Study On The Coupling Of Microwave Pulses Into The Nonmetal And Metal Cavities With Slots

Research on the coupling of the microwave into slots on cavities is a key issue for the application of high-power microwaves (HPM), the anti-HPM system-hardening systems, and the electromagnetic compatibility. The particle simulation code based on finite-difference time-domain algorithm is employed to investigate the coupling process of the microwave pulses into the nonmetal cavity with a slot and the metal cavity with a slot in this thesis.There are two coupling ways of the microwaves into the nonmetal cavity with a slot. One is the microwave passing through the slot, the other one is the microwave passing through the nonmetal wall. The coupling process of the microwave pulses into the nonmetal cavity with a slot is simulated by a PIC code. The results show that some conclusions of the coupling process of the microwave pulse into the nonmetal cavity with a slot are similar to those of the coupling process of the microwave pulse into the metal cavity with a slot. The phenomena of pulse width stretch, time delay of the group waves, and polarization characteristics are found in the coupling process of the microwave pulse into the nonmetal cavity with a slot. Such phenomena could be intensified by increasing the dielectric constant. With the increase of the thickness of the cavity, the coupling electric field and the coupling power in the cavity decrease. The coupling power passing through the slot increases when area of slot increases or aspect ratio of the slot increases.We also find some new phenomena. We give the distribution of the coupling electric field in the cavity, and the results show that the coupling electric field in the slot of the nonmetal cavity is clearly attenuated while the coupling electric field in the slot of the metal cavity is strengthened. For a low dielectric constant, the spectrum separation effect and the resonance effect are not found in the nonmetal cavity case and the coupling electric field is attenuated rapidly, while the spectrum separation effect and the resonance effect are obivious in the metal cavity case and the coupling electric field is attenuated very slowly. For a high dielectric constant, at the center of the cavity the spectrum separation effect is obvious, and at the center of the slot the multi-peak resonance is found. The resonance frequency of the nonmental cavity decreases as the dielectric constant increases, while the resonance frequency of the metal cavity is only related to the dimension of the slot. The coupling electric field at the high frequency range attenuates more intensely than that at the low frequency range in the nonmetal cavity case, and the attenuation frequency range is extended when the dielectric constant increases. In the metal cavity case, only the microwave whose frequency is closed to the resonant frequency can easily couple into the metal cavity with a slot. When the dielectric constant increases, the coupling electric field at the center of the cavity increases first and then decreases, and the coupling electric field at the center of the slot decreases. The coupling electric field and the coupling power in the cavity decrease slowly with the increase of the cavity wall conductance. With the dielectric constant less than 15, the slot area less than 4.0cm2 , and the thickness of the cavity less than 10cm, the coupling power of the microwave of 5GHz passing through the slot of the nonmetal vavity is much less than the total coupling power in the cavity. With the increase of the dielectric constant and the slot area and the thickness of the cavity, the ratio of the coupling power passing through the slot to the total coupling power goes up.One of the most important contributions in this thesis is that the coupling process of the microwave pulse into the metal cavity with a slot is numerically simulated, which shows a new conclusion that the coupling process of the microwave pulse into the metal cavity with a narrow rectangular slot exists the multi-peak resonances. Using simulation results and theoretical analysis, we obtain an important formula describing the multi-peak resonances, which is f_n= (2n + 1) c/2a , n= 0,1,2.....