Slow wave structure and terahertz traveling wave tube frequency doubling amplifier

Abstract

The invention provides a slow wave structure and a terahertz traveling wave tube frequency doubling amplifier. According to the invention, the slow-wave structure designed in a segmented manner is adopted, and independent modulation and amplification of the fundamental frequency signal and the harmonic signal are combined, so that the problem of non-uniform energy distribution of electron beams in a traditional traveling wave tube is effectively solved. The first sub-slow-wave structure carries out shallow modulation on a fundamental frequency signal, excessive consumption of electron beam energy is avoided, meanwhile, a harmonic amplification section in the second sub-slow-wave structure can effectively amplify a harmonic drive signal, and the output power of higher harmonics is ensured. The electron beam gradually-changing drift channel is designed through gradually-changing diameters, energy transfer of fundamental frequency and harmonic wave sections is smoothly transited, the system efficiency, bandwidth and stability are further improved, and meanwhile nonlinear noise and oscillation risks are reduced.

Description

Technical Field

[0001] This invention relates to the technical field of vacuum electronic devices, specifically to a slow-wave structure and a terahertz traveling-wave tube frequency multiplier amplifier. Background Technology

[0002] In the field of modern terahertz technology, terahertz traveling wave tube amplifiers (TWTs) are widely used for the amplification and processing of high-frequency signals, especially in important fields such as communication, imaging, and scientific exploration in the terahertz band. Terahertz traveling wave tube amplifiers amplify input signals through the interaction between an electron beam and a slow-wave structure, effectively increasing signal power and expanding bandwidth.

[0003] Existing terahertz traveling wave tube amplifiers suffer from insufficient high-order harmonic output power due to the integrated design of the slow wave structure, which leads to excessive modulation and consumption of electron beam energy in the fundamental frequency band and the lack of an independent deep extraction mechanism in the harmonic band. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a slow-wave structure and a terahertz traveling-wave tube frequency multiplier amplifier to solve the technical problems in the related technologies, where the existing terahertz traveling-wave tube amplifiers, due to the integrated design of the slow-wave structure, cause the electron beam energy to be over-modulated and consumed in the fundamental frequency band, and the harmonic band lacks an independent deep extraction mechanism, resulting in insufficient high-order harmonic output power.

[0005] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a slow-wave structure, comprising: The first sub-slow wave structure has its input configured to receive a baseband input signal and perform shallow modulation on the baseband input signal; The second sub-slow wave structure is connected in series with the first sub-slow wave structure. The second sub-slow wave structure includes at least a harmonic amplification section. The input end of the harmonic amplification section is configured to receive a harmonic driving signal for amplifying the harmonic driving signal, and its operating frequency band is an integer multiple of the fundamental frequency input signal. An electron beam gradient drift channel connects the first sub-slow wave structure and the second sub-slow wave structure, and the channel diameter gradually changes from the size of the first sub-slow wave structure to the size of the second sub-slow wave structure.

[0006] Furthermore, the first sub-slow wave structure includes M periodic sinusoidal waveguide units connected in series, where M is a positive integer greater than 10.

[0007] Furthermore, the harmonic amplification section includes L periodic sinusoidal waveguide units connected in series, where L is a positive integer greater than M.

[0008] Furthermore, the second sub-slow wave structure also includes: A harmonic filtering section is disposed between the electron beam gradient drift channel and the harmonic amplification section; the harmonic filtering section includes N periodic sinusoidal waveguide units connected in series to suppress nonlinear noise, where N is a positive integer less than L.

[0009] Furthermore, the second sub-slow wave structure also includes: A cylindrical isolation channel is disposed between the harmonic filtering section and the harmonic amplification section to block the electromagnetic feedback path.

[0010] Furthermore, the normalized phase velocity curve of the first sub-slow wave structure coincides with the normalized phase velocity curve of the harmonic amplification section in the target operating frequency band.

[0011] Furthermore, the electron beam gradient drift channel has a conical frustum structure.

[0012] Furthermore, both the input and output ends of the first sub-slow wave structure are equipped with a first gradient structure, wherein the first gradient structure at the input end is used to match the impedance of the fundamental frequency input signal, and the first gradient structure at the output end is used to match the impedance of the shallowly modulated fundamental frequency output signal to the electron beam gradient drift channel; both the input and output ends of the second sub-slow wave structure are equipped with a second gradient structure, wherein the second gradient structure at the input end is used to match the impedance of the harmonic drive signal, and the second gradient structure at the output end is used to match the impedance of the harmonic output signal to the load.

[0013] Furthermore, both the first and second gradient structures are sinusoidal waveguide wall gradient structures, with their waveguide cross-sections continuously changing along the electron beam propagation direction and the waveguide wall curvature radius gradually changing with the transmission direction.

[0014] Secondly, the present invention provides a terahertz traveling wave tube frequency multiplier amplifier, including the slow wave structure described above.

[0015] Beneficial effects: This invention effectively solves the problem of uneven electron beam energy distribution in traditional traveling wave tubes by employing a segmented slow-wave structure and combining independent modulation and amplification of the fundamental frequency and harmonic signals. The first sub-slow-wave structure performs shallow modulation of the fundamental frequency signal, avoiding excessive consumption of electron beam energy. Simultaneously, the harmonic amplification section in the second sub-slow-wave structure effectively amplifies the harmonic drive signal, ensuring the output power of higher harmonics. The electron beam gradient drift channel, through a gradient diameter design, smoothly transitions the energy transfer between the fundamental frequency and harmonic bands, further improving system efficiency, bandwidth, and stability, while reducing nonlinear noise and oscillation risks. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the slow-wave structure of the segmented sinusoidal waveguide terahertz traveling wave tube frequency multiplier amplifier provided in an embodiment of the present invention; wherein, the first sub-slow-wave structure is composed of M single-cycle sinusoidal waveguide unit structures connected together, the second sub-slow-wave structure has a harmonic filtering section in the front, which plays a filtering role, including N cycles of sinusoidal waveguide units connected in series, and a harmonic amplification section in the back, which includes L cycles of sinusoidal waveguide units connected in series, which plays a frequency multiplier amplification role, wherein N < L, component 10 is a sinusoidal waveguide unit applicable to the first sub-slow-wave structure, component 11 is the corresponding first gradient structure, component 20 is a sinusoidal waveguide unit applicable to the second sub-slow-wave structure, and component 21 is the corresponding second gradient structure; Figure 2 This is a schematic diagram of the sinusoidal waveguide unit in the first sub-slow wave structure used in an embodiment of the present invention; Figure 3 This is a schematic diagram of the sinusoidal waveguide unit in the second sub-slow wave structure used in an embodiment of the present invention; Figure 4 This is a schematic diagram of the first and second gradient structures used in embodiments of the present invention; Figure 5 This is a schematic diagram of the electron beam gradient drift channel used in an embodiment of the present invention; Figure 6 This is a schematic diagram of the cylindrical isolation channel used in an embodiment of the present invention; Figure 7 This is a schematic diagram of the dispersion curve of the first sub-slow wave structure provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the dispersion curve of the third harmonic slow wave structure provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of the high-order harmonic output signal, the fundamental frequency output signal, and the fundamental frequency drive signal provided in the embodiments of the present invention; Figure 10 This is a schematic diagram of the gain and bandwidth provided in an embodiment of the present invention. Detailed Implementation

[0017] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0018] In the field of modern terahertz technology, terahertz traveling wave tube amplifiers (TWTs) are widely used for the amplification and processing of high-frequency signals, particularly in important areas such as communication, imaging, and scientific exploration in the terahertz band. TWTs amplify input signals through the interaction between an electron beam and a slow-wave structure, effectively increasing signal power and expanding bandwidth. However, despite these advantages, existing terahertz TWTs still face some technical bottlenecks in the effective amplification of high-order harmonic signals.

[0019] In related technologies, terahertz traveling wave tube amplifiers employ an integrated slow-wave structure, commonly using a folded waveguide design. The basic principle of this design is to support the modulation and amplification of both the fundamental frequency signal and higher harmonic signals through a unified slow waveguide. However, in practical applications, this integrated design leads to uneven energy distribution. Specifically, the excessive modulation depth of the electron beam in the fundamental frequency band results in most of the energy being excessively consumed by the fundamental frequency signal. Due to the lack of independent and deep modulation design in the higher harmonic bands, the remaining energy of the electron beam cannot be effectively utilized, resulting in the output power of the higher harmonic signals being far lower than expected.

[0020] The direct consequence of this design flaw is that although the input fundamental frequency signal is initially amplified by the traveling wave tube, the final output high-order harmonic signals are severely insufficient. Furthermore, the excessive concentration of energy on the fundamental frequency signal also amplifies nonlinear noise, further increasing the risk of system oscillation. This phenomenon severely affects the performance and stability of terahertz traveling wave tube amplifiers at high frequencies, especially in applications requiring high power and high bandwidth, limiting the widespread adoption and application of this technology.

[0021] One possible implementation provides a terahertz cascaded traveling wave tube (TWT) frequency multiplier structure. This implementation retains the overall structure of a traditional TWT, including an electron gun assembly, a slow-wave structure, a cathode, and an anode. These structures ensure the TWT can operate normally, amplifying signals in a vacuum environment through the interaction between the electron beam and the slow-wave structure. In this implementation, multiple harmonic systems are cascaded between the TWT output slow-wave structure and the collector. These harmonic systems optimize nonlinear interactions in high-frequency systems, extracting, amplifying, and outputting harmonic information. Each cascaded harmonic system includes a slow-wave structure, a concentrated attenuator, and a harmonic output coupling structure, utilizing multiple harmonic interactions to enhance signal power.

[0022] Understandably, in this implementation scheme, although the cascaded harmonic system can amplify harmonic signals, there is an uneven energy distribution problem because the fundamental and harmonic bands rely on the same electron beam channel and focusing system. The energy of the electron beam is mainly concentrated on the modulation of the fundamental frequency signal, resulting in limited output of higher harmonic signals, failing to achieve the expected high power output. Due to the lack of an effective electron beam energy optimization mechanism, the extraction and amplification of higher harmonics are limited, especially in the higher harmonic frequency band, where insufficient power remains a problem.

[0023] In this implementation, a centralized attenuator is used to avoid self-oscillation, but this implementation still cannot completely eliminate the impact of nonlinear noise on system performance. In the cascading process of multiple harmonic systems, nonlinear noise may not be sufficiently suppressed in some cases, and will still affect the quality of the output signal, especially at higher power levels, where the risks of oscillation and noise amplification are more significant.

[0024] Therefore, in existing technologies, terahertz traveling wave tube amplifiers, due to their over-reliance on integrated slow-wave structures, suffer from imbalanced electron beam energy distribution and insufficient amplification of higher harmonic signals. How to ensure effective amplification of higher harmonic signals while avoiding energy waste and system instability caused by over-modulation of the fundamental frequency signal has become a key technical problem in this field.

[0025] The core inventive concept of this application is to provide a new solution to the problems of existing technologies through a segmented sinusoidal waveguide slow-wave structure. By optimizing the structural design of the fundamental frequency band and the higher harmonic bands, the energy of the electron beam is rationally distributed, and the residual energy of the electron beam is deeply extracted through an independent harmonic amplification section. This effectively improves the output power of the higher harmonics and significantly reduces nonlinear noise and oscillation risk, ultimately enhancing the performance and stability of the terahertz traveling wave tube amplifier in the high-frequency band.

[0026] like Figure 1 As shown, this embodiment provides a slow-wave structure, including: The first sub-slow wave structure has its input configured to receive a baseband input signal and perform shallow modulation on the baseband input signal.

[0027] like Figure 2 As shown, in this embodiment, the first sub-slow wave structure can be a fundamental frequency slow wave structure, which can include M periodic sinusoidal waveguide units connected in series, where M is a positive integer greater than 10.

[0028] Specifically, the first sub-slow wave structure is used to receive the fundamental frequency input signal and lightly modulate the electron beam to limit the fundamental frequency energy conversion rate. The purpose is to prevent excessive saturation of the electron beam in the fundamental frequency band, reserving sufficient energy for subsequent harmonic amplification.

[0029] The first sub-slow wave structure can be composed of M periodic sinusoidal waveguide units connected in series along the electron beam propagation direction. The sinusoidal waveguide units in the first sub-slow wave structure can have the following structure: Figure 1 As shown in component 10. Component 11 may also be provided in front of component 10, and component 11 may be a first gradient structure.

[0030] Understandably, each sinusoidal waveguide unit is a fundamental building block of the fundamental frequency slow-wave structure. The shape of this sinusoidal waveguide unit can be a sinusoidal waveguide, a design that effectively controls the trajectory of the electron beam and its coupling with the signal. The period length of the sinusoidal waveguide unit can be matched to the wavelength of the fundamental frequency input signal to ensure efficient interaction between the signal and the electron beam.

[0031] Understandably, M sinusoidal waveguide units with consecutive cycles are connected in series to form a complete fundamental frequency slow wave structure. M is a positive integer greater than 10, representing the number of waveguide units. The specific value of M can be based on the control of the modulation depth of the electron beam and the bandwidth requirements of the system. It is also understandable that a larger number of cycles helps to provide sufficient interaction time, ensuring that the fundamental frequency input signal can be effectively modulated with the electron beam.

[0032] Understandably, the purpose of shallow modulation is to avoid excessive energy consumption of the fundamental frequency input signal while not interfering with the formation and amplification of higher harmonic signals. Through this modulation method, the system can maintain signal strength while ensuring that more electron beam energy is transferred to subsequent harmonic bands.

[0033] In this embodiment, the dimensions of each sinusoidal waveguide unit (e.g., the width, height, and diameter of the waveguide channel) can be designed based on the frequency of the fundamental input signal, the characteristics of the electron beam, and the required modulation depth. In other words, in this embodiment, the specific dimensions of each sinusoidal waveguide unit are not limited.

[0034] like Figure 2 As shown, in one specific implementation, the sinusoidal waveguide unit can have a V-shaped cross-section design, gradually narrowing downwards to form a rounded bottom. This shape design helps to enhance the electromagnetic field distribution within the waveguide and optimize the coupling effect between the electron beam and the electromagnetic wave.

[0035] In one specific implementation, the shape of the sinusoidal waveguide unit can vary according to a sine curve, forming periodic peaks and troughs, resulting in a periodically undulating structure. This structure helps maintain good propagation characteristics across different frequency bands. Understandably, the sinusoidal waveform design provides excellent dispersion characteristics for the propagation of fundamental and higher harmonic signals, enabling effective coupling between the electron beam and the signal.

[0036] In one specific implementation, a cylindrical electron beam channel can be positioned at the center of the sinusoidal waveguide unit. This channel runs through the entire center of the sinusoidal waveguide unit, providing passage space for the electron beam. The diameter of the electron beam channel can be larger than the envelope diameter of the electron beam to ensure that the electron beam passes smoothly through the channel and to minimize the interaction between the electron beam and the signal, thereby avoiding excessive scattering or energy loss.

[0037] In one specific implementation, the channel walls may be made of an all-metal conductor (e.g., oxygen-free copper).

[0038] In one specific implementation, the waveguide wall profile of a sinusoidal waveguide element can be described by a standard sine function.

[0039] In this embodiment, the shallow modulation can be described as the interaction strength or depth between the electron beam and the fundamental frequency input signal being limited within a controllable range. This ensures that the energy of the electron beam is not excessively consumed in the modulation of the fundamental frequency input signal, but rather that sufficient energy is maintained for the modulation and amplification of subsequent harmonic signals. That is, during modulation, only a portion of the electron beam's energy is absorbed by the fundamental frequency input signal, avoiding excessive energy concentration at the fundamental frequency, and instead maintaining sufficient energy to be transferred to subsequent harmonic bands for effective amplification of higher-order harmonic signals.

[0040] In this embodiment, the interaction depth between the electron beam and the signal can be controlled by limiting the electric field strength. In this embodiment, the electric field strength is limited to a preset range (which can be determined experimentally). This preset range is sufficient to moderately modulate the fundamental frequency input signal without causing excessive energy consumption of the electron beam. By controlling the electric field strength, the interaction strength between the electron beam and the fundamental frequency signal can be precisely adjusted, thereby achieving shallow modulation.

[0041] In this embodiment, shallow modulation can be achieved by designing the dimensions of the sinusoidal waveguide unit. It is understood that the periodic waveform and dimensions of the sinusoidal waveguide unit control the propagation characteristics of the fundamental frequency input signal within the channel. Waveguide design ensures that the interaction between the signal and the electron beam is limited to the shallow modulation range. For example, the waveguide wall amplitude of the sinusoidal waveguide unit can be set to a preset value (which can be determined through prior experiments). This ensures that the interaction intensity between the electron beam and the fundamental frequency signal during modulation is moderate, thereby avoiding excessive energy consumption.

[0042] In a specific implementation, the electron beam channel diameter, waveguide wall amplitude, period length, and total number of periods can all be designed to achieve shallow modulation.

[0043] The second sub-slow wave structure is connected in series with the first sub-slow wave structure. The second sub-slow wave structure includes at least a harmonic amplification section. The input end of the harmonic amplification section is configured to receive a harmonic driving signal for amplifying the harmonic driving signal, and its operating frequency band is an integer multiple of the fundamental frequency input signal.

[0044] like Figure 3 As shown, in this embodiment, the harmonic amplification section includes L sinusoidal waveguide units connected in series with each other, where L is a positive integer greater than M.

[0045] In this embodiment, the sinusoidal waveguide unit of the harmonic amplification section can be structured as follows: Figure 1 The component 20 shown can be preceded by a component 21, which can be represented as a second gradient structure.

[0046] In this embodiment, the second sub-slow wave structure further includes a harmonic filtering section disposed between the electron beam gradient drift channel and the harmonic amplification section; the harmonic filtering section includes N periodic sinusoidal waveguide units connected in series in sequence, used to suppress nonlinear noise, where N is a positive integer less than L.

[0047] In this embodiment, the sinusoidal waveguide unit of the harmonic filtering section can be structured as follows: Figure 1 The component 20 shown can be preceded by a component 21, which can be represented as a second gradient structure.

[0048] In this embodiment, the second sub-slow wave structure is mainly responsible for receiving the output signal from the first sub-slow wave structure and amplifying the harmonic drive signal. This structure includes multiple sub-modules, specifically a harmonic amplification section and a harmonic filtering section. These two sub-modules are used to amplify higher-order harmonic signals while suppressing unwanted noise.

[0049] Specifically, the main function of the harmonic amplification section is to receive the input harmonic drive signal and amplify it. This part can include multiple sinusoidal waveguide units connected in series, each of which is responsible for effectively interacting with the electron beam to ensure that the signal amplification process is stable and uniform, and does not cause energy waste.

[0050] In the harmonic amplification section, the shape of each sinusoidal waveguide unit can be similar to that of the sinusoidal waveguide unit in the first sub-slow wave structure, both being sinusoidal. The waveguide unit exhibits periodic sinusoidal undulations along the electron beam propagation direction to ensure effective coupling between the electron beam and the signal. The harmonic amplification section includes L sinusoidal waveguide units connected in series, where L is a positive integer greater than M, indicating that the number of periods in this section is greater than the number of periods in the first sub-slow wave structure. Increasing the number of periods increases the interaction time between the electron beam and the signal, thereby improving amplification efficiency and stability.

[0051] In this embodiment, the operating frequency band of the harmonic amplification section is an integer multiple of the fundamental frequency input signal, that is, its frequency is a multiple of the fundamental frequency signal frequency. For example, if the fundamental frequency signal is 224 GHz, the operating frequency band of the harmonic amplification section can be twice the fundamental frequency or higher, in order to enhance the signal power of higher harmonics.

[0052] In this embodiment, in the second sub-slow wave structure, the harmonic filtering section is located between the electron beam gradient drift channel and the harmonic amplification section. The function of the harmonic filtering section is to filter out the nonlinear noise generated during the interaction between the electron beam and the fundamental frequency signal, ensuring that the final output signal is pure and reducing interference to the system.

[0053] In this embodiment, the harmonic filtering section can also be composed of multiple sinusoidal waveguide units, each of which can also exhibit a periodic sinusoidal waveform. Unlike the harmonic amplification section, the purpose of the harmonic filtering section is to effectively suppress unwanted frequency components (i.e., nonlinear noise) through the structural characteristics of the waveguide.

[0054] Understandably, the harmonic filtering section comprises N sinusoidal waveguide units connected in series, where N is a positive integer less than L, indicating that this section has fewer cycles than the harmonic amplification section. Fewer cycles facilitate faster signal filtering and reduce unnecessary delays and signal loss.

[0055] An electron beam gradient drift channel connects the first sub-slow wave structure and the second sub-slow wave structure, and the channel diameter gradually changes from the size of the first sub-slow wave structure to the size of the second sub-slow wave structure.

[0056] In this embodiment, the electron beam gradient drift channel can be frustum-shaped, meaning the channel diameter gradually narrows from one end to the other. This design facilitates a smooth transition, ensuring that the electron beam does not undergo abrupt changes or scattering during its propagation from the first sub-slow wave structure to the second sub-slow wave structure. In other words, the size change of the electron beam gradient drift channel is gradual, transitioning from a larger diameter to a smaller diameter. This gradual design helps reduce energy loss due to size mismatch while maintaining the stability of the electron beam.

[0057] Understandably, the gradient shape ensures that the electron beam does not undergo drastic changes within the gradually decreasing channel, maintaining its stability and focus. Secondly, the gradient design avoids scattering and energy loss during sudden contraction or expansion of the electron beam. In this way, the electron beam's energy is efficiently transferred without excessive energy loss or scattering due to mismatched channel dimensions.

[0058] In one specific implementation, the electron beam gradient drift channel can be a conical frustum structure, formed by splicing two coaxial cylinders. The diameter of the channel gradually decreases in the direction of electron beam propagation, exhibiting a smooth gradient transition. The inlet diameter of the electron beam gradient drift channel can be matched with the output size of the first sub-slow wave structure, and the outlet diameter of the electron beam gradient drift channel can be matched with the input size of the second sub-slow wave structure.

[0059] This embodiment effectively solves the problem of uneven electron beam energy distribution in traditional traveling wave tubes by employing a segmented slow-wave structure and combining independent modulation and amplification of the fundamental frequency and harmonic signals. The first sub-slow-wave structure performs shallow modulation of the fundamental frequency signal, avoiding excessive consumption of electron beam energy. At the same time, the harmonic amplification section in the second sub-slow-wave structure effectively amplifies the harmonic drive signal, ensuring the output power of higher harmonics. The electron beam gradient drift channel, through a gradient diameter design, smoothly transitions the energy transfer between the fundamental frequency and harmonic bands, further improving system efficiency, bandwidth, and stability, while reducing nonlinear noise and oscillation risks.

[0060] In some embodiments, the first sub-slow wave structure includes M periodic sinusoidal waveguide units connected in series, where M is a positive integer greater than 10.

[0061] In this embodiment, the first sub-slow wave structure, through M periodic sinusoidal waveguide units connected in series, sufficiently prolongs the interaction between the fundamental frequency input signal and the electron beam, thereby effectively improving the modulation efficiency of the fundamental frequency input signal. By setting a period number greater than 10, not only is the interaction time between the electron beam and the signal increased, but the uniformity and stability of signal modulation are also ensured. This facilitates shallow modulation, avoids excessive consumption of the fundamental frequency input signal, and provides sufficient energy support for the effective extraction of subsequent higher harmonic signals, thereby improving the overall power output and efficiency of the system.

[0062] In some embodiments, the harmonic amplification section includes L sinusoidal waveguide units connected in series with each other, where L is a positive integer greater than M.

[0063] In this embodiment, the harmonic amplification section uses L sinusoidal waveguide units connected in series to sufficiently prolong the interaction between the electron beam and the harmonic signal, thereby effectively amplifying the higher harmonic signals. Since L > M, meaning the number of periods in the harmonic amplification section is greater than the number of periods in the first sub-slow wave structure, this design provides a longer modulation path, enhances the energy exchange efficiency between the electron beam and the harmonic signal, and significantly improves the output power of the higher harmonics. Simultaneously, the increased number of periods helps to further optimize the signal gain, ensuring that the harmonic signal can be stably output at higher power, thereby improving the system's performance and stability in the high-frequency band.

[0064] In some embodiments, the second sub-slow wave structure further includes: A harmonic filtering section is disposed between the electron beam gradient drift channel and the harmonic amplification section; the harmonic filtering section includes N periodic sinusoidal waveguide units connected in series to suppress nonlinear noise, where N is a positive integer less than L.

[0065] In this embodiment, the harmonic filtering section, positioned between the electron beam gradient drift channel and the harmonic amplification section, effectively suppresses noise caused by nonlinear modulation using N-cycle sinusoidal waveguide units. This design helps filter out unwanted frequency components, ensuring signal purity. Since N < L, meaning the harmonic filtering section has fewer cycles than the harmonic amplification section, effective noise filtering can be achieved within a shorter path, avoiding unnecessary signal loss and delay. This design ensures effective amplification of higher-order harmonic signals during transmission while reducing the impact of noise on system performance, thereby improving the quality and stability of the system output signal.

[0066] like Figure 6 As shown, in some embodiments, the second sub-slow wave structure further includes: A cylindrical isolation channel is disposed between the harmonic filtering section and the harmonic amplification section to block the electromagnetic feedback path.

[0067] In this embodiment, the diameter of the cylindrical isolation channel can be the same as the size of the electron beam channel in the slow-wave structure, and its length is related to the modulation phase of the electron beam, isolating the electromagnetic wave signals before and after, and playing the role of filtering and eliminating self-excitation.

[0068] In this embodiment, the cylindrical isolation channel, designed with the same dimensions as the electron beam channel in the slow-wave structure, ensures that the electron beam is not interfered with during transmission, while effectively isolating electromagnetic wave signals from the preceding and following segments. This design optimizes the modulation phase of the electron beam, avoiding signal distortion caused by electromagnetic feedback. The length of the cylindrical isolation channel is related to the modulation phase of the electron beam, ensuring the system's efficient filtering function, effectively suppressing unwanted electromagnetic signals, and preventing self-oscillation. This design significantly improves system stability, reduces noise interference, and ensures the purity and amplification effect of harmonic signals, thereby improving the overall system performance and signal quality.

[0069] In some embodiments, the normalized phase velocity curve of the first sub-slow wave structure coincides with the normalized phase velocity curve of the harmonic amplification section in the target operating frequency band.

[0070] In this embodiment, the target operating frequency band refers to the frequency band in which the normalized phase velocity curves of the first sub-slow wave structure (fundamental frequency band) and the harmonic amplification segment coincide. That is, within this frequency band, the speed of the electron beam and the propagation speed of the electromagnetic wave are consistent, ensuring that the electron beam can maintain synchronous modulation with the signal, thereby effectively transferring energy.

[0071] In this embodiment, the normalized phase velocity refers to the ratio of the phase velocity (i.e., the speed at which electromagnetic waves propagate in a waveguide) to the speed of light. The coincidence of the two phase velocity curves indicates that the fundamental frequency input signal and the higher harmonic signals have the same synchronicity during operation, making the signal modulation and amplification process more efficient.

[0072] Understandably, to achieve synchronous operation, the normalized phase velocity curve of the first sub-slow wave structure coincides with the normalized phase velocity curve of the harmonic amplification section within the target operating frequency band. Under this matching condition, the switching process of the electron beam between the fundamental frequency input signal and the harmonic input signal will not cause energy loss or signal distortion.

[0073] In this embodiment, the normalized phase velocity curve of the first sub-slow wave structure coincides with the normalized phase velocity curve of the harmonic amplification section in the target operating frequency band, ensuring good synchronization between the electron beam and the signal throughout the entire frequency band. This design optimizes energy transfer between the electron beam and the fundamental frequency signal and harmonic signals, enabling the signal to be modulated and amplified efficiently. Due to phase velocity matching, the electron beam will not experience phase decoupling with the signal, thereby effectively avoiding energy loss, signal distortion, and nonlinear noise, improving the overall power output, bandwidth, and signal quality of the system, and ensuring the stability and high efficiency of the system in the target frequency band.

[0074] like Figure 5 As shown, in some embodiments, the electron beam gradient drift channel is a truncated cone structure.

[0075] In this embodiment, the electron beam gradient drift channel adopts a conical frustum structure. Through a smooth, gradual dimensional change, the transmission path and beam stability of the electron beam are effectively controlled. The conical structure causes the electron beam to gradually narrow within the channel, avoiding uneven scattering or energy loss during its passage and ensuring efficient modulation and amplification of the electron beam in the subsequent slow-wave structure. This design also reduces the contact area between the electron beam and the channel wall, further reducing the electron beam interception rate and improving the system's energy transfer efficiency and overall stability.

[0076] like Figure 4 As shown, in some embodiments, both the input and output ends of the first sub-slow wave structure are configured with a first gradient structure, wherein the first gradient structure at the input end is used to match the impedance of the fundamental frequency input signal, and the first gradient structure at the output end is used to match the impedance of the shallowly modulated fundamental frequency output signal to the electron beam gradient drift channel; both the input and output ends of the second sub-slow wave structure are configured with a second gradient structure, wherein the second gradient structure at the input end is used to match the impedance of the harmonic drive signal, and the second gradient structure at the output end is used to match the impedance of the harmonic output signal to the load.

[0077] In this embodiment, the first gradient structure can be as follows: Figure 1 As shown in component 11, the second gradient structure can be as follows: Figure 1 Component 21 is shown in the figure.

[0078] In this embodiment, both the input and output ends of the first and second sub-slow wave structures are equipped with gradient structures. Through the precise design of these gradient structures, the impedance between the signal and the channel is effectively matched. The first gradient structure at the input end optimizes the impedance matching of the fundamental frequency input signal, ensuring effective signal transmission to the first sub-slow wave structure and reducing reflection loss. The first gradient structure at the output end optimizes the impedance matching between the shallowly modulated fundamental frequency output signal and the electron beam gradient drift channel, ensuring a smooth signal transition and maximizing energy transmission efficiency. For the second sub-slow wave structure, the second gradient structure at the input end matches the impedance of the harmonic drive signal, ensuring effective signal amplification. The second gradient structure at the output end matches the impedance of the harmonic output signal with the load, ensuring efficient signal output and reducing reflection loss. Through these impedance matching gradient structures, the overall transmission efficiency of the system is significantly improved, signal quality is optimized, and energy loss, distortion, or reflection caused by impedance mismatch is avoided, thus enhancing the system's performance and stability.

[0079] In some embodiments, the first and second gradient structures are both sinusoidal waveguide wall gradient structures, whose waveguide cross-section changes continuously along the electron beam propagation direction, and whose waveguide wall curvature radius changes gradually with the propagation direction.

[0080] In one specific implementation, a slow-wave structure for a terahertz traveling wave tube frequency multiplier amplifier based on a segmented sinusoidal waveguide is provided.

[0081] Understandably, a terahertz traveling wave tube (TWT) frequency multiplier or amplifier is a terahertz vacuum electronic device based on an innovative design of a TWT amplifier. It can amplify and increase the frequency of the preceding terahertz signal several times. Conventional TWT devices require a corresponding pre-amplifier drive signal source, but solid-state devices cannot generate sufficiently powerful drive signals at higher terahertz frequencies. The TWT frequency multiplier or amplifier, however, can, to some extent, avoid dependence on a high-frequency terahertz pre-amplifier drive signal source and produce output power several orders of magnitude higher than existing TWT amplifiers in the same frequency band.

[0082] Terahertz traveling wave tube (TWT) frequency multipliers or amplifiers have wide applications in various fields, including high-speed terahertz communication, public safety monitoring, biomedical imaging, astronomical observation, and high-precision non-destructive testing. Currently, terahertz signal sources utilize technologies such as solid-state devices, vacuum electronic devices, and free-electron lasers. However, due to various limitations, it is difficult to achieve stable output with both high bandwidth and high power at higher terahertz frequencies. While TWT amplifiers offer relatively high bandwidth, their performance at higher terahertz frequencies is limited by the performance of the preceding driver signal source. This invention proposes a segmented sinusoidal waveguide-based TWT frequency multiplier or amplifier that can obtain high-bandwidth, high-power output signals in the higher harmonic frequency band using only the fundamental frequency signal as the driver signal source.

[0083] This implementation scheme does not require full modulation of the fundamental frequency signal, but only a short number of cycles for initial modulation. This avoids the signal power being concentrated on the fundamental frequency for output due to excessive beam-wave interaction. In this state, the higher harmonic signals are not obvious, and their signal amplitude is only one-tenth or even less of the fundamental frequency. Subsequently, the electron beam is remodulated by the higher harmonic slow-wave structure to suppress the fundamental frequency signal and amplify the higher harmonic signals. At the same time, the higher harmonics are amplified a second time through the input of the higher harmonic drive signal. In addition, this implementation scheme innovatively uses a segmented sinusoidal waveguide as the slow-wave system structure, which can significantly improve the operating bandwidth. These are the key research contents of this invention.

[0084] Furthermore, a high-order harmonic periodic sinusoidal slow-wave structure (second sub-slow-wave structure) is designed. The dispersion curve of this slow-wave structure basically matches the dispersion curve of the fundamental frequency slow-wave structure (first sub-slow-wave structure), and the operating frequency is an integer multiple of the fundamental frequency, requiring strict correspondence to maintain the overall structure's operating bandwidth within a wide range. Its synchronization voltage matches the synchronization voltage of the fundamental frequency periodic sinusoidal slow-wave structure, ensuring that the electron beam has the same synchronization voltage in different slow-wave bands.

[0085] Furthermore, corresponding gradient structures are designed for the first and second sub-slow wave structures to match the impedance of the input and output signals and reduce the emission coefficient and loss coefficient.

[0086] Furthermore, the electron beam drift channel designed between the first and second sub-slow wave structures has a length related to the modulation phase of the electron beam and a shape that is a gradually decreasing frustum-shaped channel. This channel connects the larger electron beam channel in the fundamental frequency slow wave structure (first sub-slow wave structure) with the smaller electron beam channel in the higher harmonic slow wave structure (second sub-slow wave structure). This requires multiple optimizations to reduce the noise signal introduced by remodulation.

[0087] Furthermore, a high-order harmonic slow wave structure (harmonic filtering section) with several to a dozen harmonics is designed to further filter out noise signals.

[0088] Furthermore, a cylindrical isolation channel is designed to connect the two high-order harmonic slow wave structures. The channel is cylindrical in shape, with a diameter the same as that of the electron beam channel in the slow wave structure. Its length is related to the modulation phase of the electron beam, thus isolating the electromagnetic wave signals before and after the channel and playing a role in filtering and eliminating self-excitation.

[0089] In one specific implementation, a terahertz traveling-wave tube frequency multiplier amplifier is provided, capable of amplifying a 224 GHz signal to 672 GHz. The fundamental frequency sinusoidal waveguide slow-wave circuit (first sub-slow-wave structure) consists of 60 sinusoidal periodic structures, with an electron beam channel diameter of 0.15 mm, significantly smaller than the electron channel size of a typical traveling-wave tube amplifier slow-wave circuit in this frequency band. This reduces the design complexity of the electron optics system. Initial modulation of the electron beam with an envelope diameter of 0.08 mm is possible. In the shorter fundamental frequency slow-wave circuit, the electron beam is not modulated to saturation or even beyond, preventing excessive shunting of electron beam energy and significant suppression of the fundamental frequency output power. At this point, the current signal of the electron beam at the end of the fundamental frequency slow-wave circuit will contain very small harmonic signals. This example requires the third harmonic signal; therefore, after passing through the first electron beam drift channel, a third harmonic slow-wave circuit (second sub-slow-wave structure) in the 670 GHz band is needed to amplify and extract the effective signal. The 670GHz band slow wave circuit consists of a 10-cycle filtering section (harmonic filtering section) and a 100-cycle amplification section (harmonic amplification section). Through simulation calculations, the filtering section can effectively suppress noise signals caused by secondary modulation and suppress the generation of self-excited signals.

[0090] In this embodiment, an electron optics system with a voltage of 23.25kV, a current of 65mA, and an envelope diameter of 0.08mm was used to provide a high-quality electron beam. Simulation results show that when a 224GHz signal with a saturation drive power of 5mW is input, the segmented sinusoidal terahertz frequency multiplier amplifier can obtain an output power of 19.2W with a bandwidth of 15GHz (663-681GHz) at 672GHz. When a 672GHz signal with a drive power of 1mW is input simultaneously, the final output power can be increased to 20W. Figure 7 It is the dispersion curve of a single-period structure in the fundamental frequency band. Figure 8 It is the dispersion curve of a single-period structure in the third harmonic band. Figure 9 This is the final output diagram of the fundamental frequency and third harmonic signal. Figure 10 This is a gain and bandwidth diagram.

[0091] This implementation scheme's segmented sinusoidal terahertz traveling wave tube (TWT) frequency multiplier slow-wave structure improves upon the basic TWT amplifier and frequency multiplier by enhancing the slow-wave circuit structure. It increases the amplification effect of higher harmonic drive signals on higher harmonics and proposes using a shorter higher harmonic slow-wave circuit to filter noise signals and reduce self-oscillation signals. This significantly improves the power output performance of the TWT device in the higher terahertz frequency band. Simultaneously, it addresses the current experimental conditions where a high-frequency pre-stage drive signal source for terahertz TWTs is lacking.

[0092] The simulation analysis results of this implementation scheme show that the segmented sinusoidal slow wave structure in this scheme improves the bandwidth of the entire system. At the same time, the shorter fundamental frequency slow wave band results in shallower modulation of the fundamental frequency signal band and very low output power of the fundamental frequency signal, which concentrates more energy on the third harmonic, greatly improving the output power of the third harmonic signal. In addition, the design of the filter section effectively suppresses the noise signal introduced by nonlinear modulation, thereby improving the stability of the system and eliminating the risk of oscillation.

[0093] This embodiment provides a terahertz traveling wave tube frequency multiplier amplifier, including the slow wave structure described above.

[0094] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0095] Optionally, specific examples in this embodiment can refer to the examples described in the above embodiments, and will not be repeated here.

[0096] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0097] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0098] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A slow-wave structure, characterized in that, include: The first sub-slow wave structure has its input configured to receive a baseband input signal and perform shallow modulation on the baseband input signal; The second sub-slow wave structure is connected in series with the first sub-slow wave structure. The second sub-slow wave structure includes at least a harmonic amplification section. The input end of the harmonic amplification section is configured to receive a harmonic driving signal for amplifying the harmonic driving signal, and its operating frequency band is an integer multiple of the fundamental frequency input signal. An electron beam gradient drift channel connects the first sub-slow wave structure and the second sub-slow wave structure, and the channel diameter gradually changes from the size of the first sub-slow wave structure to the size of the second sub-slow wave structure.

2. The slow-wave structure according to claim 1, characterized in that, The first sub-slow wave structure comprises M periodic sinusoidal waveguide units connected in series, where M is a positive integer greater than 10.

3. The slow-wave structure according to claim 2, characterized in that, The harmonic amplification section includes L sinusoidal waveguide units connected in series with each other, where L is a positive integer greater than M.

4. The slow-wave structure according to claim 3, characterized in that, The second sub-slow wave structure also includes: A harmonic filtering section is disposed between the electron beam gradient drift channel and the harmonic amplification section; the harmonic filtering section includes N periodic sinusoidal waveguide units connected in series to suppress nonlinear noise, where N is a positive integer less than L.

5. The slow-wave structure according to claim 4, characterized in that, The second sub-slow wave structure also includes: A cylindrical isolation channel is disposed between the harmonic filtering section and the harmonic amplification section to block the electromagnetic feedback path.

6. The slow-wave structure according to any one of claims 1 to 5, characterized in that, The normalized phase velocity curve of the first sub-slow wave structure coincides with the normalized phase velocity curve of the harmonic amplification section in the target operating frequency band.

7. The slow-wave structure according to any one of claims 1 to 5, characterized in that, The electron beam gradient drift channel has a conical frustum structure.

8. The slow-wave structure according to any one of claims 1 to 5, characterized in that, The first sub-slow wave structure has a first tapered structure at both its input and output ends. The first tapered structure at the input end is used to match the impedance of the fundamental frequency input signal, and the first tapered structure at the output end is used to match the impedance of the shallowly modulated fundamental frequency output signal to the electron beam tapered drift channel. The second sub-slow wave structure has a second tapered structure at both its input and output ends. The second tapered structure at the input end is used to match the impedance of the harmonic drive signal, and the second tapered structure at the output end is used to match the impedance of the harmonic output signal to the load.

9. The slow-wave structure according to any one of claims 8, characterized in that, Both the first and second gradient structures are sinusoidal waveguide wall gradient structures, with their waveguide cross-sections continuously changing along the electron beam propagation direction and the waveguide wall curvature radius gradually changing with the transmission direction.

10. A terahertz traveling wave tube frequency multiplier amplifier, characterized in that, Includes the slow-wave structure as described in any one of claims 1 to 9.

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