Study On The Coupling Of Microwave Pulses Into The Cavity With Aperture Arrays And The Cavity With A Dielectric Slot

The study on the coupling of the microwave into slots on cavities is a key problem for the application of high-power microwaves (HPM's), the anti-HPM system-hardening systems, and the electromagnetic compatibility. The particle simulation software based on finite-difference time-domain algorithm is employed to investigate the coupling process of the microwave pulse into the rectangular cavity with aperture arrays and rectangular cavity with a dielectric slot in this thesis.First, the coupling process of the microwave pulse into the rectangular cavity with a dielectric slot is simulated. The phenomena of field enhancement, cavity modulation, spectrum separation effect, and pulse width stretch are investigated. The parameters of the microwave pulse, including the carrier frequency, pulse width, and the direction of polarization of the electric field of the microwave, which could affect the coupling process are also investigated. The coupling function method is employed to analyze the coupling resonant peak, resonant frequency, and the internal distribution of the electric fields coupled into the cavity. The influence of the direction of polarization of the incident electric fields on the coupling function is discussed. The resonant effect of the system is analyzed in detail, and the influence of the cavity effect on the coupling process is investigated. The factors that influence the coupling resonant peak and resonant frequency of the dielectric slot, including the slot length and slot width, are also discussed.The dielectric filled in the slot on the cavity has an important effect on the coupling process of microwave pulse into the cavity. Some new phenomena could possibly appear. The dielectric filled in the slot has an obvious attenuation effect on the electric field of the microwave pulse which couples into the cavity. The phenomenon of field enhancement and the electric field coupling into the cavity are weaker than that in the case in which there is no dielectric in the slot. The slot filled with a dielectric can be approximately considered as a small dielectric rectangular waveguide, and the group velocities of electromagnetic waves with different carrier frequencies propagating in the dielectric slot are quite diverse, which makes the phenomena of pulse width stretch more obviously. The times at which the maximum and minimum values of electric fields of the coupling microwaves appear in the dielectric slot are quite different after the incident waves of different carrier frequencies couple into the dielectric slot With the carrier frequency of the incident wave increasing, the group velocity of the microwave in the dielectric slot also increases and the maximum value of the electric field of the coupling wave appears early. The dielectric constant of the dielectric that is filled in the slot has an obvious effect on the coupling resonant peak and resonant frequency. With the increase of the dielectric constant of the dielectric that is filled in the slot, the coupling resonant frequency at the center of the dielectric slot decreases and the resonant peak keeps almost the same. The formulation of the resonant frequency for the microwave coupling into a slot, which was obtained before, is not applicable to the case of a dielectric slot, and the new formulation of resonant frequency for the microwave coupling into a dielectric slot is derived using a lot of numerical results through fitting investigation, and is validated with the numerical simulations. We find that the formulation fits well with the simulation data.Secondly, the coupling process and the coupling characteristics of the microwave pulse into the rectangular cavity with aperture arrays are investigated. The phenomena of field enhancement, cavity modulation, spectrum separation effect, and pulse width stretch are also observed in the computer simulations. The conclusions which have been obtained before, such as the factors that influence the coupling electric fields and the peak power of the microwave pulse coupling into the cavity with aperture arrays, including the area, shape, number, and the spacing between slots in aperture arrays, are validated.However, we obtain some new conclusions. The phenomena of field enhancement at each center of the slot in the aperture arrays in the process of microwave pulse coupling into the rectangular cavity with aperture arrays is observed in the computer simulation. We find that, in the case in which the aperture array distributes parallel to the direction of the electric field of the incident microwave pulse, the effect of field enhancement of the slot in the middle of aperture array is the weakest, and the effect of field enhancement increases symmetrically in turn for the slots from the middle of the array to both ends of the array; while in the case in which the aperture array distributes perpendicular to the direction of the electric field of the incident microwave pulse, the effect of field enhancement of the slot in the middle of aperture array is the strongest, and the effect of field enhancement decreases symmetrically in turn for the slots from the middle of the array to both ends of the array. We also investigate the factors that influence the effect of field enhancement at the center of each slot and the coupling electric field distribution in the cavity, including the number of slots and the spacing between slots. With the number of slots increasing, the effect of field enhancement at the center of each slot is decreased, but the coupling electric fields in the cavity and the peak power of the microwave pulse coupled into the cavity is increased. With the spacing between the slots increasing, the effect of field enhancement at the center of each slot, the coupling electric fields in the cavity, and the peak power of the microwave pulse coupled into the cavity are all increased.