| Enhancing the output frequency and radiation power of the high power microwave system is the inevitable trend of HPM technology in line with its further development and application. At present, a gigawatt-level output power of microwave sources has been achieved at the relative low frequency bands, such as P-band, L-band, C-band and X-band. However, at the higher frequency band, like Ku-band which is widely used in the broadcasting and communications, the microwave sources mostly can only obtain hundred megawatt-level output power. Combining the output power of several HPM sources spatially in Ku-band turns out to be a technique with great potential. In order to combine the output power of multiple HPM sources in an antenna array efficiently, the sources must be phase-locked at the same frequency. Injecting an outer signal into one or several HPM oscillator(s) is an alternative way to achieve phase-locking. The coaxial TTO is an ideal microwave source for power combining because of its low impedance, high power capacity and low guided magnetic field. And it is conducive to long pulse operation and remission of the problems of devices at high frequency, such as space-charge limiting and RF breakdown.Based on the above, a Ku-band coaxial TTO with an injected signal to lock its phase is presented in this thesis, to provide technical support for power combining. The main contents are as follows.Firstly, the condition for phase-locking of oscillators is derived based on classical theory. According to the circuit matching theory, the injecting matching conditions for input cavity are achieved. And based on that, an input cavity with an absorbing ratio of 90% is designed. On the basis of the small signal theory in resonant cavity, the tri-modulated cavity is designed, the electron beam conductance of three modes inside is calculated and the ?/2 mode is selected as the operating mode.Secondly, the presented TTO is studied by PIC particle simulations, which indicates that: with an electron beam of 383 k V voltage and 9.6 k A current, an injected signal of 14.164 GHz frequency and an injection ratio of 0.03, a microwave of 1 GW and 14.164 GHz is obtained. The beam-wave exchange efficiency is 27.7% and the bandwidth of phase-locking is 5 MHz. The RF field distribution, the electron beam modulation, the transit-time effect, and the influence factors among structure parameters are also analyzed. And the simulation results also demonstrate the importance of the reflector in device.Finally, the phase-locking characteristic of the Ku-band TTO is studied by PIC simulation. The influence of the injection ratio, frequency mismatch, time of injection and voltage stability on the phase-locked characteristic is analyzed. Simulation results demonstrate that, a high-power injecting signal can lock the frequency and phase of the output microwave of the proposed device and improve the output capacity. When the frequency mismatch between the injected signal and the free-running coaxial TTO is 72 MHz(±36 MHz), an injection ratio of 0.11 can lock the phase, which also suggests that the injection power needed to achieve phase-locking is much lower than that predicted by Adler's theory. Moreover, the injected signal plays a role of inducing the electron beam during the early time of starting oscillation and suppressing the mode competition effectively. The variety of diode voltage, thickness of the electron beam, guiding magnetic field and drifting length have an effect on the phase-locking, especially the diode voltage. |
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