Research On The Effect Of Inner Surface Roughness Of Waveguides On Performances Of Electromagnetic Waves

With the successful development of radars, microwave technology is growing fast as a specialty discipline. At microwave frequencies, the guided-wave system is needed to transmit electromagnetic wave, which can meet the essential requirements of microwave transmission, such as low losses, high efficiency, bulky power, and so on. As a useful and common component, waveguide is getting more and more attention. However, the performances of waveguides can not satisfy the needs due to some fabrication factors in practice. The inner surface roughness is a critical one. Roughness will increase the losses and waste the energy. Considering the effect of roughness, an experimental formulation is applied, which is based on test results. However, the theoretical deduction is scanty. In addition, the experimental formulation is not fit for partial roughness. This thesis makes a research on this problem. Starting from Maxwell equation and the skin effect of microwave transmission, the increased conduction attenuation of waveguide is calculated according to the rough surface boundary, which is analytic.Firstly, the thesis presents the basic principle of microwave and waveguide transmission, characteristic parameters of rectangular waveguide, and calculation of conduction attenuation. It explains that roughness can increase the conduction attenuation and losses and waste energy. Then definition and characterization of surface roughness are brought out. Some modeling methods of surface roughness in the calculation of electromagnetic fields are summarized, whose disadvantages are pointed out. According to the Fractal Geometry Theroy, a better model of surface roughness is built. Based on this model, the effect of surface roughness on conduction losses is analyzed, whose result is analysis formula. The analysis takes partical roughness into account. In the end, the analytic expression of the effect of roughness on the conduction losses and attenuation of waveguide is brought out and proved by compared with results of reference. Take waveguides at K and Ka frequencies for example, the conduction losses and attenuation is calculated. It shows that the experimental formulation is not fit for partical roughenss, and that surface roughness will incrase the conduction losses by one time.