# Shielding Grounding Optimization Method for Spaceborne Multi-Cable
## 2 Shielding Grounding Optimization Method
### CST Modeling and Simulation  
As shown in Figure 2, the number of cables was set as \(i\), denoting them as \(C_{1},C_{2},\ \dots,\ C_{l}\). The cable lengths are \(L_{1},L_{2},\ \dots,\ L_{i}\). The vertical heights of the cable from the reference plane are \(H_{1},H_{2},\ \dots,\ H_{i}\), respectively. \(D_{12}\) represents the horizontal distance between \(C_{1}\) and \(C_{2}\), etc. Each cable was wrapped in shielding. The two ends of the shield were grounded through the resistance. The side near the signal-sending end is called the near end, and the subscript is \(N\). The grounding resistance of the near end is \(R_{1N},R_{2N},\ \dots,\ R_{iN}\). The side near the receiving end of the signal is called the far end, and the subscript is \(F\). The grounding resistance of the far end is \(R_{1F},R_{2F},\ \dots,\ R_{iF}\). Actual cables may be bent and stacked, which greatly increases the difficulty of modeling. In addition, the positions and states of cables may not be identical each time during actual tests. Therefore, modeling a cable in strict accordance with a cable shape is not universal and is not important. In addition, the bending and stacking of cables may affect the signals inside the cables, which may impact subsequent test results and lead to a misjudgment of the shielding effect. Therefore, this study only considered the simplest parallel cables and eliminated the influence of the bending and stacking of cables to analyze the shielding effect of the shield under different grounding states. Figure 1: Shielding grounding optimization process. Figure 2: Grounding structure of multiple cable shields. In the actual electronics system, the grounding status of the cable shield varies, including double-terminal grounding, ungrounded, single-terminal grounding at the near end, and single-terminal grounding at the far end. Therefore, it was necessary to parameterize each physical quantity shown in Figure 2, so that all the ground states could be traversed using parameter scanning. However, there are two special cases in the parameterization process, one of which is that, when the shield of an actual cable is not grounded, according to the traditional modeling method, the grounding resistance needs to be removed and the simulation needs to be run again, which undoubtedly increases the manual operation cost and time complexity in the case of multiple cables and multiple states. Therefore, this paper proposes the processing method of parameter extremization, i.e., increasing \(R_{iN}\) and \(R_{iF}\) to certain values to simulate the cable state as ungrounded, which avoids frequent modifications to the model and greatly facilitates the automatic parameter scanning process of CST. The other issue is that, if the CST requirements for some of the model's physical size parameters mean that they must be set greater than 0, the model will not be able to set the shield thickness to 0 mm to simulate an actual cable without a shield. It is also necessary to address the extremes of the shield thickness parameter, i.e., when the thickness is reduced to a certain value to simulate an actual cable without a shield. However, such parameter extremization processing does not represent a real state, and would therefore cause errors. Therefore, it was necessary to further judge the degree of parameter extremization to ensure that the error between the result and the real state was within an acceptable range. The following is an example of resistance parameter extremization. In the CST example model shown in Figure 3, the simplest case was considered, where the interfering line \(C_{1}\) is a single cable, and the interfered line \(C_{2}\) is a coaxial cable, \(D_{12}=5\) cm: \(H_{1}=H_{2}=5\) cm. A sinusoidal voltage excitation of different frequencies with an amplitude of 30 V was applied in \(C_{1}\), \(R_{2N}\) was increased, and the peak magnitude of the disturbance voltage in \(C_{2}\) was simulated. Finally, the grounding resistance of \(C_{2}\) was removed, and the simulation result was used as a benchmark for comparison.