| The gyro-TWT is a high power source with simple structure, high power, high gain, high efficiency and broad bandwidth capabilities in millimeter wave band. But the instability problem is due to self-oscillation, it restricts gyro-TWTs'capability. Hence, how to restrain the self-oscillation are the main directions of gyro-TWTs at present.In this thesis, the stability of the distributed dielectric loaded gyro-TWT amplifier has been analyzed through theoretical analysis, numerical calculation and simulation.The main results are as follows:1. The self-oscillation of the gyro-TWT is investigated in detail. Using the small-signal dispersion equation and linear gain for a backward wave to analyze the absolute instability and backward-wave oscillation of the spurious modes. When the attenuation exceeds 3dB/cm, the absolute instability of the operating TE0 1 mode is suppressed. When the attenuations exceed 2.5dB/cm, 4.5dB/cm and 4.2dB/cm respectively, the backward-wave oscillations of the spurious modes are suppressed.2. Using the field matching and small-signal theory, the high frequency structure with dielectric distribution loaded is investigated. When thickness of the dielectric is 1.4mm, relative permittivity is 11-2.2j, the attenuation of the operating TE0 1 mode is 3.42dB/cm, the attenuations of spurious modes HE1 1, HE 21 and TE0 2 attain 3.07dB/cm, 10.53dB/cm and 16.42dB/cm respectively. They all satisfy the requests of suppressing the self-oscillation.3. According to modifying the small-signal dispersion equation, the expression about small-signal gain of the dielectric loaded gyro-TWT is gained. The methods about ensuring relatively high gain are achieved. They also can suppress the self-oscillation.4. Using the HFSS to simulate the high frequency structure of the dielectric distribution loaded gyro-TWT. The results indicate this structure can suppress the self-oscillation and ensure the high efficiency. |
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