耦合腔慢波電路的三維軟件冷測模擬

討論了在考慮行波管管殼影響的情況下,使用MAFIA模擬軟件軟件的冷測方法模擬耦合腔慢波電路的高頻特性參數，包括色散特性、耦合阻抗和衰減特性，使色散特性精度提高到0.29%，其模擬結果比忽略管殼影響下的計算值更加接近實驗數據，也證明了計算機模擬冷測方法可以取代實驗測試方法。
關 鍵 詞 軟件冷測; MAFIA模擬; 管殼影響; 高頻特性參數

In the course of traditional design，the method that coupled-cavity slow-wave characteristic data gained by cold-test experiment is called hardware cold-test，while by software simulation is called software cold-test. Software cold-test method may reduce the time and cost of Traveling-Wave Tube research and manufacture，and design some novel slow-wave structure to avoid costly hardware cold-test and shorten development periods.
The slow-wave characteristic data includes high-frequency dispersion characteristic、interaction impedance and attenuation characteristic. In the hardware cold-test experiment，dispersion curve is gained by resonance method testing resonance frequency point per cavity phase shift. Interaction impedance is calculated using a special calculation equation expression by perturbation method testing resonancefrequency shift.
So far many papers discuss the method by software simulation obtaining such characteristic data. Three-dimension electromagnetism software-MAFIA 4.1 releases is the tool software of simulation cold-test data. After thinking over existed simulation method by MAFIA software，we find that existed simulation often ignored effect of tube-envelop，and directly set electric wall boundary condition in the structure boundary. The simplification method cannot accord with the fact condition. Now the paper improve simulation method by considering effect of tube-envelop，then making the result more consistent with hardware cold-test experiment data than the method that ignoring effect of tube-envelop.

1 Coupled Cavity Structure model
The paper models the 961HA couple cavity TWT slow-wave circuit which parameter is gained in the paper[1]. The 961 HA couple cavity TWT is used in the intersatellite communications which performance is 70 w and 59~64 GHz，a very important device in millimeter waveband TWT. The main view and cross section view of the slow-wave circuit is displayed figure 1.

2 Simulation and Result
2.1 Electric field Distribution
The both ends of the circuit is separately set different boundary condition by E module in MAFIA after automesh. After the circuit is solved by the E-solver，we may obtained eigen-frequency and electromagnetic field distribution corresponding to different boundary condition. The full of course simulating three kind of different boundary condition spend 3 hour and 12 minute using digital 400i workstation.
Electric field distribution for cavity mode in couple cavity simulating by MAFIA software is the same as that of kantrowitx.F’s paper[2]. The relationship of phase shift per cavity with eigen-frequency is gained by different electric field distribution，then data of couple cavity dispersion characteristic is gained by the frequency-phase relationship. The contrast figure of electric field distribution for cavity mode in kantrowitx.F’s paper with MAFIA simulation result is displayed in figure 2.