High power traveling wave tubes and other microwave tubes are the core devices of radar and other electronic equipment, and their technical level determines the tactical performance of electronic equipment. However, due to the large gain fluctuation of high-power microwave tubes, under the condition of equal excitation input, all points in the frequency band cannot be saturated, which will cause harmonics and intermodulation components of the input signal, resulting in microwave vacuum tube defective products The rising rate, more importantly, directly affects the performance of modern electronic equipment, especially difficult to meet the high environmental reliability requirements of modern warfare. Therefore, it is necessary to use high-power microwave tube equalization technology, that is, adding a microwave network to make its transmission characteristics compensate for the transmission characteristics of the microwave tube, so that the output power fluctuation of the traveling wave tube is minimized. This microwave network is a microwave equalizer. Each microwave tube has different performance. The matching equalizer needs to be designed and debugged tube by tube. The design cycle is long and the cost is high. Computer-aided design can solve this problem well. Commonly used microwave simulation software based on moment method such as ADS, IE3D, FEKO, simulation software based on time domain finite difference method such as CST, IMSTEmpire, CFDRC, simulation software based on finite element such as AnsoftHFSS, AnsysEmax and so on. These simulation software can greatly reduce the product development cycle and development costs, but because the design frequency of microwave devices is getting higher and higher, the errors caused by ignoring the higher-order propagation mode in the simulation design, the environmental characteristics of materials in the design and The problem of the accuracy of the models built at microwave frequencies is a greater challenge to the simulation software. The research group has been studying the high-power microwave amplitude equalizer for many years. The modern radar fund project: the project supported by the National Natural Science Foundation of China (No.60071031) ) Designed several sub-structures of resonant cavity, summarized the role of various adjustment factors in the sub-structure, such as the length of the resonant cavity, probe insertion depth, fine-tuning screws and other factors, combined with the factors of material and temperature, accumulated a large amount Design data. According to the characteristics of the sub-structure interconnection of the microwave amplitude equalizer and the measurement data of the adjustment factors of the sub-structure, this paper presents the idea and method of the optimal design of the interconnected sub-structure network based on the measurement database of the sub-structure of the microwave amplitude equalizer. This method not only makes use of the precise structure of actual measurement, but also makes full use of the characteristics of the computer's large storage capacity and fast calculation ability, avoids the blindness of design and debugging, and has practical application value.
The structure and adjustment factor structure of the microwave amplitude equalizer is formed by interconnecting several sub-structures of the coaxial resonance cavity with the same structure. Each coaxial resonant cavity substructure is connected to the main transmission line at one end and a short-circuited piston at the other end. The length of the resonant cavity can be adjusted. In the resonant cavity, an adjustable probe is inserted into the main transmission line. Attenuating screws or metal fine-tuning screws made of absorbing material are used to couple the energy of the main transmission line into the resonant cavity through the coupling probe. The length of the resonant cavity and the depth of insertion of the probe are adjusted to adjust the resonant frequency of the resonant cavity An odd multiple of K / 4. The resonant length of the equalizer designed in this paper is 3K / 4. Adjusting the insertion depth of the attenuation screw can absorb part of the energy and form a loss, while changing the Q value of the resonator. In addition, fine adjustment screws or attenuation screws will also cause a slight shift in resonance frequency. Therefore, the resonance frequency, power attenuation, standing wave ratio and other properties of the microwave amplitude equalizer are determined by the combined effects of the adjustment factors such as cavity length, probe and fine adjustment screw, and attenuation screw. Due to the limited bandwidth of the single substructure and the absorption attenuation amplitude In order to achieve high-precision equalization of high-power traveling wave tubes in a wider frequency band, a multi-level sub-structure interconnection form is adopted, and the number of sub-structures is determined according to specific design requirements.
Analysis of sub-structure interconnection network The analysis method of sub-structure interconnection network is to solve the problem that some complex microwave structures are difficult to be analyzed by analytical methods and general numerical calculation methods. It is based on the existing microwave engineering experience and uses modern measurement technology to obtain microwave substructures Accurate data, and then a method of analyzing and optimizing complex networks based on sub-structure network cascading combined with computer technology. It mainly includes four aspects: substructure design method, substructure database establishment method, substructure interconnection network analysis theory and substructure interconnection network optimization design method. The basic idea is to treat the complex network as the interconnection of several substructures; you can directly use the substructure measurement data to construct a database that characterizes the characteristics of the network unit; obtain the total parameters of the network according to the microwave network theory; use data search, data interpolation, and database self-complete The technology directly uses the measurement database to effectively analyze and correct network parameters. The analysis method of interconnected network substructure can solve the problems of analysis and optimization design of networks with complex substructures.
For the equalization target curve required by the microwave tube, according to the characteristic parameters of the existing substructure, by selecting the appropriate number of substructures and adjusting the adjustable factors of the resonator to obtain the corresponding center frequency, quality factor and coupling coefficient, it can be Combining various curves can achieve a specific attenuation at a specific frequency point within a large bandwidth.
Establishment and modification of measurement database The massive database of microwave amplitude equalizer sub-structure is based on the existing engineering experience, adjusts many adjustment factors of sub-structure, and considers the influence of various environmental factors of the material. It is established through theoretical and experimental verification of network correction of.
For the convenience of measurement, both ends of the substructure contain fixed-length transmission line segments. In order to obtain accurate parameters of the substructure, the influence of the scattering parameters of the fixed-length transmission line segment must also be removed. Using T parameters and network cascade characteristics to get the modern radar 29 A parameter matrix representation (L) can also be used in the cascade of microwave networks. In fact, the program can be used to facilitate the conversion of A parameters, T parameters and S parameters.
Computer-aided design based on measurement database, part of the massive database based on measurement data, is the database obtained after the original measurement data is verified and corrected. The other part is the optimized objective function obtained according to the equilibrium curve required by the design. In order to reduce the amount of calculation, the sampling point is to determine its selection density according to the importance of the corresponding data to the fitting curve. Selection, so that the selected discrete value can reflect the oscillating nature of the function. The third part is to select a suitable optimization program for optimization. The data interpolation algorithm uses the distance reciprocal weight interpolation method. The optimization algorithm uses the sequence weighting factor method to balance the curve and the actual measured balance curve design curve (shown in solid line) and according to the design. The result is a slightly adjusted curve (shown by the dotted line). It is seen that the power attenuation curve has three resonance points, and the amount of power attenuation is different at different resonance points, where the power attenuation at F0 is larger, which is caused by two or more resonance cavities. achieve.
The optimization curve is close to the measured curve, and the maximum difference is less than 1dB. It can be seen that the method of computer-aided optimization design based on the measurement database is effective in actual engineering.
The microwave equalizer is formed by interconnecting several coaxial resonant cavity sub-structures of the same structure. Its design and debugging can use the computer-aided design of the interconnected sub-structure network based on the measurement database, and fine-tuning and correction in subsequent debugging. This network analysis and optimization method combines computer technology and microwave high-precision automatic measurement technology. It mainly includes four aspects: substructure design method, substructure database establishment method, substructure interconnection network analysis theory and substructure interconnection network optimization design method. This method of computer-aided design based on measurement database has practical engineering value, avoids the blindness of design and debugging, and can be extended to the design of other similar sub-structure interconnected microwave devices.
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