Applied Research Of Transmission Line Theory In Electromagnetic Shielding Of Fog North Seeker

In order to resist electromagnetic interference, electromagnetic shielding becomes more and more popular in every field. Though there are many numerical methods which can obtain accurate simulation data, they cost too much long time and tremendous computing workload. It is an enormous waste of resources. So, the analytical method becomes the more effective method in the modeling of the electromagnetic shielding.The FOG North Seeker is taken as an object, and the application of transmission line theory is used in the modeling of typical shielding cavities in the real project, which include single-layer, double-layer, three-layer rectangular cavity with apertures, cavity with apertures in different sides, and cavity with PCB inside. The shielding effectiveness of any point in these cavities are researched respectively, which supplies good reference value for the cavity and aperture designing and devices layout in the real project. The main works and innovations are listed as follows:1. For the actual situation of the electromagnetic wave incidents into the cavity at an arbitrary angle, the method of introducing vertical incident angle, horizontal incident angle, and polarization angle is proposed. The coordinate of the plane electromagnetic wave is converted from the incident source coordinate system to the rectangular cavity coordinate system, and the model is analyzed based on the horizontally polarized component and the vertically polarized component especially. The electromagnetic wave can incident into the cavity at an arbitrary angle with this modeling method, which increases the fitness of the model and the practical situation.2. For the actual situation of the aperture locates at any position of the cavity face, the method of the aperture is taken as the asymmetrical coplanar stripline is proposed. The aperture is modelled according to the transmission line model with distributed voltage sources, and the equivalent voltage produced at the center of the aperture is taken as the voltage source of the whole circuit model. This modeling method saves calculation time. The location of the aperture is extended to any location on the cavity's face from the center, which increases the applicability of the model.3. For the actual situation of the probe point locates at any position in the cavity, the method of describing the electromagnetic distribution with mode voltage and mode current is proposed. The rectangular cavity is taken as a rectangular waveguide with one end completely open and another end completely closed. The waveguide is combined with aperture, and the total power supply transmission line model is used in the analysis. Considering the higher-order modes of TE mode and TM mode, and combining the distribution of electric field in the cavity, the shielding effectiveness of any point in the cavity is solved. This modeling method extends the location of the probe point to any point in the cavity from the points on the center line of the aperture, which increases the engineering value of the model.4. Aiming at the FOG North Seeker, and according to the above methods, the shielding effectiveness of monolayer cavity, double layer cavity and three layers with apertures are modelled. The relationship between the shielding effectiveness and the location of the probe point and the relationship between the number of the layers and the shielding effectiveness are analyzed. The simulation results show that:the shielding effectiveness solved through the models agrees with the experimental data, which proves the accuracy of the models. The shielding effectiveness is different with the different probe point, and the shielding effectiveness is improved with the increase of the layers. That provides a good reference value for the devices or systems with high shielding effectiveness requirements in engineering practice.5. Aiming at the FOG North Seeker, the rectangular cavity with apertures in different directions and the rectangular cavity with printed circuit board (PCB) inside are modelled to solve the shielding effectiveness of the cavity. The simulation results show that:the shielding effectiveness is different with the different probe point, which gives good advice to the engineering practice.