the sapphire crystal 2, thereby affecting the evanescent field outside the sapphire crystal 2 and thus changing the whispering-gallery mode frequency. The convex portion of the dielectric crystal 6 is designed with an irregular shape, consisting of three convex rings when viewed from the side. This shape represents a three-stage coupling design. Compared to a single-stage coupling design, three-stage coupling reduces the influence of the dielectric crystal's own mode on the whispering-gallery mode Q-value. Adjusting the cavity depth of the dielectric crystal, i.e., adjusting the value of x, allows for adjustment of the coupling amount, thereby adjusting the whispering-gallery mode frequency of the microwave cavity.

[0017] The dielectric crystal 6 can be fixed in various ways, including but not limited to using fixing screws and bolts. It can also be equipped with devices such as motors to achieve adjustment of the insertion depth.

[0018] The dielectric crystal 6 includes, but is not limited to, the use of sapphire crystal.

[0019] Based on simulation results, the sapphire crystal has a diameter of 30mm and a height of 50mm. The dielectric crystal is also sapphire. The overall diameter of the dielectric crystal is l1 (30mm), l2 (26mm), and l3 (24mm). The overall height of the dielectric crystal is h1 (12mm), the height of the protruding portion is h2 (8mm), and the thickness of the protruding ring on the side is h3 (2mm).

[0020] Install the sapphire crystal, coupling device, and dielectric crystal as shown in the diagram. Use a vector network analyzer to connect the coupling device and test the whispering gallery mode to find the target whispering gallery mode and nearby cavity higher-order modes. For example, if the mode frequency is 9.211 GHz and the Q value is 8.9E8, there are cavity higher-order modes within a 30 MHz range, with frequencies of 9.210 GHz and Q values ​​of 3E7.

[0021] By adjusting the cavity depth of the dielectric crystal and using a vector network analyzer to test the frequency of the target whispering mode and the higher-order modes of the nearby cavity, the frequency of the target whispering mode is adjusted to an appropriate position that is not affected by the higher-order modes of the cavity. For example, adjusting it to 9.205 GHz can make the target whispering mode unaffected by the higher-order modes of the cavity. After testing, the Q value of the target whispering mode is still 8.9E8 at this time, and it is not affected by the frequency adjustment.

[0022] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0023] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A high Q-value frequency tunable sapphire microwave cavity, characterized in that, The microwave cavity comprises a metal shielding cavity, a sapphire crystal, a sapphire crystal fixing screw, a sapphire crystal fixing bolt, a coupling device, a dielectric crystal, a dielectric crystal fixing screw, and a dielectric crystal fixing bolt. The metal shielding cavity is made of copper or aluminum, the sapphire crystal is fixed on one side end cover of the metal shielding cavity through the sapphire crystal fixing screw and the sapphire crystal fixing bolt, the coupling device comprises a coupling probe or a coupling ring and is fixed on the side wall and the end cover of the metal shielding cavity for input and output coupling of microwave energy, and the dielectric crystal is fixed on the other side end cover of the metal shielding cavity through the fixing screw and the fixing bolt and has an adjustable depth into the cavity and is fastened through the fixing bolt. The dielectric crystal is in the shape of a disc with a protruding edge, has the same overall diameter as the sapphire crystal, and the protruding edge of the dielectric crystal is designed to be shaped as a special shape, which comprises three protruding circular rings when viewed from the side, and the shape is a three-stage coupling design. The sapphire crystal has a size of 30 mm in diameter and 50 mm in height, the dielectric crystal is also a sapphire crystal, the overall diameter l1 of the dielectric crystal is 30 mm, the second diameter l2 is 26 mm, the third diameter l3 is 24 mm, the overall height h1 of the dielectric crystal is 12 mm, the height h2 of the protruding part is 8 mm, and the thickness h3 of the side protruding circular ring is 2 mm.

2. The microwave cavity of claim 1, wherein The coupling device is connected to a vector network analyzer to test the whispering gallery mode, find the target whispering gallery mode and the nearby cavity high-order mode, the mode frequency is 9.211 GHz, the Q value is 8.9E8, and within a range of 30 MHz near the target whispering gallery mode, there are cavity high-order modes, respectively: frequency 9.210 GHz, Q value 3E7.

3. The microwave cavity of claim 1, wherein The depth of the dielectric crystal into the cavity is adjusted, the frequency of the target whispering gallery mode and the nearby cavity high-order mode is tested by the vector network analyzer, and the frequency of the target whispering gallery mode is adjusted to an appropriate position that is not affected by the cavity high-order mode.

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