Trapped wave device for inhibiting microwave leakage of magnetron

Abstract

The invention discloses a notch device for suppressing microwave leakage of a magnetron, which is characterized in that equivalent capacitance is formed by grooving the surface of an outer conductor of a coaxial waveguide, and a non-ideal parallel resonance circuit is constructed by combining an inductive effect formed between an inner conductor and an outer conductor in a signal transmission process and equivalent resistance formed by introducing an attenuation ceramic ring. And when the transmission signal frequency is matched with the resonant frequency, a notch effect is formed. The two trap circuits which are relatively independent are adopted, attenuation of second harmonics larger than 10 dB can be achieved, and meanwhile additional suppression is provided for fundamental waves. The structure is excellent in high temperature resistance, meets the pipe manufacturing environment of 500 DEG C or above, and can work at 200 DEG C for a long time.

Description

Technical Field

[0001] This invention relates to the field of signal processing technology, and in particular to a notch filter device for suppressing microwave leakage from a magnetron. Background Technology

[0002] A 15kW continuous wave magnetron operating in the 2450 ±20MHz frequency band has microwave energy leakage at its cathode high-voltage lead, posing the following risks: 1) Equipment reliability risk: The measured fundamental frequency leakage power at the lead port is accompanied by second harmonic (4900 MHz) leakage; strong microwave energy coupling to the high-voltage power supply line causes abnormal temperature rise of rectifier devices and dielectric breakdown of filter capacitors, significantly shortening the equipment lifespan. 2) Electromagnetic compatibility failure: The 4900 MHz harmonic overlaps with the 5G n78 frequency band (3300-4900MHz) and the WLAN 5 GHz channel; in industrial scenarios with multiple device clusters, the coherent superposition of harmonic leakage can increase background noise, causing a decrease in the receiving sensitivity of 5G base stations. Currently, the industry generally uses λ / 4 chokes to suppress only the fundamental frequency, or broadband absorption methods to absorb both the fundamental and second harmonics. Both of these methods have inherent defects, specifically: a) Insufficient second harmonic suppression: The physical length of the λ / 4 choke is determined by the fundamental wavelength (L=λ / 4≈30 mm), exhibiting low impedance characteristics for second harmonic signals, resulting in insufficient suppression efficiency for the 4900MHz harmonic. b) Thermal management bottleneck: Existing broadband absorption methods (such as ferrite beads) experience localized overheating due to dielectric loss under continuous operation at 15kW. Thermal management failure triggers a triple vicious cycle: heat source superposition effect (self-heating of the absorber, cathode heat conduction), accelerated material aging (decreased permeability, dielectric constant drift, oxidation of the absorber), and system cascading failures (thermal runaway, insulation failure). Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a notch filter device for suppressing microwave leakage from a magnetron. While retaining the high-efficiency fundamental wave suppression characteristics of the λ / 4 choke sleeve, it achieves quasi-lossless passage of the second harmonic through a gradual characteristic impedance design, while meeting the requirements of industrial-grade thermal stability and space constraints.

[0004] Technical solution: A notch filter device for suppressing microwave leakage of a magnetron, comprising an inner conductor, an attenuating ceramic ring, and an outer conductor arranged sequentially from the inside to the outside, with a notch groove provided on the outer conductor; The inner conductor is the high-voltage lead of one end electrode of the magnetron cathode; The outer conductor is the high-voltage lead of the other electrode of the magnetron cathode, and the central axis of the outer conductor coincides with the central axis of the inner conductor; The central axis of the attenuation ceramic ring coincides with the central axis of the inner conductor, and the outer diameter is the same as the inner diameter of the outer conductor, while the inner diameter is the same as the outer diameter of the inner conductor. The notch groove can achieve equivalent capacitance, and the attenuating ceramic ring placed between the inner and outer conductors can achieve equivalent resistance. Under the effect of equivalent inductance and equivalent capacitance, combined with the magnetic field formed during the axial transmission of TEM electromagnetic waves, an inductive effect is formed, forming a non-ideal parallel resonant circuit. When the frequency of the transmitted signal is the same as the resonant frequency of the resonant circuit, a notch circuit is formed.

[0005] Furthermore, the surface of the outer conductor is provided with two symmetrically arranged notch grooves, each notch groove including a first groove and four trapezoidal grooves; the first groove is a rectangular groove parallel to the central axis, and one side of the first groove is provided with a mirror-arranged first trapezoidal groove and a fourth trapezoidal groove, and the other side of the first groove is provided with a mirror-arranged second trapezoidal groove and a third trapezoidal groove; the first trapezoidal groove and the second trapezoidal groove are located on both sides of the first groove and are arranged symmetrically, and the third trapezoidal groove and the fourth trapezoidal groove are located on both sides of the first groove and are arranged symmetrically; the included angle between the first trapezoidal groove and the second trapezoidal groove is θ≥0°.

[0006] Furthermore, the distance between the first trapezoidal groove and the fourth trapezoidal groove is the same as the side length of the attenuation ceramic ring.

[0007] Furthermore, the attenuation ceramic ring is cylindrical, with its two end faces parallel, and the angle between each end face and the central axis is [value missing]. >0°, the two ends of the central hole of the attenuation ceramic ring are chamfered.

[0008] Furthermore, the resonant frequency of a customized notch circuit can be achieved by changing the shape of the notch groove to alter the equivalent capacitance, or by changing the dielectric constant of the attenuating ceramic ring to alter the equivalent resistance. Alternatively, the bandwidth and attenuation depth of a customized notch filter circuit can be achieved by changing the loss tangent of the attenuation ceramic ring.

[0009] Compared with the prior art, the significant advantages of this invention are as follows: 1. The notch filter of the present invention can generate a bandwidth of 4900 ±60MHz covering the frequency band of the second harmonic signal of 4900 ±40MHz by constructing the equivalent capacitance and equivalent inductance according to the frequency of the transmitted signal. 2. The notch filter of the present invention can achieve a wider operating frequency band by adjusting the loss tangent of the attenuation ceramic ring. While attenuating the second harmonic power, it can further suppress the fundamental power by about 7dB. 3. In this invention, the inner conductor, outer conductor, and attenuation ceramic ring constituting the notch filter device can all withstand high temperatures above 500°C, meeting the temperature and insulation requirements during the magnetron tube tube process, and can operate at 200°C for a long time, meeting the requirements of the magnetron for long-term operation of the notch filter circuit. Attached Figure Description

[0010] Figure 1A technical roadmap for suppressing microwave leakage using a hybrid structure of coaxial cavity + notch filter circuit; Figure 2 The circuit diagram of the non-ideal parallel resonant circuit corresponding to the notch filter; Figure 3 This is a schematic diagram of the notch filter's external shape. Figure 4 This is an axial cross-sectional view of two independent notch circuits; Figure 5 This is a schematic diagram of the groove structure of the outer conductor, where (a) is the front view and (b) is the right view; Figure 6 This is a schematic diagram of the three-dimensional structure of the attenuation ceramic ring, where (a) is the front view and (b) is the right view; Figure 7 The simulation diagram shows the S11 effect of the notch filter circuit, where the S11 value of the second harmonic 4900 ± 40 MHz is less than -11 dB; Figure 8 The simulation diagram of S21 for the notch filter circuit is shown, where the S21 value of the second harmonic 4900 ±40 MHz is less than -10dB; Figure 9 With a notch filter, the S21 value of the fundamental frequency 2450 ± 20 MHz is less than -43 dB; Figure 10 Without a notch filter, the S21 value of the fundamental frequency 2450 ± 20 MHz is less than -36 dB. Detailed Implementation

[0011] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0012] Figure 1 This is a schematic diagram of the technical route for suppressing microwave leakage using a hybrid structure filter of coaxial cavity + notch filter circuit.

[0013] This embodiment provides a notch filter for suppressing microwave leakage using a 15 kW magnetron in a continuous wave band with a frequency of 2450 ± 20 MHz (corresponding to a second harmonic frequency of 4900 ± 40 MHz). It achieves an equivalent capacitance effect by designing a appropriately sized slot structure on the outer conductor of the coaxial waveguide. Combined with the magnetic field (i.e., inductance) during the transmission of electromagnetic waves via the coaxial waveguide TEM, and the resistance effect introduced by the attenuating ceramic ring, a non-ideal parallel resonant circuit is formed (the corresponding equivalent circuit diagram is shown in Figure 1). Figure 2 (As shown) This is a notch filter circuit. For this non-ideal parallel resonant circuit, the expression for the quality factor Q at resonance is: , in, Where is the resonant frequency, and C is the equivalent capacitance of the circuit. Let L be the equivalent resistance of branch L.

[0014] The relationship between bandwidth BW and Q in the resonant circuit is as follows: That is, at the resonant frequency Under the condition that remains unchanged, the larger the Q value (corresponding to...) The smaller the Q value, the narrower the bandwidth; the smaller the Q value (corresponding to...) The larger the value, the wider the bandwidth. This indicates that different operating bandwidths of the oscillation circuit can be achieved by selecting different loss tangents. If the transmitted signal falls within the designed circuit bandwidth, the effect of a notch filter can be achieved.

[0015] In this embodiment, the designed notch filter should have an operating bandwidth of 4900 ± 40 MHz. A ceramic ring with appropriate dielectric constant and loss tangent is selected and designed to meet the attenuation requirements for second harmonic power within a certain bandwidth range. Figure 3 This is an external view of the notch filter.

[0016] like Figure 4 The notch filter shown consists of an outer conductor 10 with notch grooves, an inner conductor 20, and an attenuation ceramic ring 30, including two independent notch circuits.

[0017] The inner conductor 20 is the high-voltage lead of one end electrode of the magnetron cathode.

[0018] The outer conductor 10 is the high-voltage lead of the other electrode of the magnetron cathode, and it is cylindrical and concentric with the inner conductor 20.

[0019] like Figure 5 As shown, two sets of symmetrical notch slots are etched on the surface of the outer conductor. These notch slots are primarily used for impedance matching. The specific structure of one set of notch slots is as follows: A first slot 45 with a width of s is cut in half on the outer conductor 10. The first slot 45 is parallel to the plane passing through the central axis. Then, symmetrical slots with a width of g are made on both sides of the first slot 45, forming four trapezoidal slots with a height of hg (i.e., the first trapezoidal slot 41, the second trapezoidal slot 42, the third trapezoidal slot 43, and the fourth trapezoidal slot 44). The distance L between the first trapezoidal slot 41 and the fourth trapezoidal slot 44 is the same as the side length of the attenuation ceramic ring. The included angle between the first trapezoidal slot 41 and the second trapezoidal slot 42 is θ≥0°. On the other side of the outer conductor 10, another set of notch slots is etched using the same method. It should be ensured that the dimensions of each trapezoidal slot belonging to the same set are identical. The dimensions of each trapezoidal slot are determined based on simulation results.

[0020] like Figure 6 As shown, the attenuation ceramic ring 30 is a cylindrical ceramic ring. Its central hole matches the inner conductor 20, and its outer diameter matches the outer conductor 10. The two end faces of the attenuation ceramic ring are parallel and form an angle with the central axis. >0°, the two ends of the central hole of the attenuating ceramic ring are chamfered. The high dielectric constant of this attenuating ceramic ring can concentrate the electric field around it more, forming a stronger capacitance effect; on the other hand, since the attenuating ceramic ring has a large loss tangent, the bandwidth of the oscillation circuit can be changed by adjusting the loss tangent, thereby realizing the bandwidth and attenuation depth of the customized notch filter circuit.

[0021] In this embodiment, the notch filter is obtained as follows: Define the operating frequency range of the target harmonic and determine the operating bandwidth of the harmonic circuit.

[0022] Select a ceramic ring with appropriate dielectric constant, loss tangent and thermal conductivity.

[0023] Modeling was performed using CST Microwave Studio, employing discrete port excitation. The target values ​​of S11 and S21 were input into the software for parameter scanning optimization. Specifically, when all other ports are connected to a matched load, S11 = reflected wave from port 1 / incident wave from port 1, and S21 = transmitted wave from port 2 / incident wave from port 1. Ports 1 and 2 are as follows... Figure 4 As shown. The equivalent capacitance C is changed by altering the shape of the notch groove, and the equivalent resistance is changed by altering the dielectric constant of the attenuation ceramic ring. To achieve the resonant frequency of a custom notch filter circuit ; Alternatively, the equivalent resistance can be changed by altering the loss tangent of the attenuating ceramic ring. This allows for the customization of bandwidth and attenuation depth for notch filters.

[0024] Figure 7 The display shows that S11 of the notch filter circuit is less than 11 dB, indicating that the notch filter circuit and the magnetron are well matched. Figure 8 The notch filter circuit shows that S21 < 10 dB, indicating that the notch filter circuit has a significant suppressive effect on the second harmonic of the magnetron leakage.

[0025] Figure 9 With a notch filter, the S21 value of the fundamental frequency 2450 ± 20 MHz is less than -43 dB; Figure 10 Without a notch filter, the S21 value at a fundamental frequency of 2450 ± 20 MHz is less than -36 dB; Figure 9 , Figure 10 It can be seen that the notch filter circuit also has a certain suppression effect on the fundamental power leakage of the magnetron.

Claims

1. A notch filter device for suppressing microwave leakage from a magnetron, characterized in that, It includes an inner conductor (20), an attenuation ceramic ring (30) and an outer conductor (10) arranged sequentially from the inside to the outside, with a notch groove provided on the outer conductor (10); The inner conductor (20) is the high-voltage lead of one end electrode of the magnetron cathode; The outer conductor (10) is the high-voltage lead of the other end electrode of the magnetron cathode, and the central axis of the outer conductor (10) coincides with the central axis of the inner conductor (10); The central axis of the attenuation ceramic ring (30) coincides with the central axis of the inner conductor (20), the outer diameter is the same as the inner diameter of the outer conductor (10), and the inner diameter is the same as the outer diameter of the inner conductor (20). The notch groove can realize the equivalent capacitance, and the attenuation ceramic ring (30) placed between the inner conductor (20) and the outer conductor (10) can realize the equivalent resistance. Under the effect of equivalent inductance and equivalent capacitance, the magnetic field in the axial transmission process of the TEM electromagnetic wave forms an inductance effect, forming a non-ideal parallel resonant circuit. When the frequency of the transmitted signal is the same as the resonant frequency of the resonant circuit, a notch circuit is formed.

2. The notch filter device for suppressing microwave leakage of a magnetron according to claim 1, characterized in that, The surface of the outer conductor (10) is provided with two symmetrically arranged notch grooves, the notch grooves including a first groove (45) and four trapezoidal grooves; the first groove (45) is a rectangular groove parallel to the central axis, and a first trapezoidal groove (41) and a fourth trapezoidal groove (44) are arranged in a mirror image on one side of the first groove (45), and a second trapezoidal groove (42) and a third trapezoidal groove (43) are arranged in a mirror image on the other side of the first groove (45); the first trapezoidal groove (41) and the second trapezoidal groove (42) are arranged symmetrically on both sides of the first groove (45), and the third trapezoidal groove (43) and the fourth trapezoidal groove (44) are arranged symmetrically on both sides of the first groove (45); the included angle between the first trapezoidal groove (41) and the second trapezoidal groove (42) is θ≥0°.

3. The notch filter device for suppressing microwave leakage of a magnetron according to claim 2, characterized in that, The distance between the first trapezoidal groove (41) and the fourth trapezoidal groove (44) is the same as the side length of the attenuation ceramic ring (30).

4. The notch filter device for suppressing microwave leakage of a magnetron according to claim 1, characterized in that, The attenuation ceramic ring (30) is cylindrical ceramic, and the two end faces of the attenuation ceramic ring (30) are parallel, with the angle between the end faces and the central axis being . >0°, the two ends of the central hole of the attenuation ceramic ring are chamfered.

5. The notch filter device for suppressing microwave leakage of a magnetron according to any one of claims 1-4, characterized in that, The resonant frequency of a customized notch filter circuit can be achieved by changing the shape of the notch groove to alter the equivalent capacitance, or by changing the dielectric constant of the attenuating ceramic ring to alter the equivalent resistance. Alternatively, the bandwidth and attenuation depth of a customized notch filter circuit can be achieved by changing the loss tangent of the attenuation ceramic ring.

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