Research On Key Technology Of Broadband High-Power Millimeter-Wave Multi-Mode Modulation

The gyrotron traveling-wave tube（gyro-TWT）stands out as the singular amplifier within the millimeter-wave frequency spectrum capable of achieving high average power,peak power,and wide-band output.It finds extensive application potential in domains such as deep space exploration and communication,long-range high-resolution radar,and electronic warfare.Nevertheless,the inherent output waveguide mode of gyro-TWT does not readily lend itself to direct utilization.Rather,it necessitates directional control for efficient conversion from waveguide mode to spatial mode.Thus,the research into wideband high-power millimeter-wave directional control technology emerges as a pivotal element in the application of high-power millimeter-wave technology,carrying substantial significance for the advancement of high-performance high-power millimeter-wave systems.To circumvent power breakdown and minimize transmission losses,high-power millimeter-wave source systems conventionally adopt oversize waveguide for energy transmission.Oversize waveguide exhibits a diverse mode spectrum,rendering it prone to the excitation of parasitic modes during directional mode control.On one hand,the existence of various parasitic modes complicates the task of achieving efficient beam conversion across a wide frequency band,thereby constraining the performance capabilities of high-power gyro-TWT systems.Conversely,the amalgamation of parasitic modes with operating modes precipitates a rapid escalation in local field strength,thereby heightening the risk of power breakdown.Consequently,realizing efficient and stable mode conversion in oversize waveguide within a broad frequency band presents an urgent technical challenge in contemporary high-power millimeter-wave applications.Furthermore,the individual output power of a singular gyro-TWT merely reaches the level of hundreds to thousands of kilowatts,falling short of meeting the demand for higher power in practical applications.The dissertation addresses the bandwidth limitations of mode conversion in high-power millimeter-wave transmission,the instability engendered by parasitic modes,and the constrained output of individual power sources.Bandwidth extension technology for highly oversized smooth waveguide mode conversion,elucidation of the interference mechanism and mitigation strategies for parasitic modes in smooth oversize waveguide mode conversion,and exploration of efficient broadband power combination technology grounded on hologram mirrors are undertaken.The specific endeavors undertaken are outlined as follows:1.Research on bandwidth expansion techniques for oversized smooth waveguide mode conversion.To address the challenges of efficient mode directional conversion and limited operational bandwidth in oversized waveguides,an in-depth analysis of mode coupling mechanisms within oversized smooth-walled waveguides was conducted.Combining these insights with efficient optimization strategies,methods for expanding the bandwidth of mode converters were explored.For the serpentine bend mode converter,elliptical waveguides were employed to construct perturbation structures.Based on a thorough analysis of mode coupling coefficients in elliptical waveguides,an elliptical waveguide structure was proposed that maximizes mode conversion efficiency.Building on this,an optimization method for a broadband,highly efficient serpentine bend mode converter using oversized elliptical waveguides was proposed.For the Gaussian feed,a characterization relationship between the radiation characteristics of circular horn feeds and waveguide mode composition was established.A stepwise inverse design method using the basic particle swarm optimization algorithm was proposed,achieving rapid and efficient design of electrically large waveguide feeds.Based on the proposed methods,a W-band oversized serpentine bend mode converter and a Gaussian feed were developed.Results demonstrate that the serpentine mode converter achieves over 95%mode conversion efficiency within the frequency range of 85 GHz to 103.5GHz,corresponding to a relative bandwidth of up to 19.4%,with a power capacity exceeding 1.4 MW.The Gaussian feed source outputs highly symmetrical beams within the range of 80 GHz to 110 GHz,with a relative bandwidth of 31.6%.Moreover,the in-band output gain exceeds 26.2 d B,sidelobes are lower than-22 d B,and the power capacity reaches 3.2 MW.2.Research on the interference mechanism of parasitic modes on mode conversion and their suppression methods.Focusing on serpentine mode converters and Gaussian feed sources,their performance variations across wide frequency bands are studied concerning different proportions and phase mixtures of operating modes and parasitic modes inputs.Focusing on the broadband operational characteristics of serpentine bend mode converters and Gaussian feeds,a quantitative analysis was conducted on the output performance variations across a wide frequency band when the operating mode and parasitic modes are mixed in different proportions and phases.Based on this analysis,the investigation into multiple parasitic modes revealed that the interference caused by parasitic modes on mode conversion is independent.This allows for the calculation of mode conversion results for multi-mode inputs by superimposing the interference values of each parasitic mode.To mitigate the interference of parasitic modes on mode conversion,research was conducted on waveguide mode filtering methods targeting parasitic modes.Utilizing the differences in angular surface current components between the working mode TE₀₁ and parasitic modes,non-TE₀₁ mode filtering methods based on circular waveguide angular slot arrays and quasi-circular waveguide slot coupling were proposed.These methods achieved efficient transmission of the circular waveguide TE₀₁ mode while effectively filtering out parasitic modes.Mode filters developed using this method can attenuate the transmission efficiency of TE₀₁mode to below-17.5 d B over a bandwidth exceeding 42.4%.3.Research on high-efficient and broadband spatial power combination/division technology based on hologram mirrors:Addressing the issue of limited output from individual high-power sources,this section explores methods for achieving efficient,stable,and broadband power combination in open space using the phase correction capabilities of hologram mirrors.Analyzing the minimum spacing between beams,a design method for spatial power combination/division devices based on hologram mirrors is proposed.Two spatial power divider devices designed using this method demonstrate efficiencies exceeding 95%,maintaining efficiencies above 90%within a relative bandwidth of 30%.To further enhance the operational bandwidth of hologram mirror systems,methods for implementing broadband mirrors are studied.A partition-frequency optimization method is introduced to solve the issue of inability to directly superimpose optimization values for different frequency points on the mirror,achieving coupling of correction amounts at two frequency points on the same mirror.A spatial power combiner designed based on this method achieves over 95%efficient power combination within a relative bandwidth of 43%,significantly enhancing the bandwidth performance of the mirror system compared to power combiner designed using traditional methods with a relative bandwidth of only 12.5%.